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The life cycle of the common ancestor of Metazoa is a widely debated topic in EvoDevo. This is intimately linked to a number of questions, such as how the larva appeared in the metazoan life cycle and which larval form can be considered ancestral. To approach these questions, we can analyse the life cycles and larval forms of Cnidaria, the basal metazoans that form a sister group to the Bilateria. Almost all cnidarians have a pelagic larva in their life cycle. These larvae are commonly referred to as "planula," with few exceptions. The planula is a ciliated lecithotrophic larva with epithelial ectoderm and endoderm, a gastric cavity, and an elongated body. The review examines whether the larvae of various Cnidaria fit this description and explores which larval form is ancestral for different cnidarian taxa. It also highlights the enormous diversity of cnidarian larvae, which is still underestimated, and infers the relationship between the evolution of life cycles, reproductive patterns, and larval forms in various phylogenetic groups of cnidarians. [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]

The genus Aurelia is one of the most extensively studied within the class Scyphozoa. However, much of the research was historically attributed to the species Aurelia aurita (Linnaeus, 1758) before the recognition of its taxonomic complexity. Initially considered cosmopolitan and globally distributed, recent phylogenetic analysis has challenged this assumption. Consequently, the current distribution of species within the genus Aurelia and the processes that led to this distribution remain largely unexplored. After genetically confirming that the species traditionally present in the Mar Menor coastal lagoon in the southwestern Mediterranean corresponds to A. solida, we compiled data on the locations where moon jellyfish species have been genetically identified and mapped these coordinates to the geological period when the genus Aurelia diverged from other scyphozoan genera. We propose two hypotheses to explain the disjunct distribution of certain species. The first one assumes recent human-mediated introductions, while the second posits an absence of introductions. Both hypotheses, supported by fossil and historical records, suggest a Paleo-Tethys origin of the genus Aurelia. Migration from this area explains most of the genus's current distribution without human intervention, being the Mediterranean Sea, where A. solida should be considered autochthonous, part of their natural distribution range. [ABSTRACT FROM AUTHOR]

The phosphorus content in the dry matter of modern-day Cnidarians (Hydrozoa, Scyphozoa and Anthozoa) collected in the different parts of the world's oceans ranges from 0.14 to 1.3% wt. Nektonic Cnidarians can form major aggregations in marine basins and should therefore be regarded as an important component of phosphorus flux into sediment. Seventy-five per cent of the Ediacaran fossils were interpreted as the moulds of soft-bodied organisms resembling modern-day Cnidaria. Therefore, ancient Cnidarians in the Ediacaran epeiric basins could be a source of phosphorus during the deposition of the earliest sedimentary phosphorites. [ABSTRACT FROM AUTHOR]

Scyphozoan jellyfish in Icelandic waters have received limited attention, despite apparent recent increases in blooms and changes in the regional oceanographic setting. The objectives of this study were to describe the species composition, abundance, phenology, and growth of scyphomedusae around Iceland and explore changes by comparing our findings with reports from the 1930s. Specimens were collected with a Bongo net in five regions around Iceland in the spring, summer, and autumn of 2008. Three jellyfish species were collected in the study, Aurelia aurita, followed by Cyanea capillata, and C. lamarckii. In the western and northwestern parts of Iceland, A. aurita abundance was highest in spring and summer, whereas in the North and East, abundances were highest in autumn. Cyanea capillata was not encountered in the Southwest, but in the west, Northwest, and North. There, numbers were highest in spring, whereas in the East, abundance was highest in autumn. Clockwise coastal current dispersal and regional interconnectivity are indicated. Weight-specific growth rates varied between 7.0 and 8.5% d−1 for A. aurita and 11.1 and 15.7% d−1 for C. capillata and are comparable to rates from often food-limited ecosystems at temperate latitudes. Presented evidence suggests that ephyrae and small medusae appear earlier in the season and in previously (in the 1930s) not occupied regions, while some regions (Southwest for C. capillata) were not populated anymore. [ABSTRACT FROM AUTHOR]

Background: Living organisms face ubiquitous pathogenic threats and have consequently evolved immune systems to protect against potential invaders. However, many components of the immune system are physiologically costly to maintain and engage, often drawing resources away from other organismal processes such as growth and reproduction. Evidence from a diversity of systems has demonstrated that organisms use complex resource allocation mechanisms to manage competing needs and optimize fitness. However, understanding of resource allocation patterns is limited across taxa. Cnidarians, which include ecologically important organisms like hard corals, have been historically understudied in the context of resource allocations. Improving understanding of resource allocation-associated trade-offs in cnidarians is critical for understanding future ecological dynamics in the face of rapid environmental change. Methods: Here, we characterize trade-offs between constitutive immunity and reproduction in the facultatively symbiotic coral Astrangia poculata. Male colonies underwent ex situ spawning and sperm density was quantified. We then examined the effects of variable symbiont density and energetic budget on physiological traits, including immune activity and reproductive investment. Furthermore, we tested for potential trade-offs between immune activity and reproductive investment. Results: We found limited associations between energetic budget and immune metrics; melanin production was significantly positively associated with carbohydrate concentration. However, we failed to document any associations between immunity and reproductive output which would be indicative of trade-offs, possibly due to experimental limitations. Our results provide a preliminary framework for future studies investigating immune trade-offs in cnidarians. [ABSTRACT FROM AUTHOR]

Planktonic lifestyle of polyps in representatives of Margelopsidae are very different from all other species in the hydrozoan clade Aplanulata. Their evolutionary origin and phylogenetic position have been the subject of significant speculation. A recent molecular study based only on COI data placed Margelopsidae as a sister group to all Aplanulata, an unexpected result because margelopsid morphology suggests affiliation with Tubulariidae or Corymorphidae. Here we used multigene analyses, including nuclear (18S rRNA and 28S rRNA) and mitochondrial (16S rRNA and COI) markers of the hydroid stage of the margelopsid species Margelopsis haeckelii and the medusa stage of Margelopsis hartlaubii to resolve their phylogenetic position with respect to other hydrozoans. Our data provide strong evidence that M. haeckelii, the type species of Margelopsis, is a member of the family Corymorphidae. In contrast, M. hartlaubii is sister to Plotocnide borealis, a member of Boreohydridae. These results call into question the validity of the genus Margelopsis and the family Margelopsidae. The systematic position of M. haeckelii is discussed in light of the phylogeny of Corymorphidae. [ABSTRACT FROM AUTHOR]

Purpose: The motive of the present study was to investigate incidences of myxozoan parasite infection in commercially important fishes and their characterization using morphological attributes and molecular approach. Methods: The specimens of cultured Cirrhinus mrigala were sampled and various organs were examined. The plasmodia were detected on the scales. The identification of species was based on the myxospore morphology and 18S rDNA sequence analyses. For phylogenetic analysis, maximum likelihood (ML) and Bayesian inference (BI) methods were employed. The SEM and histological studies were performed to assess the damage to the scales. Results: The infected fishes had white patches on the scales and red haemorrhagic lesions on the skin. The plasmodia of Myxobolus coriumicus n. sp. were located on the dorsal surface of the scale towards its exposed part. SEM study indicated that lepidonts were damaged in the infected scales. The myxospores were spherical in shape, 9.0–10.0 × 8.0–9.0 μ m in size, with two ovoid equal polar capsules 3.13–4.0 × 2.03–2.33 μ m in size, having 4–5 sutural edge markings at the posterior-lateral margins of the shell valves and binucleated sporoplasm. BLAST search based on 18S rDNA revealed 93.87% sequence similarity with M. rewensis, (MZ230381). The prevalence of infection was 6.3% and Scale Plasmodium Index (SPI) was 3 indicating heavy infection. Conclusion: Morpho-molecular data generated during this study enables us to conclude that the present species, M. coriumicus n. sp. infecting scales of C. mrigala is new to the science causing significant damage to the scales. [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]

Eirene ceylonensis, a hydrozoan jellyfish species with a complex polymorphic life cycle, is widely distributed in the Chinese coastal sea. In this study, we conducted sequencing and analysis of the first complete mitochondrial genome of E. ceylonensis, obtained from the coastal sea of Qinhuangdao, China. The linear mitochondrial genome is 14,997 bp in length with the overall AT content being 72.8%, encoding 13 protein-coding genes (PCGs), two transfer RNA (tRNA) genes (tRNA-Met and tRNA-Trp) and two ribosomal RNA (rRNA) genes (rrnS and rrnL). Phylogenetic analysis of 13 PCGs suggests that the E. ceylonensis is closely related to Laomedea flexuosa. The availability of the complete mitochondrial genome of E. ceylonensis will be useful for studying the evolutionary relationships of hydrozoan jellyfish species. [ABSTRACT FROM AUTHOR]

New individuals of Porpita porpita were detected along the Italian coasts of the Mediterranean Sea. In recent years, due to warming Mediterranean waters, the species has spread even further. This observation opens new horizons for further reports of this species in the Ionian and Tyrrhenian Seas of Italy.

Many metazoans contain molecules capable of fluorescence, the absorption and re-emission of light. Since the anatomical distribution, or patterning, of these molecules is variable across taxa, patterns of fluorescence may serve as a powerful diagnostic tool in taxonomy and ecology. However, species-specific fluorescence patterns among marine invertebrates are poorly understood. Here, we show that hydrozoans have diverse fluorescence patterns, which may result from molecules that are produced intrinsically or obtained from dietary sources. We surveyed hydrozoans including siphonophores, hydromedusae, and hydroids across 5 orders from pelagic and benthic marine environments in Bocas del Toro, Panama. Our findings show that fluorescence patterns are highly prevalent and may vary across hydrozoan species and throughout development. Most of the examined hydrozoan taxa exhibited some form of fluorescence, with variation observed between life stages and body parts. Fluorescence was documented in 88% of hydromedusae (Leptothecata, Anthoathecata, Limnomedusae and Narcomedusae), 50% of hydroid, and 75% of siphonophore taxa that were observed in this study. Our results illustrate how fluorescence patterns may serve as a useful diagnostic tool to explore marine biodiversity, highlighting the need for further documentation of fluorescence patterns across marine diversity and research into the molecules that underlie this phenomenon.

Omnipresent gravity affects all living organisms; it was a vital factor in the past and the current bottleneck for future space exploration. However, little is known about the evolution of gravity sensing and the comparative biology of gravity reception. Here, by tracing the parallel evolution of gravity sensing, we encounter situations when assemblies of homologous modules result in the emergence of non-homologous structures with similar systemic properties. This is a perfect example to study homoplasy at all levels of biological organization. Apart from numerous practical implementations for bioengineering and astrobiology, the diversity of gravity signaling presents unique reference paradigms to understand hierarchical homology transitions to the convergent evolution of integrative systems. Second, by comparing gravisensory systems in major superclades of basal metazoans (ctenophores, sponges, placozoans, cnidarians, and bilaterians), we illuminate parallel evolution and alternative solutions implemented by basal metazoans toward spatial orientation, focusing on gravitational sensitivity and locomotory integrative systems.

Abstract Background Opsins are the primary proteins responsible for light detection in animals. Cnidarians (jellyfish, sea anemones, corals) have diverse visual systems that have evolved in parallel with bilaterians (squid, flies, fish) for hundreds of millions of years. Medusozoans (e.g., jellyfish, hydroids) have evolved eyes multiple times, each time independently incorporating distinct opsin orthologs. Anthozoans (e.g., corals, sea anemones,) have diverse light-mediated behaviors and, despite being eyeless, exhibit more extensive opsin duplications than medusozoans. To better understand the evolution of photosensitivity in animals without eyes, we increased anthozoan representation in the phylogeny of animal opsins and investigated the large but poorly characterized opsin family in the sea anemone Nematostella vectensis. Results We analyzed genomic and transcriptomic data from 16 species of cnidarians to generate a large opsin phylogeny (708 sequences) with the largest sampling of anthozoan sequences to date. We identified 29 opsins from N. vectensis (NvOpsins) with high confidence, using transcriptomic and genomic datasets. We found that lineage-specific opsin duplications are common across Cnidaria, with anthozoan lineages exhibiting among the highest numbers of opsins in animals. To establish putative photosensory function of NvOpsins, we identified canonically conserved protein domains and amino acid sequences essential for opsin function in other animal species. We show high sequence diversity among NvOpsins at sites important for photoreception and transduction, suggesting potentially diverse functions. We further examined the spatiotemporal expression of NvOpsins and found both dynamic expression of opsins during embryonic development and sexually dimorphic opsin expression in adults. Conclusions These data show that lineage-specific duplication and divergence has led to expansive diversity of opsins in eyeless cnidarians, suggesting opsins from these animals may exhibit novel biochemical functions. The variable expression patterns of opsins in N. vectensis suggest opsin gene duplications allowed for a radiation of unique sensory cell types with tissue- and stage-specific functions. This diffuse network of distinct sensory cell types could be an adaptive solution for varied sensory tasks experienced in distinct life history stages in Anthozoans.

DNA methylation, an important component of eukaryotic epigenetics, varies in pattern and function across Metazoa. Notably, bilaterian vertebrates and invertebrates differ dramatically in gene body methylation (GbM). Using the frequency of cytosine-phospho-guanines (CpGs), which are lost through mutation when methylated, we report the first broad survey of DNA methylation in Cnidaria, the ancient sister group to Bilateria. We find that: 1) GbM differentially relates to expression categories as it does in most bilaterian invertebrates, but distributions of GbM are less discretely bimodal. 2) Cnidarians generally have lower CpG frequencies on gene bodies than bilaterian invertebrates potentially suggesting a compensatory mechanism to replace CpG lost to mutation in Bilateria that is lacking in Cnidaria. 3) GbM patterns show some consistency within taxonomic groups such as the Scleractinian corals; however, GbM patterns variation across a range of taxonomic ranks in Cnidaria suggests active evolutionary change in GbM within Cnidaria. 4) Some but not all GbM variation is associated with life history change and genome expansion, whereas GbM loss is evident in endoparasitic cnidarians. 5) Cnidarian repetitive elements are less methylated than gene bodies, and methylation of both correlate with genome repeat content. 6) These observations reinforce claims that GbM evolved in stem Metazoa. Thus, this work supports overlap between DNA methylation processes in Cnidaria and Bilateria, provides a framework to compare methylation within and between Cnidaria and Bilateria, and demonstrates the previously unknown rapid evolution of cnidarian methylation.

The Ediacaran of eastern Newfoundland preserves the world’s oldest known eumetazoan body fossils, as well as the earliest known record of fossilized muscular tissue. Re-examination of the holotype of the eight-armed Haootia quadriformis in terms of its morphology, the arrangement of its muscle filament bundles, and hitherto undescribed aspects of its anatomy support its interpretation as a crown staurozoan. We also document several new fossils preserving muscle tissue with a different muscular architecture to Haootia, but with only four arms. This new material allows us to describe a new crown group staurozoan, Mamsetia manunis gen. et sp. nov. This work confirms the presence of crown group medusozoan cnidarians of the Staurozoa in the Ediacaran of Newfoundland circa 565 Ma.

Owing to global climate change or the ever-more frequent human activities in the offshore areas, it is highly probable that an imbalance in the offshore ecosystem has been induced. However, the importance of maintaining and protecting marine ecosystems’ balance cannot be overstated. In recent years, various marine disasters have occurred frequently, such as harmful algal blooms (green tides and red tides), storm surge disasters, wave disasters, sea ice disasters, and tsunami disasters. Additionally, overpopulation of certain marine organisms (particularly marine faunas) has led to marine disasters, threatening both marine ecosystems and human safety. The marine ecological disaster monitoring system in China primarily focuses on monitoring and controlling the outbreak of green tides (mainly caused by outbreaks of some Ulva species) and red tides (mainly caused by outbreaks of some diatom and dinoflagellate species). Currently, there are outbreaks of Cnidaria (Hydrozoa and Scyphozoa organisms; outbreak species are frequently referred to as jellyfish), Annelida (Urechis unicinctus Drasche, 1880), Mollusca (Philine kinglipini S. Tchang, 1934), Arthropoda (Acetes chinensis Hansen, 1919), and Echinodermata (Asteroidea organisms, Ophiuroidea organisms, and Acaudina molpadioides Semper, 1867) in China. They not only cause significant damage to marine fisheries, tourism, coastal industries, and ship navigation but also have profound impacts on marine ecosystems, especially near nuclear power plants, sea bathing beaches, and infrastructures, posing threats to human lives. Therefore, this review provides a detailed introduction to the marine organisms (especially marine fauna species) causing marine biological disasters in China, the current outbreak situations, and the biological backgrounds of these outbreaks. This review also provides an analysis of the causes of these outbreaks. Furthermore, it presents future prospects for marine biological disasters, proposing corresponding measures and advocating for enhanced resource utilization and fundamental research. It is recommended that future efforts focus on improving the monitoring of marine biological disasters and integrating them into the marine ecological disaster monitoring system. The aim of this review is to offer reference information and constructive suggestions for enhancing future monitoring, early warning systems, and prevention efforts related to marine ecological disasters in support of the healthy development and stable operation of marine ecosystems.

Current sampling methods for detecting the presence of the invasive freshwater hydrozoan Craspedacusta sowerbii rely mainly on visual confirmation of the medusa stage. Confirming the presence of the polyp stage is equally important for observing medusae since typical late summer/early fall occurrences or observations of medusae are sporadic though are becoming more frequent. The polyp stage is important as it is the organism’s primary stage and is present throughout the year depending on water temperatures. Therefore, sampling methods for the polyp stage are, commonly, the collection of substrates such as rocks, plants, or pieces of wood in a given body of water, and these can be cumbersome to examine. Polyps are also small, transparent, and difficult to see on natural substrates. Based on a preliminary culturing of the polyp stage on glass and plastic microscope slides in the laboratory, we designed a sampling methodology based on submerging four substrate types (glass and plastic microscope slides, Hester-Dendy discs, and small glass Petri dishes) to confirm the presence of C. sowerbii polyps in the field. We tested this method in three lakes in the Illinois–Indiana region (USA). Two of the lakes have recorded sightings of medusae but the third has no record of polyps or medusae. The sampling method we designed was effective in that C. sowerbii polyps were found on both plastic and glass slides. While this method can be sufficient for detection of the polyp stage, it also shows potential for improvement; we highlight abiotic and biotic ecological parameters as significant factors influencing the collection of C. sowerbii polyps to be considered for future methodologies.

Porpita porpita is a colonial polymorphic hydrozoan distributed in temperate and tropical zones. This species, like most hydrozoans, possesses a metagenetic life cycle with alternating life forms: medusa stage, polypoid colony, and planula larva. However, a characterization of its early stages of development is still lacking. For this study, an integrative description of the larval stages and the hydroid colony was performed using molecular and histologic tools. The results show that P. porpita develops through three larval stages: preplanula, planula, and premetamorphic planula. The preplanula is distinguished by an absence of polarity, the planula by differentiation of the oral–aboral poles, and the premetamorphic stage by cellular differentiation. Furthermore, two morphologies of young hydroids with different developmental patterns of gonozooids and dactylozooids were observed; notably, it was not possible to observe the gastrozooid in either. Taxonomic identification was confirmed using mitochondrial (COI) and ribosomal (18S and 28S) markers. Our analysis indicates that the COI gene exhibits higher intraspecific variability compared to the 18s and 28s rDNA ribosomal genes. The presented results support the future identification of P. porpita based on morphological characteristics, regardless of the stage of development. Specifically, they shed light on the diversity of mesozooplankton in reef communities.

Jellyfish are aquatic animals of the phylum Cnidaria found in seas all over the world. They are characterized by the presence of cnidocytes, cells that contain a secretory organelle, the cnidocyst, mainly used for predation and defense purposes. An adult female patient presented to our Unit of Dermatology, for a 10 days-old history of macular-erythematous lesions in her right upper limb, due to a sting by a mauve stinger Pelagia noctiluca. Dermoscopy showed a general pinkish background surmounted by numerous brown dots and lines, distributed along the surface of the skin. Reflectance confocal microscopy (RCM) showed the presence of multiple partially hyperreflective, highly coiled, hollow, and harpoonlike structures through the epidermis but without the barbed tubes found in a previous RCM report, likely due to a greater time elapsed between the sting and the dermatological visit. This case highlights how dermoscopy and RCM may help clinicians for the diagnosis of jellyfish stings.

BMP signaling has a conserved function in patterning the dorsal-ventral body axis in Bilateria and the directive axis in anthozoan cnidarians. So far, cnidarian studies have focused on the role of different BMP signaling network components in regulating pSMAD1/5 gradient formation. Much less is known about the target genes downstream of BMP signaling. To address this, we generated a genome-wide list of direct pSMAD1/5 target genes in the anthozoan Nematostella vectensis, several of which were conserved in Drosophila and Xenopus. Our ChIP-seq analysis revealed that many of the regulatory molecules with documented bilaterally symmetric expression in Nematostella are directly controlled by BMP signaling. We identified several so far uncharacterized BMP-dependent transcription factors and signaling molecules, whose bilaterally symmetric expression may be indicative of their involvement in secondary axis patterning. One of these molecules is zswim4-6, which encodes a novel nuclear protein that can modulate the pSMAD1/5 gradient and potentially promote BMP-dependent gene repression.

The scyphozoan Cassiopea xamachana is an emerging cnidarian model system for studying regeneration, animal-algae symbiotic relationships, and various aspects of evolutionary biology including the early emergence of animal nervous systems. Cassiopea has a life cycle similar to other scyphozoans, which includes the alternation between a sessile, asexual form (polyp) and a sexually reproducing stage, the medusa. The transition between the two forms is called strobilation, where the polyp releases a miniature medusa, the iconic ephyra, that subsequently develops into the adult medusa. In addition, Cassiopea polyps may reproduce asexually by budding off free-swimming so-called planuloid buds. While the development of planuloid buds and polyps has been studied in some detail, little is known about the ontogeny of the sexually produced planula larva. Using immunofluorescence labeling and confocal microscopy, we examined neuromuscular development during metamorphosis of the planula larva into the juvenile polyp in C. xamachana. For this purpose, we used tyrosinated α-tubulin-, FMRFamide- and serotonin-like immunoreactivity together with phalloidin labeling. Our results show a planula nervous system that consists of a basiectodermal neural plexus with mostly longitudinally oriented neurites. This neural meshwork is connected to sensory neurons in the superficial stratum of the ectoderm, which are exclusively localized in the aboral half of the larva. During settlement, this aborally concentrated nervous system of the planula is replaced completely by the orally concentrated nervous system of the polyp. Adult polyps show an extensive nerve net with a loose concentration around the oral disc. These findings are consistent with data from other scyphozoans and most likely constitute a conserved feature of scyphozoan discomedusae. Taken together, the data currently available suggest an aborally concentrated nervous system including sensory cells as part of the neural ground pattern of cnidarian planula larvae. The reorganization of the nervous system from anterior to posterior in planula-to-polyp metamorphosis most likely also constitutes an ancestral trait in cnidarian evolution.

IntroductionHost-parasite associations provide very useful models to study adaptive processes. We investigated the interaction between carnivorous marine gastropods, the Ovulidae or egg-cowries, and their cnidarian food targets. Ovulidae (Fleming, 1828), is a family of specialized carnivorous caenogastropods that feed by browsing on octocorals (Anthozoa: Octocorallia: Malacalcyonacea and Scleralcyonacea) or, to a much lesser degree, on antipatharians (Anthozoa: Hexacorallia: Antipatharia) and Stylasteridae (Hydrozoa: Hydroidolina: Anthoathecata). Very scanty information is available on the phylogenetic relationships and the degree of specificity of the relationship with the cnidarians of this corallivorous lineage, especially for deep-water taxa.MethodsTo assess taxonomic identifications and investigate cnidarian/ovulid relationships in the context of their evolution, we generated an extensive molecular dataset comprising two mitochondrial (cox1 and 16S rDNA) and one nuclear gene (28S rDNA) from 524 specimens collected worldwide. The coral hosts of the ovulid species have been identified by integrating literature data with new records, employing morphological and/or molecular (the mitochondrial 16S rDNA and mtMSH, and the nuclear ITS2) markers.ResultsWe obtained a molecular phylogenetic framework for the Ovulidae, time-calibrated with nine reliable fossil records. An ancestral state reconstruction allowed to identify Hexacorallia or Hydroidolina as the most likely ancestral cnidarian host for the Ovulidae.DiscussionOur phylogenetic hypothesis revealed the existence of groups that do not completely correspond to the currently employed subfamilial arrangement. Concerning trophic ecology, while only pediculariines (Pedicularia and allied) are associated with hydrozoans (Stylasteridae), our results suggest that some ovulid lineages shifted independently between octocorals and hexacorals.

Planktonic lifestyle of polyps in representatives of Margelopsidae are very different from all other species in the hydrozoan clade Aplanulata. Their evolutionary origin and phylogenetic position have been the subject of significant speculation. A recent molecular study based only on COI data placed Margelopsidae as a sister group to all Aplanulata, an unexpected result because margelopsid morphology suggests affiliation with Tubulariidae or Corymorphidae. Here we used multigene analyses, including nuclear (18S rRNA and 28S rRNA) and mitochondrial (16S rRNA and COI) markers of the hydroid stage of the margelopsid species Margelopsis haeckelii and the medusa stage of Margelopsis hartlaubii to resolve their phylogenetic position with respect to other hydrozoans. Our data provide strong evidence that M. haeckelii, the type species of Margelopsis, is a member of the family Corymorphidae. In contrast, M. hartlaubii is sister to Plotocnide borealis, a member of Boreohydridae. These results call into question the validity of the genus Margelopsis and the family Margelopsidae. The systematic position of M. haeckelii is discussed in light of the phylogeny of Corymorphidae.

In bilaterian central nervous systems, coordination of neurotransmission by glial cells enables highly sophisticated neural functions. The diversity of transcription factors (TFs) involved in gliogenesis suggests multiple evolutionary origins of various glial cell types of bilaterians. Many of these TFs including the glial cells missing (Gcm) are also present in genomes of Cnidaria, the closest outgroup to Bilateria, but their function remains to be elucidated. In this study, we analyzed the function of Gcm, a multifunctional TF involved in development of glial and non-glial cell types, in the sea anemone, Nematostella vectensis. siRNA-mediated knockdown of Nematostella Gcm altered expression of cell adhesion proteins, glutamate and GABA transporters, ion channels, metabolic enzymes, and zinc finger and Ets-related TFs. NvGcm and mRNAs of downstream genes are expressed in broad neural cell clusters. However, immunostaining of a NvGcm target protein, the glutamate transporter, NvEAAT1, visualized a novel class of cells with flat cell bodies and no clear processes. Together with the finding of unique morphological features of NvEAAT1-functioning cells, these data suggest that extracellular glutamate metabolism, one of major glial functions, is deployed downstream of Gcm in specific neural cell types in Cnidaria. [ABSTRACT FROM AUTHOR]

Photosymbiotic cnidarians generally seek bright environments so that their symbionts can be photosynthetically active. However, excess light may result in a breakdown of symbiosis due to the accumulation of photodamage in symbionts causing symbiont loss (bleaching). It is currently unknown if photosymbiotic cnidarians sense light only to regulate spawning time and to facilitate predation, or whether they also use their light-sensing capacities to protect their symbionts from photodamage. In this study, we examined how the sea anemone Aiptasia changes its behaviour when exposed to excess light. We reveal that Aiptasia polyps, when carrying symbionts, contract their bodies when exposed to high light intensities and subsequently migrate away in a direction perpendicular to the light source. Interestingly, this negative phototaxis was only evident under blue light and absent upon UV, green and red light exposure. Non-symbiotic Aiptasia did not exhibit this light response. Our study demonstrates that photosymbiotic Aiptasia polyps display negative phototactic behaviour in response to blue light, and that they also can perceive its direction, despite lacking specialized eye structures. We postulate that Aiptasia uses blue light, which penetrates seawater efficiently, as a general proxy for sunlight exposure to protect its symbionts from photodamage. [ABSTRACT FROM AUTHOR]

The emergence of previously unknown disease-causing viruses in mammals is in part the result of a long-term evolutionary process. Reconstructing the deep phylogenetic histories of viruses helps identify major evolutionary transitions and contextualizes the emergence of viruses in new hosts. We used a combination of total RNA sequencing and transcriptome data mining to extend the diversity and evolutionary history of the RNA virus order Articulavirales, which includes the influenza viruses. We identified instances of Articulavirales in the invertebrate phylum Cnidaria (including corals), constituting a novel and divergent family that we provisionally named the "Cnidenomoviridae." We further extended the evolutionary history of the influenza virus lineage by identifying four divergent, fish-associated influenza-like viruses, thereby supporting the hypothesis that fish were among the first hosts of influenza viruses. In addition, we substantially expanded the phylogenetic diversity of quaranjaviruses and proposed that this genus be reclassified as a family--the "Quaranjaviridae." Within this putative family, we identified a novel arachnid-infecting genus, provisionally named "Cheliceravirus." Notably, we observed a close phylogenetic relationship between the Crustacea-and Chelicerata-infecting "Quaranjaviridae" that is inconsistent with virus-host codivergence. Together, these data suggest that the Articulavirales has evolved over at least 600 million years, first emerging in aquatic animals. Importantly, the evolution of the Articulavirales was likely shaped by multiple aquatic-terrestrial transitions and substantial host jumps, some of which are still observable today. [ABSTRACT FROM AUTHOR]

Epithelial wound healing involves the collective responses of many cells, including those at the wound margin (marginal cells) and those that lack direct contact with the wound (submarginal cells). How these responses are induced and coordinated to produce rapid, efficient wound healing remains poorly understood. Extracellular ATP (eATP) is implicated as a signal in epithelial wound healing in vertebrates. However, the role of eATP in wound healing in vivo and the cellular responses to eATP are unclear. Almost nothing is known about eATP signaling in non-bilaterian metazoans (Cnidaria, Ctenophora, Placozoa, and Porifera). Here, we show that eATP promotes closure of epithelial wounds in vivo in the cnidarian Clytia hemisphaerica (Clytia) indicating that eATP signaling is an evolutionarily ancient strategy in wound healing. Furthermore, eATP increases F-actin accumulation at the edges of submarginal cells. In Clytia, this indicates eATP is involved in coordinating cellular responses during wound healing, acting in part by promoting actin remodeling in cells at a distance from the wound. We also present evidence that eATP activates a cation channel in Clytia epithelial cells. This implies that the eATP signal is transduced through a P2X receptor (P2XR). Phylogenetic analyses identified four Clytia P2XR homologs and revealed two deeply divergent major branches in P2XR evolution, necessitating revision of current models. Interestingly, simple organisms such as cellular slime mold appear exclusively on one branch, bilaterians are found exclusively on the other, and many non-bilaterian metazoans, including Clytia, have P2XR sequences from both branches. Together, these results re-draw the P2XR evolutionary tree, provide new insights into the origin of eATP signaling in wound healing, and demonstrate that the cytoskeleton of submarginal cells is a target of eATP signaling. [ABSTRACT FROM AUTHOR]

Neurons underpin cognition in animals. However, the roots of animal cognition are elusive from both mechanistic and evolutionary standpoints. Two conceptual frameworks both highlight and promise to address these challenges. First, we discuss evidence that animal neural and other integrative systems evolved more than once (convergent evolution) within basal metazoan lineages, giving us unique experiments by Nature for future studies. The most remarkable examples are neural systems in ctenophores and neuroid-like systems in placozoans and sponges. Second, in addition to classical synaptic wiring, a chemical connectome mediated by hundreds of signal molecules operates in tandem with neurons and is the most information-rich source of emerging properties and adaptability. The major gap—dynamic, multifunctional chemical micro-environments in nervous systems—is not understood well. Thus, novel tools and information are needed to establish mechanistic links between orchestrated, yet cell-specific, volume transmission and behaviors. Uniting what we call chemoconnectomics and analyses of the cellular bases of behavior in basal metazoan lineages arguably would form the foundation for deciphering the origins and early evolution of elementary cognition and intelligence. [ABSTRACT FROM AUTHOR]

This research provides an extensive analysis of the biodiversity and distribution patterns of copepod crustaceans associated with octocoral species. A comprehensive dataset comprising 966 records pertaining to 233 copepod species, encompassing 54 genera, 18 families, and 3 orders, was compiled from 92 scientific papers published between 1858 and 2023, and updated as open data to GBIF. These copepods were found to be closely associated with 183 octocoral species, representing 72 genera and 28 families. The analysis revealed a total of 393 distinct interspecific associations between copepods, classified under the orders Cyclopoida, Harpacticoida, and Siphonostomatoida, and diverse octocorals. Approximately 60% of these associations were reported only once in the literature, which poses challenges to assessing the level of host specificity among the majority of copepod species linked with octocorals. Notably, over 91% of the recorded copepod species were found at depths not exceeding 30 m, with only four copepod species reported at greater depths surpassing 500 m. The presence of these symbiotic copepods was documented across 215 sampling sites situated within 8 of the 12 defined marine ecoregions, with particular attention to the Western Indo-Pacific, Central Indo-Pacific, and Temperate Northern regions. Despite the comprehensive examination of available data, this study highlights substantial gaps in our comprehension of copepod crustacean diversity and distribution in association with octocorals. Moreover, crucial information concerning symbiotic copepods is conspicuously absent for approximately 94% of potential octocoral host species. These disparities emphasize the imperative need for further scientific inquiry to unveil the intricacies of symbiotic relationships and to contribute to a more holistic understanding of copepod–octocoral associations. [ABSTRACT FROM AUTHOR]

Fish eggs have a wide range of predators. However, observing these predators is challenging, as is identifying fish eggs based on morphological traits. In this study, we observed hydroids, which are sessile organisms, consuming pelagic fish eggs. We conducted cytochrome c oxidase I (COI) metabarcoding to identify both the predator and the prey species. Massive COI reads were de novo assembled and nine representative sequences were constructed. The predator, identified from the representative sequences and its morphological features, was determined as Ectopleura crocea. The fish eggs that had been preyed upon belonged to two species: Sillago japonica and Parajulis poecilepterus. Additionally, four arthropod species (Labidocera rotunda, Oithona similis, Paracalanus parvus, and Pseudevadne tergestina) were consumed, and their morphological traits could not be observed, due to digestion. COI metabarcoding was an effective tool for studying the feeding activity of these small predators. [ABSTRACT FROM AUTHOR]

Efficient nutrient recycling underpins the ecological success of cnidarian-algal symbioses in oligotrophic waters. In these symbioses, nitrogen limitation restricts the growth of algal endosymbionts in hospite and stimulates their release of photosynthates to the cnidarian host. However, the mechanisms controlling nitrogen availability and their role in symbiosis regulation remain poorly understood. Here, we studied the metabolic regulation of symbiotic nitrogen cycling in the sea anemone Aiptasia by experimentally altering labile carbon availability in a series of experiments. Combining 13C and 15N stable isotope labeling experiments with physiological analyses and NanoSIMS imaging, we show that the competition for environmental ammonium between the host and its algal symbionts is regulated by labile carbon availability. Light regimes optimal for algal photosynthesis increase carbon availability in the holobiont and stimulate nitrogen assimilation in the host metabolism. Consequently, algal symbiont densities are lowest under optimal environmental conditions and increase toward the lower and upper light tolerance limits of the symbiosis. This metabolic regulation promotes efficient carbon recycling in a stable symbiosis across a wide range of environmental conditions. Yet, the dependence on resource competition may favor parasitic interactions, explaining the instability of the cnidarian-algal symbiosis as environmental conditions in the Anthropocene shift towards its tolerance limits. Photosymbioses enable efficient nutrient recycling between heterotrophic and phototrophic organisms. This study shows that nutrient cycling in a cnidarian-algal symbiosis is regulated through resource competition between symbiotic partners. Mutualistic interactions can therefore emerge from mutual exploitation in nutrient–exchange symbioses. [ABSTRACT FROM AUTHOR]

Amplicon capture is a promising target sequence capture approach for phylogenomic analyses, and the design of clade-specific nuclear protein-coding locus (NPCL) amplification primers is crucial for its successful application. In this study, we developed a primer design program called UPrimer that can quickly design clade-specific NPCL amplification primers based on genome data, without requiring manual intervention. Unlike other available primer design programs, UPrimer uses a nested-PCR strategy that greatly improves the amplification success rate of the designed primers. We examined all available metazoan genome data deposited in NCBI and developed NPCL primer sets for 21 metazoan groups with UPrimer, covering a wide range of taxa, including arthropods, mollusks, cnidarians, echinoderms, and vertebrates. On average, each clade-specific NPCL primer set comprises ∼1,000 NPCLs. PCR amplification tests were performed in 6 metazoan groups, and the developed primers showed a PCR success rate exceeding 95%. Furthermore, we demonstrated a phylogenetic case study in Lepidoptera, showing how NPCL primers can be used for phylogenomic analyses with amplicon capture. Our results indicated that using 100 NPCL probes recovered robust high-level phylogenetic relationships among butterflies, highlighting the utility of the newly designed NPCL primer sets for phylogenetic studies. We anticipate that the automated tool UPrimer and the developed NPCL primer sets for 21 metazoan groups will enable researchers to obtain phylogenomic data more efficiently and cost-effectively and accelerate the resolution of various parts of the Tree of Life. [ABSTRACT FROM AUTHOR]

Background: Diadumene lineata is one of the most widespread sea anemone species worldwide. Although this species has been reported a few times on the Argentine coast since 2004, its identification has traditionally been based on external morphological characteristics, and in most cases no voucher specimens are available to support previous records. Methods: In this study, we obtained DNA sequences of two mitochondrial markers (12S and 16S) and two nuclear markers (18S and 28S) from specimens of D. lineata collected in two locations on the Argentine coast separated by almost 800 km. Additionally, we conducted an analysis of the morphology, as well as the types and size ranges of cnidae, using specimens collected at three different locations along the Argentine coast. Furthermore, since introduced populations of D. lineata are presumably ephemeral and only reproduce asexually outside their native range, we examined the internal anatomy of representatives from the Argentine coast for gametogenic tissue as an indication of whether they might be capable of sexual reproduction. Results: DNA data support our morphological identification, including cnidae analyses, of the specimens as D. lineata. Furthermore, all specimens examined were determined to be sterile. Discussion: Genetic sequence comparisons, phylogenetic reconstruction, and cnidae data support the identification of individuals of D. lineata from Mar Chiquita and Garipe Beach, confirming the presence of the species on the Argentine coast using both morphological and molecular tools. The absence of fertile specimens suggests that each sampled population is likely reproducing only by asexual reproduction and possibly composed of clones. The presence of an additional category of longer pmastigophores B2a in the actinopharynx and filaments, as well as holotrichs in the column, is also reported. Conclusions: For the first time, we have confirmed the presence of D. lineata in Argentina through molecular data. Additionally, our findings indicate that the analyzed specimens are sterile, suggesting that this species is not engaging in sexual reproduction in the studied localities. It is crucial to continue monitoring the populations of D. lineata along the Argentine coast to assess whether they establish sexual reproduction, expand their distribution range or disappear, or potentially cause any harm to local species or alterations in benthic communities. [ABSTRACT FROM AUTHOR]

This study determined the complete mitochondrial genome of the jellyfish Pelagia noctiluca (Scyphozoa, Semaeostomeae) for the first time. The genome was a linear molecule of 16,390 bp in length and 59.3% AT. It comprised of 13 typical protein-coding genes (cox1-3, nd1-6, nd4L, atp6, atp8, and cytB), two ribosomal RNAs (16S and 12S rRNA), and two tRNAs (trnM and trnW). In addition, we detected two additional open reading frames (polB and ORF314) at one end of the genome. The genecoding structures were identical to those of other scyphozoans. Based on a molecular phylogeny constructed using 13 protein-coding genes, P. noctiluca has the closest genetic relationship with the genus Chrysaora (Semaeostomeae). [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]

The foxn4 is one of the key transcription factor genes controlling retinal formation in vertebrates. However, it is not clear whether its association with light-sensitive organ formation is evolutionary conserved. To answer this question, the authors tested whether the expression of this gene is localized within light-sensitive organs in a representative of basal Metazoa, the hydroid Sarsia lovenii (Hydrozoa, Cnidaria). Usually, the life cycle of hydroids includes stages of a pelagic medusa and a benthic polyp. However, in many species, attached medusoids, in which many medusal structures are reduced, form instead of free-swimming medusaе. The White Sea hydrozoan Sarsia lovenii is an exceptional example of the species, in which polyps of different haplotypes produce either pelagic medusae or attached medusoids. Comparison of gene expression in medusae and medusoids of S. lovenii is a promising model to study how the formation of morphological traits is regulated in hydrozoan cnidarians. We compared the spatial pattern of foxn4 expression in medusae and medusoids of S. lovenii by in situ hybridization. In medusae, foxn4 is expressed not in the photoreceptive ocelli but in the ectoderm of the tentacle bulb around the ocellus. Although, unlike medusae, S. lovenii medusoids lack ocelli, we detected foxn4 expression in their reduced tentacle bulbs. It is known that the tentacle bulb in hydrozoan medusae is a zone of localized formation of nematocytes, which are considered to be derivatives of mechanosensory cells. Thus, our results indicate that, in medusae and medusoids of S. lovenii, the foxn4 is not associated with the formation of light-sensitive organs, as in vertebrates. However, it may be associated with nematocytes, another type of neurosensory cells. [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]

This paper describes the study of a small collection of Sertularioidea Lamouroux, 1812 (Cnidaria, Hydrozoa) collected along the Guinea Current Large Marine Ecosystem (GCLME) during four oceanographic surveys performed between 2005 and 2008. The samples were collected at 12 stations located at depths between 18 and 359 m using a bottom trawl and a Petersen grab. A total of 112 colonies were identified, belonging to 13 species, nine genera, and three families. The family Sertulariidae showed the highest species richness, with 11 species, whereas the families Thyroscyphidae and Sertularellidae were represented only by one species each. In this manuscript is described the first report of Salacia tetracythara in the Eastern Atlantic, Abietinaria abietina in West Africa, and Salacia desmoides in the GCLME region. One species was only described to the genus level, and material of Dynamena dalmasi from Cape Verde was also examined as comparison material. [ABSTRACT FROM AUTHOR]

Diabetes mellitus is one of the most serious diseases of our century. The drugs used are limited or have serious side effects. The search for new sources of compounds for effective treatment is relevant. Magnificamide, a peptide inhibitor of mammalian α-amylases, isolated from the venom of sea anemone Heteractis magnifica, can be used for the control of postprandial hyperglycemia in diabetes mellitus. Using the RACE approach, seven isoforms of magnificamide were detected in H. magnifica tentacles. The exon–intron structure of magnificamide genes was first established, and intron retention in the mature peptide-encoding region was revealed. Additionally, an α-amylase inhibitory domain was discovered in the mucins of some sea anemones. According to phylogenetics, sea anemones diverge into two groups depending on the presence of β-defensin-like α-amylase inhibitors and/or mucin-inhibitory domains. It is assumed that the intron retention phenomenon leads to additional diversity in the isoforms of inhibitors and allows for its neofunctionalization in sea anemone tentacles. Bioprospecting of sea anemones of the order Actiniaria for β-defensin-like α-amylase inhibitors revealed a diversity of inhibitory sequences that represents a starting point for the design of effective glucose-lowering drugs. [ABSTRACT FROM AUTHOR]

Across eukaryotes, large variations of genome sizes have been observed even between closely related species. Transposable elements as part of the repeated DNA have been proposed and confirmed as one of the most important contributors to genome size variation. However, the evolutionary implications of genome size variation and transposable element dynamics are not well understood. Together with phenotypic traits, they are commonly referred to as the "C-value enigma''. The order Zoantharia are benthic cnidarians found from intertidal zones to the deep sea, and some species are particularly abundant in coral reefs. Despite their high ecological relevance, zoantharians have yet to be largely studied from the genomic point of view. This study aims at investigating the role of the repeatome (total content of repeated elements) in genome size variations across the order Zoantharia. To this end, whole-genomes of 32 zoantharian species representing five families were sequenced. Genome sizes were estimated and the abundances of different repeat classes were assessed. In addition, the repeat overlap between species was assessed by a sequence clustering method. The genome sizes in the dataset varied up to 2.4 fold magnitude. Significant correlations between genome size, repeated DNA content and transposable elements, respectively (Pearson's correlation test R² = 0:47, p = 0.0016; R² = 0:22, p = 0.05) were found, suggesting their involvement in the dynamics of genome expansion and reduction. In all species, long interspersed nuclear elements and DNA transposons were the most abundant identified elements. These transposable elements also appeared to have had a recent expansion event. This was in contrast to the comparative clustering analysis which revealed species-specific patterns of satellite elements' amplification. In summary, the genome sizes of zoantharians likely result from the complex dynamics of repeated elements. Finally, the majority of repeated elements (up to 70%) could not be annotated to a known repeat class, highlighting the need to further investigate non-model cnidarian genomes. More research is needed to understand how repeated DNA dynamics relate to zoantharian evolution and their biology. [ABSTRACT FROM AUTHOR]

The mitogenome of a soft coral, Eleutherobia rubra (Brundin, 1896), was completely sequenced for the first time. The total mitogenome length of E. rubra is 18,724 bp with 14 protein-coding genes, two ribosomal RNA genes, one transfer RNA gene (tRNA–Met), and one non-coding region (NCR). The gene order is also consistent with other Alcyoniidae species. The base composition is 30.1% A, 16.7% C, 19.5% G, and 33.7% T, with a G–C content of 36.2%. This is the first record of the complete mitogenome sequence of the genus Eleutherobia. [ABSTRACT FROM AUTHOR]

The jellyfish Cassiopea largely cover their carbon demand via photosynthates produced by microalgal endosymbionts, but how holobiont morphology and tissue optical properties affect the light microclimate and symbiont photosynthesis in Cassiopea remain unexplored. Here, we use optical coherence tomography (OCT) to study the morphology of Cassiopea medusae at high spatial resolution. We include detailed 3D reconstructions of external micromorphology, and show the spatial distribution of endosymbionts and white granules in the bell tissue. Furthermore, we use OCT data to extract inherent optical properties from light-scattering white granules in Cassiopea, and show that granules enhance local light-availability for symbionts in close proximity. Individual granules had a scattering coefficient of µs = 200–300 cm−1, and scattering anisotropy factor of g = 0.7, while large tissue-regions filled with white granules had a lower µs = 40–100 cm−1, and g = 0.8–0.9. We combined OCT information with isotopic labelling experiments to investigate the effect of enhanced light-availability in whitish tissue regions. Endosymbionts located in whitish tissue exhibited significantly higher carbon fixation compared to symbionts in anastomosing tissue (i.e. tissue without light-scattering white granules). Our findings support previous suggestions that white granules in Cassiopea play an important role in the host modulation of the light-microenvironment. [ABSTRACT FROM AUTHOR]

Background: As the sister group to all Bilateria, representatives of the phylum Cnidaria (sea anemones, corals, jellyfishes, and hydroids) possess a recognizable and well-developed nervous system and have attracted considerable attention over the years from neurobiologists and evo-devo researchers. Despite a long history of nervous system investigation in Cnidaria, most studies have been performed on unitary organisms. However, the majority of cnidarians are colonial (modular) organisms with unique and specific features of development and function. Nevertheless, data on the nervous system in colonial cnidarians are scarce. Within hydrozoans (Hydrozoa and Cnidaria), a structurally "simple" nervous system has been described for Hydra and zooids of several colonial species. A more complex organization of the nervous system, closely related to the animals' motile mode of life, has been shown for the medusa stage and a few siphonophores. Direct evidence of a colonial nervous system interconnecting zooids of a hydrozoan colony has been obtained only for two species, while it has been stated that in other studied species, the coenosarc lacks nerves. Methods: In the present study, the presence of a nervous system in the coenosarc of three species of colonial hydroids - the athecate Clava multicornis, and thecate Dynamena pumila and Obelia longissima - was studied based on immunocytochemical and ultrastructural investigations. Results: Confocal scanning laser microscopy revealed a loose system composed of delicate, mostly bipolar, neurons visualized using a combination of anti-tyrosinated and anti-acetylated a-tubulin antibodies, as well as anti-RF-amide antibodies. Only ganglion nerve cells were observed. The neurites were found in the growing stolon tips close to the tip apex. Ultrastructural data confirmed the presence of neurons in the coenosarc epidermis of all the studied species. In the coenosarc, the neurons and their processes were found to settle on the mesoglea, and the muscle processes were found to overlay the nerve cells. Some of the neurites were found to run within the mesoglea. Discussion: Based on the findings, the possible role of the colonial nervous system in sessile hydroids is discussed. [ABSTRACT FROM AUTHOR]

Background: Opsins are the primary proteins responsible for light detection in animals. Cnidarians (jellyfish, sea anemones, corals) have diverse visual systems that have evolved in parallel with bilaterians (squid, flies, fish) for hundreds of millions of years. Medusozoans (e.g., jellyfish, hydroids) have evolved eyes multiple times, each time independently incorporating distinct opsin orthologs. Anthozoans (e.g., corals, sea anemones,) have diverse light-mediated behaviors and, despite being eyeless, exhibit more extensive opsin duplications than medusozoans. To better understand the evolution of photosensitivity in animals without eyes, we increased anthozoan representation in the phylogeny of animal opsins and investigated the large but poorly characterized opsin family in the sea anemone Nematostella vectensis. Results: We analyzed genomic and transcriptomic data from 16 species of cnidarians to generate a large opsin phylogeny (708 sequences) with the largest sampling of anthozoan sequences to date. We identified 29 opsins from N. vectensis (NvOpsins) with high confidence, using transcriptomic and genomic datasets. We found that lineage-specific opsin duplications are common across Cnidaria, with anthozoan lineages exhibiting among the highest numbers of opsins in animals. To establish putative photosensory function of NvOpsins, we identified canonically conserved protein domains and amino acid sequences essential for opsin function in other animal species. We show high sequence diversity among NvOpsins at sites important for photoreception and transduction, suggesting potentially diverse functions. We further examined the spatiotemporal expression of NvOpsins and found both dynamic expression of opsins during embryonic development and sexually dimorphic opsin expression in adults. Conclusions: These data show that lineage-specific duplication and divergence has led to expansive diversity of opsins in eyeless cnidarians, suggesting opsins from these animals may exhibit novel biochemical functions. The variable expression patterns of opsins in N. vectensis suggest opsin gene duplications allowed for a radiation of unique sensory cell types with tissue- and stage-specific functions. This diffuse network of distinct sensory cell types could be an adaptive solution for varied sensory tasks experienced in distinct life history stages in Anthozoans. [ABSTRACT FROM AUTHOR]