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Freshwater jellyfish (= limnic medusa‐budding hydrozoans, FWJ) are a small group of cnidarians found on all continents except Antarctica in temperate to tropical latitudes. Members of this group belong primarily to three genera: Astrohydra, Craspedacusta, and Limnocnida. While Astrohydra and Limnocnida are typically restricted to the islands of Japan, Africa, and the Indian subcontinent, one species or potential species complex, Craspedacusta sowerbii, became globally invasive. Despite research going back about one‐and‐a‐half centuries, little is known about their phylogeny and ecology compared to marine jellyfish. Recent species distribution modelling, however, showed that by 2050, C. sowerbii will potentially extend their distribution ranges due to global warming to high‐latitude ecosystems and be present (medusa stage) for an extended time in the seasonal limnic production cycle. An increase in their relative ecological importance with temporal and spatial spreading is hypothesised. Only recently, it has been shown that the trophic roles of polyps and medusae and their prey overlap with other ecosystem members. In addition, medusa behaviour may cause trophic cascades and alter vertical nutrient distributions. However, polyps and other benthic life cycle stages are understudied. In globally, changing freshwater ecosystems that may become more accommodating for FWJ, an improved understanding of their population biology and ecosystem ecology is urgently needed. In this integrative review, we, therefore, explore reasons for the hampered historical research progress, contrast developments with those of marine cnidarians, compile and publish alongside an extensive and unprecedented literature database, and formulate avenues for future directions in FWJ research. [ABSTRACT FROM AUTHOR]

In this study, we described and compared the diet, monthly feeding intensity, and condition of west coast steenbras (Lithognathus aureti) and silver kob (Argyrosomus inodorus) caught at a unique habitat in the northern Benguela. Stomach contents of 179 west coast steenbras and 114 silver kob caught from October 2020 to September 2022 were investigated. The peak in feeding intensity of west coast steenbras appeared to be opportunistic during winter and summer periods depending on food availability. The fish condition, however, peaked at the beginning (October) and at the end (April) of the austral summer spawning period, with the hepatosomatic index (HSI) at 1.5% and the condition factor (CF) at 0.022%. Seven prey taxa were found in the diet of west coast steenbras (bivalves, bony fishes, other mollusks, algae, crustaceans, cnidaria, and polychaetas) and six taxa in the diet of silver kob (bivalves, crustaceans, bony fishes, algae, starfish, and zooplankton), indicating generalist feeding behavior in both the species. The bivalves were the most important prey items in the diet of west coast steenbras (95.9% index of relative importance [IRI]). The most important prey items in the diet of silver kob were crustaceans (83.1% IRI) and bony fishes (16.0% IRI). Crustaceans were most important in the diet of small‐to‐medium‐sized silver kob, whereas bony fishes were most important in the diet of larger silver kob (>75 cm), with significant differences of IRI% by size class. Schoener's index of niche overlap indicated a relatively low overall niche overlap (0.11) between west coast steenbras and silver kob. This allows them to coexist as their feeding habits allow them to occupy unique niches in the coastal reef and sandy habitat and reduce competition for resources. [ABSTRACT FROM AUTHOR]

Calcareous skeletal structures are common among different invertebrate groups, including Porifera, Cnidaria, Platyhelminthes, Mollusca, and Echinodermata. They appear externally as shells, plates, or scales, or internally as subepidermal spicules. Although typically formed outside of the cells, in one class of gastropod molluscs, the Heterobranchia, subepidermal and intracellular spicules are found—a rare case, at least for the molluscs. This type of spicules is present in several phylogenetically distant groups of heterobranch molluscs (Rhodopemorpha, Acochlidimorpha, and Nudibranchia), each different in terms of morphology and autecology. This raises questions about the origin and homology of subepidermal spicules in heterobranch molluscs. To answer these questions, understanding the process of spicule formation is crucial. This is impeded by insufficient data on the fine structure of the subepidermal spicules and adjacent epithelia. To address this problem, we carried out a comprehensive morphological study of subepidermal spicules and the body wall in one species of Acochlidimorpha. We revealed variations in the cellular composition of the epidermis, musculature organization, and spicules' arrangement, which most likely reflect the different functional roles of the spicule complex within Heterobranchia representatives. However, the obtained data are insufficient to answer the question of the origin of spicules and their homology within Heterobranchia. [ABSTRACT FROM AUTHOR]

Cnidarians—the phylum including sea anemones, corals, jellyfish, and hydroids—are one of the oldest groups of predatory animals. Nearly all cnidarians are carnivores that use stinging cells called cnidocytes to ensnare and/or envenom their prey. However, there is considerable diversity in cnidocyte form and function. Tracing the evolutionary history of cnidocytes may therefore provide a proxy for early animal feeding strategies. In this study, we generated a time‐calibrated molecular clock of cnidarians and performed ancestral state reconstruction on 12 cnidocyte types to test the hypothesis that the original cnidocyte was involved in prey capture. We conclude that the first cnidarians had only the simplest and least specialized cnidocyte type (the isorhiza) which was just as likely to be used for adhesion and/or defense as the capture of prey. A rapid diversification of specialized cnidocytes occurred through the Ediacaran (~654–574 million years ago), with major subgroups developing unique sets of cnidocytes to match their distinct feeding styles. These results are robust to changes in the molecular clock model, and are consistent with growing evidence for an Ediacaran diversification of animals. Our work also provides insight into the evolution of this complex cell type, suggesting that convergence of forms is rare, with the mastigophore being an interesting counterexample. Highlights: Cnidarian stinging cells diversified through the Ediacaran, demonstrating that animal predation evolved before the Cambrian explosion. The mastigophore is rare case of a complex cell type evolving more than once. [ABSTRACT FROM AUTHOR]

The deep‐sea corals Dendrophyllia ramea and Dendrophyllia cornigera occur in Mediterranean and Atlantic waters. Both species are found in different environmental conditions, and they can colonize hard and soft substrates. These species then display an important ecological plasticity along with morphological plasticity. Nevertheless, there is a large knowledge gap on the genetic characteristics of the two species, including on the relationships between them and the possibility of cryptic species along their range. The recent discovery of Dendrophyllia populations off Cyprus in the eastern Mediterranean Sea raised new questions in this context. These corals were related to D. ramea but had some morphological differences with other known populations of this species. Here, we study the specific status of Dendrophyllia corals from Cyprus on the basis of morphology and genetics. The genetic data are interpreted by comparison with the same analysis performed on two Caryophyllia species. Both morphological and genetic data confirm that corals found off Cyprus belong to the D. ramea species. We further tested the speciation scenario using transcriptome data: the results indicate an absence of current gene flow between D. ramea and D. cornigera and that the divergence occurred more than 3 million years ago. We discuss the possible historical and ecological factors which may have shaped speciation in these species. [ABSTRACT FROM AUTHOR]

The cnidom and intraspecific variability of cnidae within the small sea anemone Isactinia sp. were verified. The specific cnidae within the cnidom of four discrete morphological structures (tentacle, actinopharynx, mesenterial filaments, and body column) within Isactinia sp. was investigated. Microbasic b‐mastigophores, microbasic p‐mastigophores, basitrichs, microbasic p‐amastigophores, and spirocysts were found in this species. In addition, two morphologically distinct basitrich forms, distinguishable only in a discharged state, were also found, of which basitrichs with the distinctly shorter thread were found predominately only on the body column. The distribution and abundance of cnidae types differed significantly around the body in the sea anemones, as did the length of basitrichs and spirocysts among tissue types. Cnidae length also differed significantly among individuals. Correlations between cnidae length and sea anemone size were variable, whereby cnidae size was significantly negatively correlated to sea anemone size in seven cnidae–tissue combinations, positively correlated in one, and not correlated in two. Linear regression revealed that sea anemone size was able to explain 33%–68% of variation in size of b‐mastigophores, p‐amastigophores, and small basitrichs from within the mesenterial filaments. Correlations were negligible or not significant in remaining cnidae–tissue combinations, however. While providing key taxonomic cnidae information, this study also highlights the variability of cnidae that may occur within a species of Isactinia. [ABSTRACT FROM AUTHOR]

Endometrial polyps are rare benign uterine masses exclusively reported in geriatric, entire, female dogs or spayed female dogs with ovarian remnant syndrome. A 12‐year‐old, female, ovariohysterectomised cocker spaniel was presented for hyporexia, progressive muco‐haemorrhagic vulval discharge, and an ultrasonographically detected caudal abdominal mass. Thoracic and abdominal computed tomography revealed that the mass originated from the uterine stump, with no evidence of metastasis. Surgical excision of the mass was performed, and histopathology of the mass was consistent with an endometrial polyp. The dog was confirmed to be neutered based on the absence of ovarian remnant found on computed tomography and during surgery, and the negative results of both anti‐Mullerian hormone test and human chorionic gonadotropin stimulated progesterone test. The dog fully recovered with complete resolution of clinical signs at 2‐week, 6‐month and 18‐month rechecks. The presenting case highlights the first reported case of an endometrial polyp in a spayed female dog. [ABSTRACT FROM AUTHOR]

Staurozoa is a small group of marine stalked jellyfish, some of which have specialized attachment organs — rhopalioids, or so‐called anchors. The adhesive function of these organs was mentioned in numerous studies; however, the mechanism of their temporary attachment is still unknown. Moreover, it is assumed that rhopalioids may be homologous to rhopalia of scypho‐ and cubozoans and provide sensory and integrative functions. Nevertheless, nervous elements associated with rhopalioids are poorly investigated. Thus, we focused on morphological features of rhopalioids in staurozoan Haliclystus auricula James‐Clark, 1863 using histological and semithin sections, and also confocal laser scanning microscopy. We described histological organization of rhopalioids and observed four types of epidermal gland cell, which presumably provide the attachment and reattachment to the substrate. Supposedly, the musculature of rhopalioids can also play a role in the attachment and reattachment. We have studied organization of the nervous system in rhopalioids, which includes FMRFamide‐, tubulin‐ and neurotensin‐positive nerve clusters and FMRFamide‐positive presumptive sensory cells. Based on our results, we assume that rhopalioids, besides the complex attachment, may act like sensory organs and play a role of integrative centres. [ABSTRACT FROM AUTHOR]

Morphological identification of cnidarian species can be difficult throughout all life stages due to the lack of distinct morphological characters. Moreover, in some cnidarian taxa genetic markers are not fully informative, and in these cases combinations of different markers or additional morphological verifications may be required. Proteomic fingerprinting based on MALDI‐TOF mass spectra was previously shown to provide reliable species identification in different metazoans including some cnidarian taxa. For the first time, we tested the method across four cnidarian classes (Staurozoa, Scyphozoa, Anthozoa, Hydrozoa) and included different scyphozoan life‐history stages (polyp, ephyra, medusa) in our dataset. Our results revealed reliable species identification based on MALDI‐TOF mass spectra across all taxa with species‐specific clusters for all 23 analysed species. In addition, proteomic fingerprinting was successful for distinguishing developmental stages, still by retaining a species specific signal. Furthermore, we identified the impact of different salinities in different regions (North Sea and Baltic Sea) on proteomic fingerprints to be negligible. In conclusion, the effects of environmental factors and developmental stages on proteomic fingerprints seem to be low in cnidarians. This would allow using reference libraries built up entirely of adult or cultured cnidarian specimens for the identification of their juvenile stages or specimens from different geographic regions in future biodiversity assessment studies. [ABSTRACT FROM AUTHOR]

Aim: Climate‐driven trends in environmental processes and their effect on marine ecosystems remain poorly understood despite an obvious decrease in marine biological resources which undergo changes in stock size mediated by phyto‐ and mesoplankton. A mesoplankton multiannual dataset is one of the best tools to elucidate general trends in marine ecosystems. Location: Oligo‐ and mesotrophic waters of the Central Atlantic. Time Period: 1950–2016. Major Taxa Studied: Chaetognatha, Cnidaria, Crustacea, Mollusca. Methods: Wet mesoplankton biomass (B) values were estimated in 1159 mesoplankton (animals 0.5–30.0 mm long) samples collected in the open ocean epipelagic (0–200 m) in 1950–2016. We ran Generalized Linear Mixed Models and analysed general trends in B, in satellite‐derived surface chlorophyll (Chl, as a proxy of phytoplankton biomass in 1998–2015), and surface temperature (SST, NCEP/NCAR reanalysis, 1948–2015). We further compared the multiannual trends in B, SST, Chl and in space of the oligotrophic and mesotrophic Chl contours in selected regions and in the whole Central Atlantic. Results: We showed a statistically significant decline of B within the whole Central Atlantic (9‐fold during 1950–2016) and within each of the three selected regions. These trends were always coupled with other statistically significant effects: increase of SST, decline of Chl, expansion of Chl‐depleted areas and shrinkage of Chl‐enriched areas. Main Conclusions: The results unveil the following causal relationship in the Central Atlantic: SST increase → strengthening of stratification → Chl decline—expansion of low‐productive areas → B decrease, which, along with existing prognostic climate models, suggests future mesoplankton decline in the Central Tropical Atlantic. The decline in Chl and B is expected to amplify decrease of higher trophic levels biomass and thus to result in changes in the marine food webs. Observed changes in biomass and production will imply direct repercussions for world fisheries and other services provided by Ocean. [ABSTRACT FROM AUTHOR]

N6‐methyldeoxyadenosine (6mA) is a chemical alteration of DNA, observed across all realms of life. Although the functions of 6mA are well understood in bacteria and protists, its roles in animal genomes have been controversial. We show that 6mA randomly accumulates in early embryos of the cnidarian Hydractinia symbiolongicarpus, with a peak at the 16‐cell stage followed by clearance to background levels two cell cycles later, at the 64‐cell stage—the embryonic stage at which zygotic genome activation occurs in this animal. Knocking down Alkbh1, a putative initiator of animal 6mA clearance, resulted in higher levels of 6mA at the 64‐cell stage and a delay in the initiation of zygotic transcription. Our data are consistent with 6mA originating from recycled nucleotides of degraded m6A‐marked maternal RNA postfertilization. Therefore, while 6mA does not function as an epigenetic mark in Hydractinia, its random incorporation into the early embryonic genome inhibits transcription. In turn, Alkbh1 functions as a genomic 6mA "cleaner," facilitating timely zygotic genome activation. Given the random nature of genomic 6mA accumulation and its ability to interfere with gene expression, defects in 6mA clearance may represent a hitherto unknown cause of various pathologies. Synopsis: The presence and functions of N6‐methylation of deoxyadenosine (6mA) in animal genomes are disputed. This study shows that N6‐methyladenosine (m6A)‐decorated maternal RNA is the source of 6mA in cnidarian embryonic genomes, from which it has to be removed for initiation of zygotic transcription.Rapid degradation of m6A‐marked maternal RNAs generates a nucleotide pool containing m6A.After NTP‐to‐dNTP conversion by a ribonucleotide reductase, 6mA is randomly incorporated into the embryonic genome.Genomic 6mA interferes with embryonic transcription.Removal of 6mA by the 6mA dioxygenase Alkbh1 facilitates timely zygotic genome activation. [ABSTRACT FROM AUTHOR]

Multisensory integration (MSI) combines information from more than one sensory modality to elicit behaviours distinct from unisensory behaviours. MSI is best understood in animals with complex brains and specialized centres for parsing different modes of sensory information, but dispersive larvae of sessile marine invertebrates utilize multimodal environmental sensory stimuli to base irreversible settlement decisions on, and most lack complex brains. Here, we examined the sensory determinants of settlement in actinula larvae of the hydrozoan Ectopleura crocea (Cnidaria), which possess a diffuse nerve net. A factorial settlement study revealed that photo‐, chemo‐ and mechanosensory cues each influenced the settlement response in a complex and hierarchical manner that was dependent on specific combinations of cues, an indication of MSI. Additionally, sensory gene expression over development peaked with developmental competence to settle, which in actinulae, requires cnidocyte discharge. Transcriptome analyses also highlighted several deep homological links between cnidarian and bilaterian mechano‐, chemo‐, and photosensory pathways. Fluorescent in situ hybridization studies of candidate transcripts suggested cellular partitioning of sensory function among the few cell types that comprise the actinula nervous system, where ubiquitous polymodal sensory neurons expressing putative chemo‐ and photosensitivity interface with mechanoreceptive cnidocytes. We propose a simple multisensory processing circuit, involving polymodal chemo/photosensory neurons and mechanoreceptive cnidocytes, that is sufficient to explain MSI in actinulae settlement. Our study demonstrates that MSI is not exclusive to complex brains, but likely predated and contextualized their evolution. [ABSTRACT FROM AUTHOR]

Cnidarians are the most primitive metazoans, but their evolutionary relationships are poorly understood, although recent studies present several phylogenetic hypotheses. Here, we collected 266 complete cnidarian mitochondrial genomes and re‐evaluated the phylogenetic relationships between the major lineages. We described the gene rearrangement patterns of Cnidaria. Anthozoans had significantly greater mitochondrial genome size and lower A + T content than medusozoans. Most of the protein‐coding genes in anthozoans such as COX 13, ATP6, and CYTB displayed a faster rate of evolution based on selection analysis. There were 19 distinct patterns of mitochondrial gene order, including 16 unique gene orders in anthozoans and 3 mtDNA gene orders pattern in medusozoans, were identified among cnidarians. The gene order arrangement suggested that a linearized mtDNA structure may be more conducive to Medusozoan mtDNA stability. Based on phylogenetic analyses, the monophyly of the Anthozoa was strongly supported compared to previous mitochondrial genome‐based analyses rather than octocorals forming a sister group relationship with medusozoans. In addition, Staurozoa were more closely related to Anthozoa than to Medusozoa. In conclusion, these results largely support the traditional phylogenetic view of the relationships of cnidarians and provide new insights into the evolutionary processes for studying the most ancient animal radiations. [ABSTRACT FROM AUTHOR]

Ion channels of the degenerin (DEG)/epithelial Na+ channel (ENaC) family serve diverse functions ranging from mechanosensation over Na+ reabsorption to H+ sensing and neurotransmission. However, several diverse DEG/ENaCs interact with neuropeptides; some are directly activated, whereas others are modulated by neuropeptides. Two questions arise: does this interaction have a common structural basis and does it have an ancient origin? Current evidence suggests that RFamide neuropeptides activate the FMRFamide‐activated Na+ channels (FaNaCs) of invertebrates via binding to a pocket at the external face of their large extracellular domain. It is likely that RFamides might activate DEG/ENaCs from the freshwater polyp Hydra (the HyNaCs) via binding to a similar pocket, although there is not yet any experimental evidence. In contrast, RFamide neuropeptides modulate acid‐sensing ion channels (ASICs) from vertebrates via binding to a central cavity enclosed by β‐sheets of the extracellular domain. Dynorphin opioid peptides, for their part, bind to the acidic pocket of ASICs, which might be evolutionarily related to the peptide binding pocket of FaNaCs, but instead of opening the channels they work as antagonists to stabilize its closed state. Moreover, peptides interacting with DEG/ENaCs from animals of different phyla, although having similar sequences, are evolutionarily unrelated to each other. Collectively, it appears that despite a seemingly similar interaction with similar peptides, the interaction of DEG/ENaCs with neuropeptides has diverse structural bases and many origins. [ABSTRACT FROM AUTHOR]

Temperature is a key abiotic factor controlling population dynamics. In facultatively sexual animals inhabiting the temperate zone, temperature can regulate the switch between asexual and sexual modes of reproduction, initiates growth or dormancy, and acts together with photoperiod to mediate seasonal physiological transitions. Increasing temperature due to recent global warming is likely to disrupt population dynamics of facultatively sexual animals because of the strong temperature dependence of multiple fitness components. However, the fitness consequences of warming in these animals are still poorly understood. This is unfortunate since facultatively sexual animals—through their ability for asexual reproduction resulting in quick population growth and sexual reproduction enabling long‐term persistence—are key components of freshwater ecosystems. Here, I studied the fitness effects of warming in Hydra oligactis, a freshwater cnidarian that reproduces asexually throughout most of the year but switches to sexual reproduction under decreasing temperatures. I exposed hydra polyps to a simulated short summer heatwave or long‐term elevated winter temperature. Since sexual development in this species is dependent on low temperature, I predicted reduced sexual investment (gonad production) and elevated asexual fitness (budding) in polyps exposed to higher temperatures. The results show a complex effect of warming on sexual fitness: While gonad number decreased in response to warming, both male and female polyps exposed to high winter temperature were capable of multiple rounds of gamete production. Asexual reproduction and survival rate, on the contrary, clearly increased in response to higher temperature, especially in males. These results predict increased population growth of H. oligactis in temperate freshwater habitats, which will likely affect the population dynamics of its main prey (freshwater zooplankton), and through that, the whole aquatic ecosystem. [ABSTRACT FROM AUTHOR]

Sponges host a wide range of cryptic biodiversity both internally and externally. This study quantified the biodiversity inhabiting, or associated with, three morphologically distinct coral reef sponges. Coelocarteria singaporensis, Coscinoderma mathewsi and Ircinia microconulosa were collected from fringing reefs at Orpheus Island, central Great Barrier Reef, across monsoonal seasons (wet and dry) and diurnal periods (morning, afternoon and night for C. singaporensis) to quantify Sponge Associated Biota (SAB). A total of 8489 SAB was sorted from 77 sponges. Twenty‐six taxa, across 3 kingdoms and 12 phyla were recorded. Sponge‐associated biota was dominated by Mollusca in all three sponge hosts (range ~ 46%–50%) but taxa were found from a number of other phyla including, Arthropoda, Annelida, Echinodermata, Cnidaria, Foraminifera and Nemertea. There was no effect of season on abundances of SAB within the three species of sponge, but there was a significant effect associated with sponge host species, driven by a higher number of SAB in C. singaporensis and I. microconulosa. The diurnal patterns of SAB within C. singaporensis showed consistent abundances of mobile invertebrate groups with molluscs, echinoderms and arthropods dominating these samples. This study also highlights the ecological role and contribution of SAB in the reef ecosystems. [ABSTRACT FROM AUTHOR]

Aim: The aim was to test trait–environment relationships in hydroids across large spatial and environmental gradients and to evaluate associations between traits, environmental variables, space and phylogeny. Location: Atlantic Ocean and adjacent polar seas. Time period: Present day. Major taxa studied: Hydrozoa. Methods: Trait–environment relationships and their spatial and phylogenetic contexts were assessed in hydroids by using a combination of a fourth‐corner test and extended‐RLQ approach, in a multivariate ordination method that uses five matrices: (1) species across sites, (2) environmental data across sites, (3) traits across species, (4) latitude and longitude for each site, and (5) phylogenetic distance among species. We based our analyses on 3680 records of 431 species distributed at 1440 sites, 16 species traits, nine environmental variables and a phylogenetic tree of the studied species. Results: Hydroid traits are significantly correlated with environmental variables and geographical space, and hydroid phylogeny is correlated with the environment and geographical space. More evidently, we observed an increased presence of larger species (taller, more branched, with greater base diameter and polysiphonic) at sites richer in nitrate and silicate, with higher dissolved oxygen, lower temperatures, lower salinities and lower current velocities. The observation of phylogenetically related species with similar traits and distributions corroborates that historical processes interact with the environment in determining community assembly and explaining patterns of distribution of species traits. Main conclusions: Several environmental variables combined affect the distribution of hydroid traits, which are also influenced by spatial and historical factors. In the first analysis of its kind for hydrozoans, we have provided an overview of how hydroids are distributed across environments according to their traits and revealed the spatial and phylogenetic components of these trait–environment relationships. [ABSTRACT FROM AUTHOR]

As fundamental components of RNA silencing, small RNA (sRNA) molecules ranging from 20 to 32 nucleotides in length have been found as potent regulators of gene expression and genome stability in many biological processes of eukaryotes. Three major small RNAs are active in animals, including the microRNA (miRNA), short interfering RNA (siRNA), and PIWI‐interacting RNA (piRNA). Cnidarians, the sister group to bilaterians, are at a critical phylogenetic node to better model eukaryotic small RNA pathway evolution. To date, most of our understanding of sRNA regulation and its potential contribution to evolution has been limited to a few triploblastic bilaterian and plant models. The diploblastic nonbilaterians, including the cnidarians, are understudied in this regard. Therefore, this review will present the current‐known small RNA information in cnidarians to enhance our understanding of the development of the small RNA pathways in early branch animals. [ABSTRACT FROM AUTHOR]

Cnidarians form a disparate phylum of animals and their diploblastic body plan represents a key step in animal evolution. Cnidarians are split into two main classes; anthozoans (sea anemones, corals) are benthic polyps, while medusozoans (hydroids, jellyfishes) generally have alternating life cycle stages of polyps and medusae. A sessile polyp is present in both groups and is widely regarded as the ancestral form of their last common ancestor. However, the nature and anatomy of the ancestral polyp, particularly of medusozoans, is controversial, owing to the divergent body plans of the extant lineages and the scarcity of medusozoan soft tissues in the fossil record. Here, we redescribe Conicula striata Luo & Hu from the early Cambrian Chengjiang biota, south China, which has previously been interpreted as a polyp, lophophorate or deuterostome. Through re-examination of the holotype and 51 exceptionally preserved specimens, we show that C. striata possessed features of both anthozoans and medusozoan polyps. A conical, annulated organic skeleton (periderm) fully encasing a polyp is found in fossil and living medusozoans, while a tubular pharynx extending from the mouth into a gut partitioned by c. 28 mesenteries, resembling the actinopharynx of anthozoans. Our phylogenetic analyses recover C. striata as a stem-group medusozoan, implying that the wealth of medusozoan diversity derived, ultimately, from an anemone-like ancestor. [ABSTRACT FROM AUTHOR]

Cnidarians are phylogenetically located near the base of the ‘tree of animals’, and their early evolution had a profound impact on the rise of bilaterians. However, the early diversity and phylogeny of this ‘lowly’ metazoan clade has hitherto been enigmatic. Fortunately, cnidarian fossils from the early Cambrian could provide key insights into their evolutionary history. Here, based on a scrutiny of the purported hyolith Burithes yunnanensis Hou et al. from the early Cambrian Chengjiang biota in South China, we reveal that this species shows characters distinct from those typical of hyoliths, not least a funnel-shaped gastrovascular system with a single opening, a whorl of tentacles surrounding the mouth, and the lack of an operculum. These characters suggest a great deviation from the original definition of the genus Burithes, and a closer affinity with cnidarians. We therefore reassign the material to a new genus: Palaeoconotuba. Bayesian inference of phylogeny based on new anatomical traits identifies a new clade, including Palaeoconotuba and Cambrorhytium, as a stem group of sessile medusozoan cnidarians that are united by the synapomorphies of developing an organic conical theca and a funnel-like gastrovascular system. This study unveils a stem lineage of medusozoans that evolved a lifelong conical theca in the early Cambrian. [ABSTRACT FROM AUTHOR]

I porpita i , which has certainly entered the Mediterranean Sea from the Atlantic Ocean or the Red Sea or possibly both of them in recent years, represents an additional illustration of the changes in Mediterranean biodiversity under the effect of the so-called process of "tropicalization". First record of Porpita porpita LINNAEUS, 1758 (Cnidaria, Hydrozoa) on the Syrian coast of the eastern Mediterranean Sea. I porpita i Linnaeus, 1758 (Class Hydrozoa Owen, 1843; Order Anthoathecata Cornelius, 1992; Family Porpitidae Goldfuss, 1818; Genus I Porpita i Lamarck, 1801; species I porpita i Linnaeus, 1758). [Extracted from the article]

Increasing heat content, salinity, and velocity of the Atlantic water masses passing northward through the Fram Strait accelerate the transition of the European Arctic toward more Atlantic state, a process referred to as Atlantification. A pronounced environmental shift leads to a poleward expansion of boreal species ranges and alters seasonal rhythms of local taxa, potentially affecting the whole food web structure. Here, we monitored a pelagic cnidarian, Aglantha digitale, commonly associated with boreal waters, throughout 12 consecutive summers (2003–2014) and along 2 branches of the West Spitsbergen Current, the main conveyor of Atlantic water to the Arctic. We documented a steady decrease in A. digitale abundance in the epipelagic waters of the European Arctic and a disproportionately larger northward advection of this jellyfish with the eastern branch of the West Spitsbergen Current compared to the western branch. Supported with modeling techniques, we found that year after year, A. digitale reproduced earlier in the southern region, thus leading to an earlier descent of the larger, more mature specimens, toward deeper waters, where they avoided our epipelagic sampling. Moreover, the prevalence of smaller jellyfish during years with record‐level water temperature and salinity (2005–2007) in the southern region of the Fram Strait indicated that a 2nd reproductive cycle may have occurred. We also showed that the northern population of A. digitale, or at least part of it, originates in the south and is advected northward with the West Spitsbergen Current. In addition, our work highlights the need to include jellyfish in zooplankton monitoring. [ABSTRACT FROM AUTHOR]

Hexangulaconulariids, an extinct family of medusozoan small shelly fossils (SSFs), were a conspicuous component of early Cambrian, shallow marine platform communities in South China. Described herein is Septuconularia crassiformis sp. nov. from Bed 5 of the Yanjiahe Formation (Cambrian Stage 2) in the Three Gorges area of Hubei Province. The new species differs from the type and only other known species, S. yanjiaheensis, in the shape of the abapical portion and in the degree of curvature of the adapertural margin. The anatomy of the apical portion of the new species is unknown. The diagnosis of the genus Septuconularia is emended and the spatio‐temporal distribution of hexangulaconulariids in South China is summarized. Finally, S. yanjiaheensis, with its slit‐like aperture and very narrow transverse cross‐section, may have been better adapted to the shallow platform environment than the broader S. crassiformis, which appears to have been less common than the type species. [ABSTRACT FROM AUTHOR]

Background: In almost all metazoans examined to this respect, the axial patterning system based on canonical Wnt (cWnt) signaling operates throughout the course of development. In most metazoans, gastrulation is polar, and embryos develop morphological landmarks of axial polarity, such as blastopore under control/regulation from cWnt signaling. However, in many cnidarian species, gastrulation is morphologically apolar. The question remains whether сWnt signaling providing the establishment of a body axis controls morphogenetic processes involved in apolar gastrulation. Results: In this study, we focused on the embryonic development of Dynamena pumila, a cnidarian species with apolar gastrulation. We thoroughly described cell behavior, proliferation, and ultrastructure and examined axial patterning in the embryos of this species. We revealed that the first signs of morphological polarity appear only after the end of gastrulation, while molecular prepatterning of the embryo does exist during gastrulation. We have shown experimentally that in D. pumila, the direction of the oral‐aboral axis is highly robust against perturbations in cWnt activity. Conclusions: Our results suggest that morphogenetic processes are uncoupled from molecular axial patterning during gastrulation in D. pumila. Investigation of D. pumila might significantly expand our understanding of the ways in which morphological polarization and axial molecular patterning are linked in Metazoa. Key Findings: Embryonic development of a non‐model hydrozoan D. pumila was thoroughly described.D. pumila gastrulates in an apolar fashion via a combination of primary and secondary delamination.Morphological polarity appears after the end of gastrulation, but molecular prepatterning exists during gastrulation.Morphogenetic processes are uncoupled from cWnt‐mediated molecular polarity during gastrulationThe direction of the primary body axis is highly robust against perturbations in cWnt activity in D. pumila. [ABSTRACT FROM AUTHOR]

Metazoans with worm‐like morphologies across diverse and disparate groups typically demonstrate motility generated by hydrostatic skeletons involving tissue layers (muscles and epithelia). Here we present representative morphological, behavioural and molecular data for parasitic cnidarians (myxozoans) that demonstrate unprecedented variation in form and function, developing as cellular hydrostats. Motile elongate plasmodia characterise a remarkable radiation of species in the genus Ceratomyxa. The vermiform plasmodia inhabit gall bladders of a range of South American freshwater fish and exhibit undulatory motility reminiscent of nematodes but achieved at the cellular level. Collective insights from ultrastructure, confocal and light microscopy along with videos depicting movements highlight key features that we propose explain the unique motility of the plasmodia. These features include cytoskeletal elements (net forming microfilaments and microtubules), a large internal vacuole, a relatively rigid outer glycocalyx and peripherally arranged mitochondria. These constituents provide collective evidence for repurposing of the cnidarian epitheliomuscular cell to support worm‐like motility at the cellular level. The apparent restriction of vermiform ceratomyxids to South American freshwaters suggests an origination via Cretaceous or Miocene marine transgressions and subsequent radiation. [ABSTRACT FROM AUTHOR]

The phylum Cnidaria is the oldest extant venomous group and is defined by the presence of nematocysts, specialized organelles responsible for venom production and delivery. Although toxin peptides and the cells housing nematocysts are distributed across the entire animal, nematocyte and venom profiles have been shown to differ across morphological structures in actiniarians. In this study, we explore the relationship between patterns of toxin expression and the ecological roles of discrete anatomical structures in Telmatactis stephensoni. Specifically, using a combination of proteomic and transcriptomic approaches, we examined whether there is a direct correlation between the functional similarity of regions and the similarity of their associated toxin expression profiles. We report that the regionalization of toxin production is consistent with the partitioning of the ecological roles of venom across envenomating structures, and that three major functional regions are present in T. stephensoni: tentacles, epidermis and gastrodermis. Additionally, we find that most structures that serve similar functions not only have comparable putative toxin profiles but also similar nematocyst types. There was no overlap in the putative toxins identified using proteomics and transcriptomics, but the expression patterns of specific milked venom peptides were conserved across RNA‐sequencing and mass spectrometry imaging data sets. Furthermore, based on our data, it appears that acontia of T. stephensoni may be transcriptionally inactive and only mature nematocysts are present in the distal portions of the threads. Overall, we find that the venom profile of different anatomical regions in sea anemones varies according to its ecological functions. [ABSTRACT FROM AUTHOR]

Up to one‐third of all described marine species inhabit coral reefs, but the future of these hyperdiverse ecosystems is insecure due to local and global threats, such as overfishing, eutrophication, ocean warming and acidification. Although these impacts are expected to have a net detrimental effect on reefs, it has been shown that some organisms such as octocorals may remain unaffected, or benefit from, anthropogenically induced environmental change, and may replace stony corals in future reefs. Despite their potential importance in future shallow‐water coastal environments, the molecular mechanisms leading to the resilience to anthropogenically induced stress observed in octocorals remain unknown. Here, we use manipulative experiments, proteomics and transcriptomics to show that the molecular toolkit used by Pinnigorgia flava, a common Indo‐Pacific gorgonian octocoral, to deposit its calcium carbonate skeleton is resilient to heat and seawater acidification stress. Sublethal heat stress triggered a stress response in P. flava but did not affect the expression of 27 transcripts encoding skeletal organic matrix (SOM) proteins. Exposure to seawater acidification did not cause a stress response but triggered the downregulation of many transcripts, including an osteonidogen homologue present in the SOM. The observed transcriptional decoupling of the skeletogenic and stress‐response toolkits provides insights into the mechanisms of resilience to anthropogenically driven environmental change observed in octocorals. [ABSTRACT FROM AUTHOR]

The algal cell wall is an important cellular component that functions in defense, nutrient utilization, signaling, adhesion, and cell–cell recognition—processes important in the cnidarian–dinoflagellate symbiosis. The cell wall of symbiodiniacean dinoflagellates is not well characterized. Here, we present a method to isolate cell walls of Symbiodiniaceae and prepare cell‐wall‐enriched samples for proteomic analysis. Label‐free liquid chromatography–electrospray ionization tandem mass spectrometry was used to explore the surface proteome of two Symbiodiniaceae species from the Great Barrier Reef: Breviolum minutum and Cladocopium goreaui. Transporters, hydrolases, translocases, and proteins involved in cell‐adhesion and protein–protein interactions were identified, but the majority of cell wall proteins had no homologues in public databases. We propose roles for some of these proteins in the cnidarian–dinoflagellate symbiosis. This work provides the first proteomics investigation of cell wall proteins in the Symbiodiniaceae and represents a basis for future explorations of the roles of cell wall proteins in Symbiodiniaceae and other dinoflagellates. [ABSTRACT FROM AUTHOR]

Mechanical properties of the skeleton of four antipatharians (the whip species Cirrhipathes anguina and Stichopathes cf. maldivensis, and the branched species Cupressopathes abies and Cupressopathes cf. pumila) living in shallow waters off the southwestern coast of Madagascar were investigated using a three‐point bending test. The Young's modulus did not differ according to species but was significantly higher in the distal segment of colonies, compared with the basal and median segments. By contrast, the flexural stiffness was significantly higher in whip species compared with branched ones, and in the whip species, flexural stiffness was higher in the basal segment compared with the other two segments, an observation consistent with a specific adaptation of the species to a strong current environment. Although both species cohabit identical flow conditions, whip species are able to maintain their stalk in vertical position, whereas branched species can readily bend over. This suggests that the specific flexural stiffness is linked to contrasting feeding strategies of species with different morphologies in a similar strong current environment. [ABSTRACT FROM AUTHOR]

Background: Metamorphosis in marine species is characterized by profound changes at the ecophysiological, morphological, and cellular levels. The cnidarian Clytia hemisphaerica exhibits a triphasic life cycle that includes a planula larva, a colonial polyp, and a sexually reproductive medusa. Most studies so far have focused on the embryogenesis of this species, whereas its metamorphosis has been only partially studied. Results: We investigated the main morphological changes of the planula larva of Clytia during the metamorphosis, and the associated cell proliferation and apoptosis. Based on our observations of planulae at successive times following artificial metamorphosis induction using GLWamide, we subdivided the Clytia's metamorphosis into a series of eight morphological stages occurring during a pre‐settlement phase (from metamorphosis induction to planula ready for settlement) and the post‐settlement phase (from planula settlement to primary polyp). Drastic morphological changes prior to definitive adhesion to the substrate were accompanied by specific patterns of stem‐cell proliferation as well as apoptosis in both ectoderm and endoderm. Further waves of apoptosis occurring once the larva has settled were associated with morphogenesis of the primary polyp. Conclusion: Clytia larval metamorphosis is characterized by distinct patterns of apoptosis and cell proliferation during the pre‐settlement phase and the settled planula‐to‐polyp transformation. Key Findings: Here, we described for the first time the dynamics process of the larva metamorphosis of the well‐established model of cnidarian Clytia hemisphaerica at the morphological and cellular scale.This fundamental descriptive work brought out that metamorphosis start before the settlement, in opposite with the usually accepted view in marine animals.At the cellular level we characterized apoptosis, proliferation and migration implicated in major transformations. One of them is the adhesive structure offset laterally, an unexpected characteristic in a cnidarian. [ABSTRACT FROM AUTHOR]

Dero digitata is the definitive oligochaete host of Henneguya ictaluri (Cnidaria: Myxobolidae), the causative agent of proliferative gill disease in U.S. farm‐raised Channel Catfish Ictalurus punctatus and hybrid catfish (Channel Catfish × Blue Catfish I. furcatus). Several studies were performed to identify optimal conditions for culturing D. digitata in the laboratory for experimental life cycle studies. The first experiments investigated the effects of temperature on D. digitata population growth. Five different growth studies were conducted, each consisting of three different temperature treatments ranging from 7°C to 32°C. Cultures were held under different temperature regimes, and D. digitata numbers were determined after 2 weeks. Dero digitata populations reared at 21–32°C had significantly higher population growth than those maintained at lower temperatures. Additional experiments investigated the effects of supplemental diets on laboratory‐reared D. digitata populations. Treatments consisted of autoclaved water that was collected from production ponds with substantial algal growth or a reservoir pond with a negligible algal bloom and maintained at ideal temperatures determined from the temperature trials (~26°C). Cultures were supplemented with three different commercially available feeds designed for bottom‐feeding ornamental fish. Significantly larger numbers and greater reproductive rates, taken as an indirect measure of population fitness, were observed in D. digitata cultured in autoclaved pond water supplemented with algal wafers containing 29.0% minimum (min.) crude protein, 7.0% min. crude fat, 6.0% maximum (max.) crude fiber, 9.0% max. moisture, and 0.8% min. phosphorus. A final experiment showed that weekly water exchanges resulted in greater population growth of D. digitata relative to culture in nonexchanged water. This work optimizes the laboratory propagation of D. digitata and will facilitate life cycle studies and controlled experiments establishing developmental timelines and host–parasite interactions of H. ictaluri, similar to other myxozoan parasites. [ABSTRACT FROM AUTHOR]

Summary: Corals are colonized by symbiotic microorganisms that profoundly influence the animal's health. One noted symbiont is a single‐celled alga (in the dinoflagellate family Symbiodiniaceae), which provides the coral with most of its fixed carbon. Thermal stress increases the production of reactive oxygen species (ROS) by Symbiodiniaceae during photosynthesis. ROS can both damage the algal symbiont's photosynthetic machinery and inhibit its repair, causing a positive feedback loop for the toxic accumulation of ROS. If not scavenged by the antioxidant network, excess ROS may trigger a signaling cascade ending with the coral host and algal symbiont disassociating in a process known as bleaching. We use Exaiptasia diaphana as a model for corals and constructed a consortium comprised of E. diaphana–associated bacteria capable of neutralizing ROS. We identified six strains with high free radical scavenging (FRS) ability belonging to the families Alteromonadaceae, Rhodobacteraceae, Flavobacteriaceae and Micrococcaceae. In parallel, we established a consortium of low FRS isolates consisting of genetically related strains. Bacterial whole genome sequences were used to identify key pathways that are known to influence ROS. [ABSTRACT FROM AUTHOR]

Wnt ligands are key signaling molecules in animals, but little is known about the evolutionary dynamics and mode of action of the WntA orthologs, which are not present in the vertebrates or in Drosophila. Here we show that the WntA subfamily evolved at the base of the Bilateria + Cnidaria clade, and conserved the thumb region and Ser209 acylation site present in most other Wnts, suggesting WntA requires the core Wnt secretory pathway. WntA proteins are distinguishable from other Wnts by a synapomorphic Iso/Val/Ala216 amino‐acid residue that replaces the otherwise ubiquitous Thr216 position. WntA embryonic expression is conserved between beetles and butterflies, suggesting functionality, but the WntA gene was lost three times within arthropods, in podoplean copepods, in the cyclorrhaphan fly radiation, and in ensiferan crickets and katydids. Finally, CRISPR mosaic knockouts (KOs) of porcupine and wntless phenocopied the pattern‐specific effects of WntA KOs in the wings of Vanessa cardui butterflies. These results highlight the molecular conservation of the WntA protein across invertebrates, and imply it functions as a typical Wnt ligand that is acylated and secreted through the Porcupine/Wntless secretory pathway. HIGHLIGHTS: WntA was lost in vertebrates and three arthropod lineages includingThe WntA thumb region and acylation site are conservedDisruptions of Porcupine (Porc) and Wntless (Wls) recapitulate WntA knockouts in butterfly wingsWntA requires Porc and Wls for acylation and trafficking [ABSTRACT FROM AUTHOR]

Box jellyfish have an elaborate visual system and perform advanced visually guided behaviors. However, the rhopalial nervous system (RNS), believed to be the main visual processing center, only has 1000 neurons in each of the four eye carrying rhopalia. We have examined the detailed structure of the RNS of the box jellyfish Tripedalia cystophora, using immunolabeling with antibodies raised against four putative neuropeptides (T. cystophora RFamide, VWamide, RAamide, and FRamide). In the RNS, T. cystophora RF‐, VW‐, and RAamide antibodies stain sensory neurons, the pit eyes, the neuropil, and peptide‐specific subpopulations of stalk‐associated neurons and giant neurons. Furthermore, RFamide ir+ neurites are seen in the epidermal stalk nerve, whereas VWamide antibodies stain the gastrodermal stalk nerve. RFamide has the most widespread expression including in the ring and radial nerves, the pedalium nerve plexus, and the tentacular nerve net. RAamide is the putative neurotransmitter in the motor neurons of the subumbrellar nerve net, and VWamide is a potential marker for neuronal differentiation as it is found in subpopulations of undifferentiated cells both in the rhopalia and in the bell. The results from the FRamide antibodies were not included as only few cells were stained, and in an unreproducible way. Our studies show hitherto‐unseen details of the nervous system of T. cystophora and allowed us to identify specific functional groups of neurons. This identification is important for understanding visual processing in the RNS and enables experimental work, directly addressing the role of the different neuropeptides in vision. [ABSTRACT FROM AUTHOR]

Facultative sexuality combines clonal propagation with sexual reproduction within a single life cycle. Clonal propagation enables quick population growth and the occupancy of favorable habitats. Sex, on the contrary, results in the production of offspring that are more likely to survive adverse conditions (such as the resting eggs of many freshwater invertebrates). In seasonal environments, the timing of sex is often triggered by environmental cues signaling the onset of winter (e.g., temperature drop or changes in photoperiod). Organisms switching to sex to produce resting eggs under these conditions face a trade‐off: Responding too early to an environmental cue increases the chances of missing out in clonal propagation, while having a delayed response to deteriorating conditions entails the risk of parental mortality before sexual reproduction could be completed. To mitigate these risks, increased sensitivity toward environmental cues with the onset of the winter might be an adaptive strategy. To test this hypothesis, we investigated sexual propensity and time to gonadogenesis in clonal strains derived from spring‐ and autumn‐collected polyps of Hydra oligactis, a facultatively sexual freshwater cnidarian where sex only occurs prior to the onset of winter. We show that autumn‐collected individuals and their asexual offspring have a higher propensity for sex and require less time for gonad development compared with strains established from spring‐collected individuals that were kept under similar conditions in the laboratory. To see whether the above results can be explained by phenotypic plasticity in sexual readiness, we exposed cold‐adapted laboratory strains to different lengths of warm periods. We found that sexual propensity increases with warm exposure. Our results suggest that reciprocal cold and warm periods are required for sex induction in H. oligactis, which would ensure proper timing of sex in this species. Increased sensitivity to environmental deterioration might help maximize fitness in environments that have both a predictable (seasonal) and an unpredictable component. [ABSTRACT FROM AUTHOR]

Modern systematics integrating molecular and morphological data has greatly improved our understanding of coral evolutionary relationships during the last two decades and led to a deeply revised taxonomy of the order Scleractinia. The family Merulinidae (Cnidaria: Scleractinia) was recently subjected to a series of revisions following this integrated approach but the phylogenetic affinities of several genera ascribed to it remain unknown. Here, we partially fill this gap through the study of 89 specimens belonging to all 10 valid species from four genera (Caulastraea, Erythrastrea, Oulophyllia and Dipsastraea) collected from 14 localities across the Indo‐Pacific realm. Four molecular loci (histone H3, COI, ITS and IGR) were sequenced, and a total of 44 skeletal morphological characters (macromorphology, micromorphology and microstructure) were analysed. Molecular phylogenetic analyses revealed that the phaceloid Caulastraea species are split into two distinct lineages. A species previously ascribed to the genus Dipsastraea, Dipsastraea maxima, is also recovered in one on these lineages. Furthermore, Erythrastrea is nested within Oulophyllia. The molecular reconstructions of evolutionary relationships are further corroborated by multiscale morphological evidence. To resolve the taxonomy of these genera, Astraeosmilia is resurrected to accommodate Astraeosmilia connata, Astraeosmilia curvata, Astraeosmiliatumida and Astraeosmilia maxima, with Caulastraea retaining Caulastraeafurcata and Caulastraeaechinulata. Based on the examination of type material, Erythrastrea flabellata is considered an objective synonym of Lobophyllia wellsi, which is transferred to Oulophyllia following the obtained morpho‐molecular results. This work further confirms that an integrated morpho‐molecular approach based on a rigorous phylogenetic framework is fundamental for an objective classification that reflects the evolutionary history of scleractinian corals. [ABSTRACT FROM AUTHOR]

Patterns of population biology and community structure can be studied by looking closely at the ontogeny and reproductive biology of reef‐building organisms. This knowledge is particularly important for Caribbean octocorals, which seem to be more resilient to long‐term environmental change than scleractinian corals and provide some of the same ecological services. We monitored the development of the black sea rod, Plexaura homomalla, a common, widely distributed octocoral on shallow Caribbean reefs, from eggs to three‐polyp colonies over the course of 10 weeks. Gametes were collected ex situ on St. John, U.S. Virgin Islands, during spawning events that occurred 3–6 days after the July full moon. Cleavage started 3.0 hr after fertilization and was holoblastic, equal, and radial. Embryos were positively buoyant until becoming planulae at 3 days after fertilization. Planulae were competent to settle 4 days after fertilization. Symbiodiniaceae began infecting polyps ~8 days after fertilization. Overall, development was typical for Caribbean octocorals, except for an increase in the number of embryos between 3.5 and 6.0 hr after fertilization. [ABSTRACT FROM AUTHOR]

Our understanding of how sea anemones reproduce in the equatorial Central Indo‐Pacific region remains poor compared to other marine regions. Here we report the gametogenic cycles of Phymanthus pinnulatus, a zooxanthellate sea anemone found throughout the Indo‐Pacific tropics. Observations were based on 41 individuals collected in Singapore. We found P. pinnulatus to be gonochoric, with an equal sex ratio of 1:1. Phases of oogenesis and spermatogenesis were detailed for the first time in P. pinnulatus, and were consistent with phases in other actiniarians. Females with pedal disc diameters <10 mm were found to asynchronously produce oocytes. We also found that trophonemata were associated with both oocytes and spermaries during gametogenesis. In Singapore, the periods during which gametes matured in each sex of P. pinnulatus appeared to overlap. We were unable distinguish whether spawning was annual or continuous in P. pinnulatus. Our observations on the occurrence of maturing and matured gametes in P. pinnulatus were similar to those reported for other species within the Central Indo‐Pacific. It also coincided with the multispecies spawning of scleractinian corals in Singapore. This study contributes to the growing body of work focused on the biology of tropical actiniarians in the Central Indo‐Pacific region. [ABSTRACT FROM AUTHOR]

Silver nanoparticles (Ag‐NPs) streamed into aquatic environments are chemically transformed into various forms, and one of the predominant forms is silver sulfide NPs (Ag2S‐NPs). Because of the lower dissolution rate of silver ions (Ag+), the toxicity of Ag2S‐NPs could be lower than that of Ag‐NPs. However, the toxicity of Ag2S‐NPs has been observed to be restored under oxidative or acidic conditions. In the present study, 4 aquatic organisms, Pseudokirchneriella subcapitata (algae), Daphnia magna (crustacean), Danio rerio (fish), and Hydra vulgaris (cnidarian), were exposed to Ag2S‐NPs transformed from Ag‐NPs using Na2S under anoxic conditions; and acute toxicity was evaluated. The acute toxicity of Ag2S‐NPs was rarely observed in algae, crustaceans, and fish, whereas it was significantly restored in cnidarians. Although the dissolution rate was low in the medium exposed to Ag2S‐NPs, high Ag+ was detected in H. vulgaris. To understand the mechanisms of Ag2S‐NP toxicity in cnidarians, transcriptional profiles of H. vulgaris exposed to Ag‐NPs, Ag2S‐NPs, and AgNO3 were analyzed. As a result, most of the genes that were significantly changed in the Ag2S‐NPs group were also found to be significantly changed in the AgNO3 group, indicating that the toxicity of Ag2S‐NPs was caused by Ag+ dissolved by the acidic condition in the gastrovascular cavity of H. vulgaris. This finding is the first in an aquatic organism and suggests the need to reconsider the stability and safety of Ag2S‐NPs in the aquatic environment. Environ Toxicol Chem 2021;40:1662–1672. © 2021 SETAC [ABSTRACT FROM AUTHOR]

Complex biological traits often originate by integrating previously separate parts, but the organismal functions of these precursors are challenging to infer. If we can understand the ancestral functions of these precursors, it could help explain how they persisted and how they facilitated the origins of complex traits. Animal eyes are some of the best studied complex traits, and they include many parts, such as opsin‐based photoreceptor cells, pigment cells, and lens cells. Eye evolution is understood through conceptual models that argue these parts gradually came together to support increasingly sophisticated visual functions. Despite the well‐accepted logic of these conceptual models, explicit comparative studies to identify organismal functions of eye precursors are lacking. Here, we investigate how precursors functioned before they became part of eyes in Cnidaria, a group formed by sea anemones, corals, and jellyfish. Specifically, we test whether ancestral photoreceptor cells regulated the discharge of cnidocytes, the expensive single‐use cells with various functions including prey capture, locomotion, and protection. Similar to a previous study of Hydra, we show an additional four distantly related cnidarian groups discharge significantly more cnidocytes when exposed to dim blue light compared with bright blue light. Our comparative analyses support the hypothesis that the cnidarian ancestor was capable of modulating cnidocyte discharge with light, which we speculate uses an opsin‐based phototransduction pathway homologous to that previously described in Hydra. Although eye precursors might have had other functions like regulating timing of spawning, our findings are consistent with the hypothesis that photoreceptor cells which mediate cnidocyte discharge predated eyes, perhaps facilitating the prolific origination of eyes in Cnidaria. [ABSTRACT FROM AUTHOR]

The Strait of Sicily (SoS) is a key area in the Central Mediterranean Sea characterized by high biodiversity and demersal fisheries productivity. Further, it is traditionally considered the main biogeographic boundary between the Western and Eastern basins of the Mediterranean. Due to the poor knowledge on the benthos composition and distribution in this area, we created the first inventory of megazoobenthos recorded on the trawlable soft bottoms of the North‐Western SoS. Samples were collected by bottom trawl surveys between 2003 and 2013 within a depth range of 10–800 m. Overall, 374 taxa with 358 species, belonging to Porifera, Cnidaria, Nemertea, Rotifera, Brachiopoda, Bryozoa, Sipuncula, Annelida, Mollusca, Arthropoda, Echinodermata and Chordata phyla, were found. In addition, the biogeographic affinity of megazoobenthos collected in the SoS to species vulnerable to trawl survey found in other zones of the Central Mediterranean was investigated. Excluding the North Adriatic and the Strait of Messina, moderate affinity values have been recorded within all the biogeographic zones. The benthos species of the North‐Western SoS presented the highest affinity with those of the North Tyrrhenian and Ligurian Sea (about 90% of species in common). However, our results show high similarity with species composition of the South‐Eastern SoS/South Ionian, North Ionian and Central Adriatic (about 80% of species in common). Our study confirms the role as biogeographic transition zone of the SoS for the Mediterranean biota. Furthermore, the lower affinity with native species of the South‐Eastern SoS and the absence of Lessepsian species suggest that the cold waters (due to the permanent up‐welling) off the southern coasts of Sicily may act as thermal barrier for regulating species exchange between the Eastern and Western basins. Some concerns about this role of the northern sector of the SoS were discussed in the light of current climate change. [ABSTRACT FROM AUTHOR]

Body size has fundamental impacts on animal ecology and physiology but has been strongly influenced by recent climate change and human activities, such as size‐selective harvesting. Understanding the ecological and life history consequences of body size has proved difficult due to the inseparability of direct effects of body size from processes connected to it (such as growth rate and individual condition). Here, we used the cnidarian Hydra oligactis to directly manipulate body size and understand its causal effects on reproduction and senescence. We found that experimentally reducing size delayed sexual development and lowered fecundity, while post‐reproductive survival increased, implying that smaller individuals can physiologically detect their reduced size and adjust life history decisions to achieve higher survival. Our experiment suggests that ecological or human‐induced changes in body size will have immediate effects on life history and population dynamics through a growth‐independent link between body size, reproduction and senescence. [ABSTRACT FROM AUTHOR]

The developmental and evolutionary principles of coloniality in marine animals remain largely unexplored. Although many common traits have evolved independently in different groups of colonial animals, questions about their significance for colonial life histories remain unanswered. In 2018 (Nov. 25 ‐ Dec. 8), the inaugural course on the Evolution of Coloniality and Modularity took place at the Center for Marine Biology of the University of São Paulo (CEBIMAR‐USP), Brazil. During the intensive two‐week graduate‐level course, we addressed some of the historical ideas about animal coloniality by focal studies in bryozoans, tunicates, cnidarians, and sponges. We discussed many historical hypotheses and ways to test these using both extant and paleontological data, and we carried direct observations of animal colonies in the different phyla to address questions about coloniality. We covered topics related to multi‐level selection theory and studied colonial traits, including modular miniaturization, polymorphism, brooding, and allorecognition. Course participants carried out short research projects using local species of animals to address questions on allorecognition and regeneration in ascidians and sponges, fusion and chimerism in anthoathecate hydrozoans, and evolution of polymorphism in bryozoans. Although many questions remain unanswered, this course served as a foundation to continue to develop a developmental and evolutionary synthesis of clonal and modular development in colonial marine organisms. [ABSTRACT FROM AUTHOR]

Despite considerable interest in the effects of evolutionary conflict in colonies of social insects, relatively little attention has been paid to this issue in clonal animals with modular construction, such as colonial ascidians, bryozoans, and cnidarians. These colonial animals are structural individuals, subdivided into repeated morphological modules, which can individually acquire, process, and share resources. While size‐related selection favors colony formation, evolutionary conflicts remain a potent obstacle to such cooperation. These conflicts can occur at several levels and must be mediated for cooperation to emerge. Module‐level conflicts potentially result in coalitions of genetically similar modules failing to share resources or monopolizing reproduction. Mediation occurs by a number of mechanisms including: (a) a single‐module bottleneck at the initiation of colony formation, (b) allorecognition that limits colony fusion to close kin, (c) development of new modules from connective tissue, (d) synchronization of module budding, (e) programmed module death, (f) terminal differentiation of reproductive modules, and (g) architectural constraints. Effective mediation of module‐level conflicts, however, may in some cases contribute to cell‐level conflicts. Animal colonies typically have multipotent stem cells, and genetically variant stem cells can potentially monopolize gamete formation. Limiting colony fusion to close kin may not eliminate such conflict. Finally, in at least some taxa an association between photosymbiosis and coloniality is found. Allocation of photosynthate can lead to host‐symbiont conflicts that can be mediated by housing symbionts intracellularly and using chemiosmotic mechanisms to detect defectors. Colonial animals thus serve as a living laboratory of evolutionary conflict and its mediation. Research Highlights: Colonial animals are a living laboratory of evolutionary conflict and its mediation. These themes are explored at the level of modules, cells, and intracellular symbionts. Understanding the synergisms and antagonisms of selection at these various levels better illuminates the natural history of colonial animals. [ABSTRACT FROM AUTHOR]

The regenerative capacity of cnidarians plays an essential role in the maintenance and restoration of coral reef ecosystems by allowing faster recovery from disturbances and more efficient small‐scale dispersal. However, in the case of invasive species, this property may contribute to their dispersal and success in nonnative habitats. Given that four Indo‐Pacific members of the coral genus Tubastraea have invaded the Atlantic, here we evaluated the ability of three of these species (Tubastraea coccinea, Tubastraea diaphana, and Tubastraea micranthus) to regenerate from fragments of undifferentiated coral tissue to fully functional polyps in response to differences in food supply and fragment size. For comparative purposes, another colonial dendrophylliid (Dendrophyllia sp.) was included in the analyses. All dendrophylliids displayed regenerative ability and high survival rates that were independent of whether or not food was supplied or fragment size. However, regeneration rates varied between species and were influenced by fragment size. Temporal expression of key genes of the regenerative process (Wnt and FGF) was profiled during whole‐body regeneration of T. coccinea, suggesting a remarkable regenerative ability of T. coccinea that points to its potential use as a laboratory model for the investigation of regeneration in colonial calcified anthozoans. Research Highlights: All invasive Tubastraea spp. in the Atlantic and Dendrophyllia sp. were able to whole‐body regeneration. Wnt and FGF ligands are expressed during this process. Regeneration of dendrophylliids is metabolically more demanding for smaller than for larger colony fragments. [ABSTRACT FROM AUTHOR]

Many colonial marine animals care for embryos by brooding them on or in their bodies. For brooding to occur, features of the animals must allow it, and brooding must be at least as advantageous as releasing gametes or zygotes. Shared features of diverse colonial brooders are suspension feeding and a body composed of small modules that are indefinitely repeated and can function semi‐autonomously, such as polyps or zooids. Suspension feeding permits capture of sperm for fertilization of ova that are retained by the parent. Distribution of broods among numerous small polyps, zooids, or other small modules facilitates supply of oxygen to embryos that are retained and protected by the parent. Brooding increases survival of offspring, controls dispersal, and can provide other developmental advantages. Colonial ascidians, pterobranch hemichordates, and entoprocts brood; most bryozoans and many colonial cnidarians brood. An unanswered question is why so many colonial anthozoans do not brood. Sponges share with colonies capacities for capturing sperm and separating numerous retained embryos yet many do not brood. Hypotheses for nonbrooding by colonies and sponges necessarily must apply to particular taxa. Few have been tested. Research Highlights: Most colonial marine invertebrates brood their offspring. Features that permit their brooding are suspension feeding, which enables females to capture sperm from males, and distribution of embryos among small modules, which enhances oxygen supply to developing offspring. [ABSTRACT FROM AUTHOR]

In the current context of climate change, benthic cnidarians of the genus Palythoa have been suggested to be resistant owing to their intrinsic biological characteristics. In tropical regions, some species are currently proliferating in areas where environmental conditions are less suitable for other organisms, even replacing hard coral ecosystems.Considering their tropical affinities, phase‐shifts towards Palythoa‐dominated areas could become more frequent in future climate change scenarios, leading to changes in ecosystem organization. The aim of this study was to evaluate the effect of climate change stressors in two common Palythoa spp. with different habitat affinities within a subtropical region, and the effect upon their predator–prey interactions.The results of this experimental study demonstrated that colonies of P. aff. clavata and P. caribaeorum were significantly affected by exposure to temperature and pH conditions predicted for 2100 in the Canary Islands, during 62 days.Despite zoantharians' lack of carbonate in their body wall, Palythoa spp. were most affected in their growth rates by lowered pH, and colonies significantly decreased in weight and size. Although all colonies exhibited symptoms of bleaching at high temperature, a reduction in chlorophyll content was also observed at low pH.Predation by Platypodiella picta crabs decreased on P. aff. clavata exposed to acidic conditions, which may compensate for the lowered ecological performance of the species in these climate change conditions. In contrast, P. picta was able to actively feed on P. caribaeorum colonies regardless of the experimental conditions.Despite being suggested as winner species in a climate change scenario, our study demonstrated that low pH negatively impacted Palythoa spp. survival. If the species are not able to acclimatize to the new conditions, changes in their populations may be expected, although their magnitude could be ameliorated by means of a decrease in predation rates. [ABSTRACT FROM AUTHOR]

Aim: Global anthropogenic changes have altered biogeography and phenology of marine populations, thereby promoting a spatial reconfiguration in the functioning of marine ecosystems. Among these changes, massive proliferations of jellyfish in temperate latitudes warn of potential alterations in biogeochemical fluxes, ecosystems' structure and assets, and the services they provide to human welfare. Understanding driving factors shaping large‐scale patterns of jellyfish proliferations is a pressing need in global ecology and sustainability science. Using a comprehensive dataset of the largest blooming scyphomedusae in southern European seas we test, over broad space–time scales, current hypotheses relating jellyfish dynamics to warming and eutrophication. Location: Southern European seas. Time period: 1875–2019. Major taxa studied: Rhizostoma pulmo. Methods: We have gathered historical and contemporaneous records of R. pulmo from the Mediterranean and Black Seas over the last two centuries (7,359 records). Generalized statistical models were used to assess the influence of thermal (latitudinal) and productivity (longitudinal) gradients on the biogeographical patterns, and the species' phenology at large and regional scales. Results: Rhizostoma pulmo abundance exhibited an enhanced magnitude and frequency in recent decades, concurrently with positive temperature anomalies. We found that the latitudinal temperature gradient, but not productivity, shaped long‐term bloom intensity and biogeographical patterns of the species. Our analysis further uncovered a significant effect of the interannual variability of spring temperature on the species' phenology over the period 2008–2018, with warmer springs favouring an earlier start (c. 3 months) and a longer duration (from 5 to 7 months) of jellyfish season. Main conclusions: Among the current hypotheses linking jellyfish changes with anthropogenic disturbances, only the warming‐based hypothesis gained support over wide space–time scales, while the eutrophication‐based hypothesis mainly applied at local scales. Hence, biogeographical patterns of R. pulmo are shaped by the latitudinal temperature gradient, while the species bloom dynamics echo variations in ecoregion thermal regimes. [ABSTRACT FROM AUTHOR]

Environmental change, including global warming and chemical pollution, can compromise cnidarian‐(e.g., coral‐) dinoflagellate symbioses and cause coral bleaching. Understanding the mechanisms that regulate these symbioses will inform strategies for sustaining healthy coral–reef communities. A model system for corals is the symbiosis between the sea anemone Exaiptasia pallida (common name Aiptasia) and its dinoflagellate partners (family Symbiodiniaceae). To complement existing studies of the interactions between these organisms, we examined the impact of menthol, a reagent often used to render cnidarians aposymbiotic, on the dinoflagellate Breviolum minutum, both in culture and in hospite. In both environments, the growth and photosynthesis of this alga were compromised at either 100 or 300 µM menthol. We observed reduction in PSII and PSI functions, the abundances of reaction‐center proteins, and, at 300 µM menthol, of total cellular proteins. Interestingly, for free‐living algae exposed to 100 µM menthol, an initial decline in growth, photosynthetic activities, pigmentation, and protein abundances reversed after 5–15 d, eventually approaching control levels. This behavior was observed in cells maintained in continuous light, but not in cells experiencing a light–dark regimen, suggesting that B. minutum can detoxify menthol or acclimate and repair damaged photosynthetic complexes in a light‐ and/or energy‐dependent manner. Extended exposures of cultured algae to 300 µM menthol ultimately resulted in algal death. Most symbiotic anemones were also unable to survive this menthol concentration for 30 d. Additionally, cells impaired for photosynthesis by pre‐treatment with 300 µM menthol exhibited reduced efficiency in re‐populating the anemone host. [ABSTRACT FROM AUTHOR]

All metazoans are in fact holobionts, resulting from the association of several organisms, and organismal adaptation is then due to the composite response of this association to the environment. Deciphering the mechanisms of symbiont acquisition in a holobiont is therefore essential to understanding the extent of its adaptive capacities. In cnidarians, some species acquire their photosynthetic symbionts directly from their parents (vertical transmission) but may also acquire symbionts from the environment (horizontal acquisition) at the adult stage. The Mediterranean snakelocks sea anemone, Anemonia viridis (Forskål, 1775), passes down symbionts from one generation to the next by vertical transmission, but the capacity for such horizontal acquisition is still unexplored. To unravel the flexibility of the association between the different host lineages identified in A. viridis and its Symbiodiniaceae, we genotyped both the animal hosts and their symbiont communities in members of host clones in five different locations in the North Western Mediterranean Sea. The composition of within‐host–symbiont populations was more dependent on the geographical origin of the hosts than their membership to a given lineage or even to a given clone. Additionally, similarities in host–symbiont communities were greater among genets (i.e. among different clones) than among ramets (i.e. among members of the same given clonal genotype). Taken together, our results demonstrate that A. viridis may form associations with a range of symbiotic dinoflagellates and suggest a capacity for horizontal acquisition. A mixed‐mode transmission strategy in A. viridis, as we posit here, may help explain the large phenotypic plasticity that characterizes this anemone. [ABSTRACT FROM AUTHOR]