Search

Anthopleura is one of the most speciose genera within the family Actiniidae. This genus is particularly characterized by its members having both verrucae on the column and acrorhagi on the margin. In the region of the Baja California Peninsula, in the Mexican Pacific, six species of Anthopleura have been documented, which are relatively well defined by their morphological characteristics and coloration patterns. During recent visits to the intertidal zone of Cerritos, in Baja California Sur, we found individuals of Anthopleura displaying a variety of colorations that do not agree with known species for the region. We collected and examined specimens of four morphotypes of Anthopleura, analyzing them by integrating information about their external and internal anatomy, as well as their cnidome. Additionally, we obtained and analyzed genetic sequences from mitochondrial and nuclear markers through phylogenetic analyses. Our results reveal that the four morphotypes belong to a single, and undescribed species of Anthopleura. We provide a detailed description of the species Anthopleura variata sp. nov., which is characterized by a variety of coloration patterns, as well as having a circumscribed, palmate, and pedunculate marginal sphincter muscle, harboring zooxanthellae, and lacking directive mesenteries, among other characteristics. Anthopleura variata sp. nov. is the 49th species in the genus and the seventh species of Anthopleura documented for the Mexican Pacific. [ABSTRACT FROM AUTHOR]

Sea anemones are venomous animals that rely on their venom for prey capture, defense against predators, and intraspecific competition. Currently, comprehensive molecular and evolutionary analyses of the toxin repertoire for sea anemones are limited by a lack of proteomic data for most species. In this study, proteo-transcriptomic analysis was used to expand our knowledge of the proteinaceous components of sea anemone venom by determining the secreted venom proteome of Calliactis polypus. Electromechanical stimulation was used to obtain the secreted venom of C. polypus. We identified a low complexity proteome that was dominated by toxins with similarity to known neurotoxins, as well as six novel toxin candidates. The novel putative toxin candidates were found to be taxonomically restricted to species from the superfamily Metridioidea. Furthermore, the secreted venom of C. polypus had only three putative toxins in common with the venom of acontia from the same species and little similarity with the secreted venom of closely related species. Overall, this demonstrates that regionalized and lineage-specific variability in toxin abundance is common among sea anemone species. Moreover, the limited complexity of the toxin repertoire found in C. polypus supports the idea that peptide neurotoxins make up the dominant toxin arsenal found in the venom of sea anemones. [ABSTRACT FROM AUTHOR]

Thermally-induced bleaching events pose significant impacts on coral reefs but current understanding of the bleaching effects on host sea anemones and mutualistic anemonefishes is limited compared to those of scleractinian corals and their associates. Such information is especially lacking in Southeast Asia, despite the region harbouring the highest diversity of host anemones and anemonefishes. In this study, we documented bleaching prevalence and recovery of host anemones and quantified changes in anemonefish abundance at two coral reefs in Singapore during and after the 2016 mass bleaching event. Of the 260 host anemones surveyed, 16% were bleached in July 2016. All Entacmaea quadricolor bleached, in contrast to Heteractis magnifica (1%) and Stichodactyla mertensii (0%). Five months after the warming event, the bleached E. quadricolor had significant size reductions at both sites despite 10% of them regaining pigmentation. In March 2017, recovery rates of E. quadricolor significantly differed between the study sites. Recovered host anemones increased in size while the bleached ones remained the same or continued shrinking. The between-site differences in recovery of bleached E. quadricolor influenced the abundance of associated Amphiprion frenatus, highlighting the importance of bleaching status and associated host anemone size in supporting viable anemonefish populations. Our study represents the first quantitative assessment of anemone bleaching and post-bleaching recovery in Southeast Asia. Considering the increasing frequency and severity of extreme warming events, our findings stress an urgent need to understand climate change impacts on non-scleractinian host organisms and their associates to implement effective management and enhance reef biodiversity conservation. [ABSTRACT FROM AUTHOR]

Metridium senile (Linneaus, 1761) is simultaneously one of the most familiar sea anemones in temperate shallow water and a species embroiled in taxonomic and nomenclatural confusion. Their large body size, characteristic ruff of tentacles, and ability to thrive on artificial and natural substrates make these animals conspicuous and common on rocky ledges, pilings, wharfs, shipwrecks, and bivalve reefs. Their reported range encompasses all temperate habitats in the northern hemisphere plus a handful of locales in the temperate southern hemisphere that have typically been characterized as anthropogenic introductions. Understanding the range of M. senile has been confounded by confusion about its circumscription relative to its congeners and inconsistency in the names used. Here, we summarize the taxonomy of the genus and clarify the status of M. senile. Based on results of recent phylogenetic studies, we consider Metridium to have two valid species: M. farcimen (Brandt, 1835) and M. senile. We recognize M. senile as the valid, appropriate name for all populations of Metridium in the Atlantic and for some of the populations in the Pacific. We consider M. dianthus (Ellis, 1767), M. exile Hand 1955, M. huanghaiense Pei, 1998, and M. sinensis Pei, 1998 to be junior synonyms of M. senile. We clarify the differences between M. senile and M. farcimen, and comment on the status of M. canum Stuckey, 1914. [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]

We present a genome assembly from an individual Metridium senile (the brown sea anemone; Cnidaria; Anthozoa; Actiniaria; Metridiidae). The genome sequence is 390.9 megabases in span. Most of the assembly is scaffolded into 16 chromosomal pseudomolecules. The mitochondrial genome has also been assembled and is 17.44 kilobases in length.

The attention towards non-native sea anemone introductions has been steadily increasing as multiple species are reported from new locations each year. However, a lack of monitoring efforts and difficulties associated with the detection and identification of these species may result in overlooking introductions in certain areas. In the southern hemisphere, one of these non-native species is Metridium senile, whose current taxonomic and invasion status in Argentina is unclear. Here, we pooled scientific and community records to shed light on the past, current and future invasion scenario of this species. First, we clarified the taxonomic and invasion status of suspected M. senile populations from Argentina by revising available morphological descriptions and attributes associated with non-native species. Then, we inferred and described the potential dispersal pattern in Argentina from the late 1890s to present day. Finally, we provided a forecast of the species potential distribution range in the Southwestern Atlantic Ocean, along the coast and in off-shore areas. Enough evidence suggests that M. senile is a non-native species that has successfully established in Argentina. This species has been mistakenly considered as native for decades due to taxonomic errors and historical and geographical gaps (i.e., pseudoindigenous species). Its current distribution range in Argentina covers over 2000 km of coastline with a southward expansion in recent years. Moreover, according to our forecasted potential distribution, this species can spread further and reach novel areas in coastal and off-shore locations. As M. senile combines multiple traits of a successful invader, monitoring efforts should be implemented to early detect or prevent its establishment in areas recently colonized or at risk. [ABSTRACT FROM AUTHOR]

Phylum Cnidaria represents a unique group among venomous taxa, with its delivery system organised as individual organelles, known as nematocysts, heterogeneously distributed across morphological structures rather than packaged as a specialised organ. Acontia are packed with large nematocysts that are expelled from sea anemones during aggressive encounters with predatory species and are found in a limited number of species in the superfamily Metridioidea. Little is known about this specialised structure other than the commonly accepted hypothesis of its role in defence and a rudimentary understanding of its toxin content and activity. This study utilised previously published transcriptomic data and new proteomic analyses to expand this knowledge by identifying the venom profile of acontia in Calliactis polypus. Using mass spectrometry, we found limited toxin diversity in the proteome of acontia, with an abundance of a sodium channel toxin type I, and a novel toxin with two ShK-like domains. Additionally, genomic evidence suggests that the proposed novel toxin is ubiquitous across sea anemone lineages. Overall, the venom profile of acontia in Calliactis polypus and the novel toxin identified here provide the basis for future research to define the function of acontial toxins in sea anemones. [ABSTRACT FROM AUTHOR]

Sea anemones (Actiniaria) are among the rarest of recognized fossil organisms, even rarer than jellyfish. Here we demonstrate that the most abundant fossil in the Pennsylvanian Mazon Creek Lagerstätte of Illinois, Essexella asherae, is an infaunal or semi‐infaunal anemone. Essexella is redescribed based on a taphonomic analysis of thousands of specimens, as well as associated medusae and trace fossils. Specimens of Essexella (also known as the 'blobs') were long believed to be medusae, but we reassign Essexella to the order Actiniaria and reinterpret the putative jellyfish Reticulomedusa as the pedal or oral disc of Essexella. We also implicate Essexella as a producer of Conostichus, a widespread plug‐shaped trace fossil that occurs in coeval strata in the same region. Radiate structures comparable to the bases of Conostichus and the ichnofossil Bergaueria, as well as the pedal discs of modern anemones, characterize Reticulomedusa. Bona fide medusae are present in the Mazon Creek biota, and include Anthracomedusa turnbulli and Octomedusa pieckorum, whereas the soft‐bodied fossil Lascoa mesostaurata is referred to Problematica. [ABSTRACT FROM AUTHOR]

Bunodeopsis pelagica is one of the few species of sea anemones known to be found in the floating algae of Sargassum spp. It has been reported in the North Atlantic, particularly in the Canary Islands and the coast of Jamaica. The present study is the first to report the occurrence of B. pelagica in the Mexican Atlantic, found as epiphyte on Sargassum natans off Alacranes reef (southern Gulf of Mexico) and in Puerto Morelos reef (Mexican Caribbean), revealing that this species is much more widespread than has been reported. Bunodeopsis pelagica is mainly distinguished from other species of Bunodeopsis by having simple minute protuberances on its column, while its congeners have larger and much more developed vesicular projections. With the record of B. pelagica , the number of known species of actiniarian sea anemones from the Mexican Atlantic increases to 23. [ABSTRACT FROM AUTHOR]

[Display omitted] • Sea anemone diversity is understudied at a regional level for French Polynesia and at a local level for the island of Moorea. • Target capture of ultra-conserved elements is more reliable in lineages where conventional mitochondrial barcodes fail, such as Actiniaria. • Phylogenetic identification of sea anemone samples collected during a "BioBlitz" recovers the genera Andvakia and Aiptasiomorpha for the first time in Moorea. Sea anemones (Order Actiniaria) are a diverse group of marine invertebrates ubiquitous across marine ecosystems. Despite their wide distribution and success, a knowledge gap persists in our understanding of their diversity within tropical systems, owed to sampling bias of larger and more charismatic species overshadowing cryptic lineages. This study aims to delineate the sea anemone diversity in Mo'orea (French Polynesia) with the use of a dataset from the Mo'orea Biocode's "BioBlitz" initiative, which prioritized the sampling of more cryptic and understudied taxa. Implementing a target enrichment approach, we integrate 71 newly sequenced samples into an expansive phylogenetic framework and contextualize Mo'orea's diversity within global distribution patterns of sea anemones. Our analysis corroborates the presence of several previously documented sea anemones in French Polynesia and identifies for the first time the occurrence of members of genera Andvakia and Aiptasiomorpha. This research unveils the diverse sea anemone ecosystem in Mo'orea, spotlighting the area's ecological significance and emphasizing the need for continued exploration. Our methodology, encompassing a broad BLAST search coupled with phylogenetic analysis, proved to be a practical and effective approach for overcoming the limitations posed by the lack of comprehensive sequence data for sea anemones. We discuss the merits and limitations of current molecular methodologies and stress the importance of further research into lesser-studied marine organisms like sea anemones. Our work sets a precedent for future phylogenetic studies stemming from BioBlitz endeavors. [ABSTRACT FROM AUTHOR]

New in situ records of the sublittoral sea anemone Oulactis coliumensis (Riemann-Zürneck & Gallardo, 1990) are provided from different localities of northern Chile and Peru. Specimens were generally observed buried in shallow soft bottoms (3–25 m depth), near port cities and in areas with a high organic load. This is the first report of the species outside its type locality (off the Bay of Coliumo, Chile; ~36°S), extending its range of distribution to lower latitudes. [ABSTRACT FROM AUTHOR]

Phylum Cnidaria represents a unique group among venomous taxa, with its delivery system organised as individual organelles, known as nematocysts, heterogeneously distributed across morphological structures rather than packaged as a specialised organ. Acontia are packed with large nematocysts that are expelled from sea anemones during aggressive encounters with predatory species and are found in a limited number of species in the superfamily Metridioidea. Little is known about this specialised structure other than the commonly accepted hypothesis of its role in defence and a rudimentary understanding of its toxin content and activity. This study utilised previously published transcriptomic data and new proteomic analyses to expand this knowledge by identifying the venom profile of acontia in Calliactis polypus. Using mass spectrometry, we found limited toxin diversity in the proteome of acontia, with an abundance of a sodium channel toxin type I, and a novel toxin with two ShK-like domains. Additionally, genomic evidence suggests that the proposed novel toxin is ubiquitous across sea anemone lineages. Overall, the venom profile of acontia in Calliactis polypus and the novel toxin identified here provide the basis for future research to define the function of acontial toxins in sea anemones.

Abstract Background Numerous deep-sea invertebrates, at both hydrothermal vents and methane seeps, have formed symbiotic associations with internal chemosynthetic bacteria in order to harness inorganic energy sources typically unavailable to animals. Despite success in nearly all marine habitats and their well-known associations with photosynthetic symbionts, Cnidaria remain one of the only phyla present in the deep-sea without a clearly documented example of dependence on chemosynthetic symbionts. Results A new chemosynthetic symbiosis between the sea anemone Ostiactis pearseae and intracellular bacteria was discovered at ~ 3700 m deep hydrothermal vents in the southern Pescadero Basin, Gulf of California. Unlike most sea anemones observed from chemically reduced habitats, this species was observed in and amongst vigorously venting fluids, side-by-side with the chemosynthetic tubeworm Oasisia aff. alvinae. Individuals of O. pearseae displayed carbon, nitrogen, and sulfur tissue isotope values suggestive of a nutritional strategy distinct from the suspension feeding or prey capture conventionally employed by sea anemones. Molecular and microscopic evidence confirmed the presence of intracellular SUP05-related bacteria housed in the tentacle epidermis of O. pearseae specimens collected from 5 hydrothermally active structures within two vent fields ~ 2 km apart. SUP05 bacteria (Thioglobaceae) dominated the O. pearseae bacterial community, but were not recovered from other nearby anemones, and were generally rare in the surrounding water. Further, the specific Ostiactis-associated SUP05 phylotypes were not detected in the environment, indicating a specific association. Two unusual candidate bacterial phyla (the OD1 and BD1-5 groups) appear to associate exclusively with O. pearseae and may play a role in symbiont sulfur cycling. Conclusion The Cnidarian Ostiactis pearseae maintains a physical and nutritional alliance with chemosynthetic bacteria. The mixotrophic nature of this symbiosis is consistent with what is known about other cnidarians and the SUP05 bacterial group, in that they both form dynamic relationships to succeed in nature. The advantages gained by appropriating metabolic and structural resources from each other presumably contribute to their striking abundance in the Pescadero Basin, at the deepest known hydrothermal vents in the Pacific Ocean.

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]

Although the biometric investigation of the cnidome represents an essential diagnostic feature to successfully identify cnidarian species, further efforts are needed to fully characterize eventual differences. Important model actiniarians, such Anemonia viridis and Aiptasia spp., are commonly used for scientific purposes; however, their identification is often difficult, and the description of their cnidome is, therefore, essential. To contribute to this necessity, specimens of Anemonia viridis and Aiptasia couchii from the North Adriatic Sea were collected to acquire data (i.e. length, width, size range, length/width ratio) about cnidae from different tissues (i.e. column, tentacles, actinopharynx, mesenteries, and acrorhagi/acontia). Four types of cnidae were observed in each species. A. viridis shows microbasic b-mastigophores, microbasic p-mastigophores, holotrichous isorhizas, and spirocysts, whereas A. couchii harbored basitrichs, microbasic p-mastigophore, microbasic p-amastigophore and spirocysts. Molecular and phylogenetic analyses were also performed using three mitochondrial markers to confirm the correct classification of the specimens here analysed. [ABSTRACT FROM AUTHOR]

Background: Numerous deep-sea invertebrates, at both hydrothermal vents and methane seeps, have formed symbiotic associations with internal chemosynthetic bacteria in order to harness inorganic energy sources typically unavailable to animals. Despite success in nearly all marine habitats and their well-known associations with photosynthetic symbionts, Cnidaria remain one of the only phyla present in the deep-sea without a clearly documented example of dependence on chemosynthetic symbionts. Results: A new chemosynthetic symbiosis between the sea anemone Ostiactis pearseae and intracellular bacteria was discovered at ~ 3700 m deep hydrothermal vents in the southern Pescadero Basin, Gulf of California. Unlike most sea anemones observed from chemically reduced habitats, this species was observed in and amongst vigorously venting fluids, side-by-side with the chemosynthetic tubeworm Oasisia aff. alvinae. Individuals of O. pearseae displayed carbon, nitrogen, and sulfur tissue isotope values suggestive of a nutritional strategy distinct from the suspension feeding or prey capture conventionally employed by sea anemones. Molecular and microscopic evidence confirmed the presence of intracellular SUP05-related bacteria housed in the tentacle epidermis of O. pearseae specimens collected from 5 hydrothermally active structures within two vent fields ~ 2 km apart. SUP05 bacteria (Thioglobaceae) dominated the O. pearseae bacterial community, but were not recovered from other nearby anemones, and were generally rare in the surrounding water. Further, the specific Ostiactis-associated SUP05 phylotypes were not detected in the environment, indicating a specific association. Two unusual candidate bacterial phyla (the OD1 and BD1-5 groups) appear to associate exclusively with O. pearseae and may play a role in symbiont sulfur cycling. Conclusion: The Cnidarian Ostiactis pearseae maintains a physical and nutritional alliance with chemosynthetic bacteria. The mixotrophic nature of this symbiosis is consistent with what is known about other cnidarians and the SUP05 bacterial group, in that they both form dynamic relationships to succeed in nature. The advantages gained by appropriating metabolic and structural resources from each other presumably contribute to their striking abundance in the Pescadero Basin, at the deepest known hydrothermal vents in the Pacific Ocean. [ABSTRACT FROM AUTHOR]

The International Commission on Zoological Nomenclature has declined to use its plenary power to reverse Opinion 2404 regarding Case 3633 which would have resulted in giving priority to the species-group name Dysactis pallida Agassiz in Verrill, 1864 (currently Exaiptasia pallida) over Dysactis diaphanaRapp, 1829 (currently Exaiptasia diaphana). As a result, the Ruling given in Opinion 2404 stands and the species-group name pallida Agassiz in Verrill, 1864, as published in the binomen Dysactis pallida, will not be given precedence over the species-group name diaphanaRapp, 1829, as published in the binomen Actinia diaphana, whenever the two are considered synonyms. [ABSTRACT FROM AUTHOR]

Haliactis arctica is a poorly known species of sea anemone of the family Halcampactinidae known only from the Arctic. So far, there have been no reports of it after the original description, based on a few specimens from Greenland, Spitsbergen, the Barents Sea, Novaya Zemlya and the Chukchi Sea. The rich collection of the Zoological Institute RAS, which includes more than 100 specimens, has allowed a detailed morpho-anatomical study of this sea anemone. Examination of the external and internal morphology of H. arctica indicates a noticeable variability of structural features, especially the retractor muscles, parietal muscles and acontia. Comparison of characters between H. arctica with the other representatives of Halcampactinidae shows significant differences in the organization of these anemones. Their morphological differences and also significant geographic remoteness suggest that they should be attributed to different families, however, at present it is impossible to conduct thorough molecular genetic studies that can confirm or refute this assumption. [ABSTRACT FROM AUTHOR]

Se conoce la biología reproductiva de algunas especies de Actiniaria; este trabajo trata sobre la reproducción de Pseudoparactis tenuicollis Mc Murrich, 1904. Durante los meses de primavera, esta especie presenta una reproducción asexual rápida y todo este proceso tiene lugar en el caparazón del molusco (Brachidontes rodriguezii). Se agregan algunos relatos de la ecología de esta especie e ilustraciones de la anatomía.

As part of a biodiversity study on intertidal invertebrates, several sea anemones from the west coast of the Baja California Peninsula were collected in June 2016. The taxonomic features of four specimens agree well with those of the species Anthopleura radians, a recently described sea anemone from northern Chile. This study is the first published report on this species outside the range of distribution documented in the original description, including new images of A. radians' external and internal features and complete characterization of their cnidae. Differences between A. radians from other species of the genus reported from the eastern Pacific are also discussed. [ABSTRACT FROM AUTHOR]

Widespread non-native species tend to demonstrate an apparent lack of selectivity in habitat requirements, feeding regimes, and reproductive needs, while displaying a tendency to thrive in human-modified habitats. The high phenotypic plasticity typical of sessile, substrate-attached marine species may enhance their chances of survival and spread in a new region. Anthropogenic activities have changed marine habitats over a wide range of phenomena, including water temperature, community species composition, and the types of available substrates, creating new physical and biotic regimes that may contribute to the potential for successful species introduction. Here we examine ten species of sea anemones that have been introduced outside of their native range, and elucidate specific characteristics that are common among globally introduced sea anemones. Various life history strategies enable these species to survive and flourish through transport, introduction, establishment and spread, leading to the successful colonization of a new geographic area. Considering life history strategies and weighing of vector potential, we suggest conditions that facilitate introduction of these species, and identify species of sea anemones that may be introduced in the future in the face of changing climate and increased anthropogenic activities. [ABSTRACT FROM AUTHOR]

In this paper, we explore spatial patterns of shallow-water sea anemones in the Southwest Atlantic (SWA). The following hypotheses were tested: (1) the distribution of sea anemones (Actiniaria and Corallimorpharia) corroborates SWA biogeographic provinces, (2) their distribution presents a richness peak at mid-latitudes, and (3) temperature is the main abiotic driver that structures their species composition. Occurrences/registries were obtained mainly from published sources. We adopted Sørensen dissimilarity and cluster analyses to compare fauna compositions. To verify latitudinal richness patterns, we used a Hill’s numbers approach through rarefaction and extrapolation techniques. Partial redundancy analysis was performed to identify which drivers contribute more to the distribution. The sea anemone faunas are congruent with the following SWA provinces: Brazilian province (BP, 0 to 33° S), Argentinian province (36 to 43° S), and Patagonian province (43 to 56° S), and all differ from the Caribbean province (CP). Although there is a high similarity among the BP and the CP, they form significant clusters with well-supported endemism levels (> 19%). An elevated richness was found at 19–23° S, in the BP southeast (34 spp. and 13% of endemism), supporting an SWA biodiversity center. Temperature explained 64% of the distribution, and the Amazonas-Orinoco and La Plata estuaries act as soft barriers. The sea anemone distribution can be explained by features of the local current systems, combined with isolation through barriers and different ecological tolerances. Furthermore, the patterns reported herein (unprecedented for the group) are similar to those of other marine taxa. A transition zone between tropical and subtropical waters indicates diversity and species accumulation in the SWA. [ABSTRACT FROM AUTHOR]

Metridium senile is a circumboreally distributed sea anemone (Cnidaria: Anthozoa: Actiniaria) native to the northern hemisphere, and has been presumed as introduced to several locations in the southern hemisphere. Although the sea anemone fauna of the Falkland Islands is not well known, to date no historical records of Metridium senile exist. In 2019, we conducted biodiversity surveys to gather information about sea anemones present in the islands. During these 2019 surveys, we detected M. senile from three locations: Stanley (eastern Falklands), the Bird Island (south-west Falklands), and in the northern Jason Islands (north-west Falklands). The species was well established at each location, with evidence for asexual reproduction occurring in the western sites. We confirmed the identification by morphology and DNA analysis. Stanley populations are distinct in color variation from the southwestern and northwestern populations, which may indicate separate introduction waves or pathways and the potential for additional, undetected locations of M. senile. [ABSTRACT FROM AUTHOR]

Anthopleura mariae sp. nov. is a new species of sea anemone (Actiniaria: Actiniidae) from the rocky intertidal of Punta Morro, Baja California, and Punta Eugenia Baja California Sur, México. This species is characterized by a column with verrucae arranged in longitudinal rows from margin to limbus with a red spot atop each verruca, as well as the presence of more than two siphonoglyphs and the lack of directive mesenteries. Differences between Anthopleura mariae sp. nov. with other species of the genus are discussed. This is the sixth species of Anthopleura documented for the Mexican Pacific. [ABSTRACT FROM AUTHOR]

Aim: The mutualistic relationship between anemones and anemonefishes is one of the most iconic examples of symbiosis. However, while anemonefishes have been extensively studied in terms of genetic connectivity, such information is lacking entirely for host sea anemones. Here, we provide the first information on the broad‐scale population structure and phylogeographical patterns of three species of host sea anemone, Heteractis magnifica, Stichodactyla mertensii and Entacmaea quadricolor. We evaluate if there is concordance in genetic structure across several distinct biogeographical areas within the Indo‐Pacific region and to what extent the observed patterns may concur with those found for anemonefishes. Location: Indo‐Pacific, including the Red Sea. Taxon: Heteractis magnifica, S. mertensii and E. quadricolor Methods: Microsatellite markers and a combination of statistical methods including Bayesian clustering, isolation by distance (IBD), analysis of molecular variance (AMOVA) and principal components analysis (PCA) were used to determine population structure. The congruence among distance matrices (CADM) method was used to assess similarity in spatial genetic patterns among species. Results: Significant population structure was identified in the three host anemone species. Each species is likely composed of at least two genetic clusters corresponding to two biogeographical regions, the Red Sea and the rest of the Indo‐Pacific. Two of the three anemone species seem to be experiencing admixture where the two main clusters overlap (the Maldives). IBD analyses in the Red Sea revealed differences in gene flow among species, suggesting more limited dispersal potential for E. quadricolor than for S. mertensii and H. magnifica. Clonality is documented in S. mertensii for the first time. Main conclusions: This research documents the genetic population structure for three ecologically important host sea anemones across the Indo‐Pacific and provides valuable insights regarding their biogeography and evolution. Specifically, we found high levels of genetic divergence between populations across different biogeographical regions, suggesting different evolutionary lineages within species. At the same time, common geographical overlap of population structures suggests similar evolutionary histories among all three species. Interestingly, the observed patterns are congruent to some extent with structure reported for several anemonefish species, reflecting their close ecological association. [ABSTRACT FROM AUTHOR]

Within tropical coastal habitats such as coral reefs and seagrass meadows, sea anemones (Actiniaria) provide microhabitats for a diverse range of fauna. However, the mechanisms that enable these interactions, and how actiniarian diversity and abundance mediates associate assemblages, remains poorly understood. Here, we compared sea anemone species richness and abundance with that of their associated decapod crustaceans and teleost fishes across adjacent coral reef and seagrass habitats at Carrie Bow Cay, Belize. At least 16 decapod and seven fish species were associated with anemones across both habitats, including several previously undocumented associations. While overall anemone-associate richness did not differ between habitats, seagrass anemones had the greatest mean abundance and diversity of both decapod and fish associates. This suggests that the importance of anemones as microhabitat reflected broader benthic complexity and shelter availability, with species aggregating on sea anemones when access to alternative shelter, such as corals, was limited. Patterns of associate distributions on anemones were also highly structured, in terms of both associate and anemone species, with these patterns likely reflecting a combination of associate specialization, intraspecific competition, and anemone morphology and toxicity. The diverse multi-species associate complexes observed suggest that sea anemones provide an important refuge for both specialized and generalist species and so have the potential to increase faunal diversity and abundance within tropical coastal habitats. [ABSTRACT FROM AUTHOR]

The peculiarities of the survival and adaptation of deep-sea organisms raise interest in the study of their metabolites as promising drugs. In this work, the hemolytic, cytotoxic, antimicrobial, and enzyme-inhibitory activities of tentacle extracts from five species of sea anemones (Cnidaria, orders Actiniaria and Corallimorpharia) collected near the Kuril and Commander Islands of the Far East of Russia were evaluated for the first time. The extracts of Liponema brevicorne and Actinostola callosa demonstrated maximal hemolytic activity, while high cytotoxic activity against murine splenocytes and Ehrlich carcinoma cells was found in the extract of Actinostola faeculenta. The extracts of Corallimorphus cf. pilatus demonstrated the greatest activity against Ehrlich carcinoma cells but were not toxic to mouse spleen cells. Sea anemones C. cf. pilatus and Stomphia coccinea are promising sources of antimicrobial and antifungal compounds, being active against Gram-positive bacteria Bacillus subtilis, Staphylococcus aureus, and yeast Candida albicans. Moreover, all sea anemones contain α-galactosidase inhibitors. Peptide mass fingerprinting of L. brevicorne and C. cf. pilatus extracts provided a wide range of peptides, predominantly with molecular masses of 4000–5900 Da, which may belong to a known or new structural class of toxins. The obtained data allow concluding that deep-sea anemones are a promising source of compounds for drug discovery.

Phylum Cnidaria is an ancient venomous group defined by the presence of cnidae, specialised organelles that serve as venom delivery systems. The distribution of cnidae across the body plan is linked to regionalisation of venom production, with tissue-specific venom composition observed in multiple actiniarian species. In this study, we assess whether morphological variants of tentacles are associated with distinct toxin expression profiles and investigate the functional significance of specialised tentacular structures. Using five sea anemone species, we analysed differential expression of toxin-like transcripts and found that expression levels differ significantly across tentacular structures when substantial morphological variation is present. Therefore, the differential expression of toxin genes is associated with morphological variation of tentacular structures in a tissue-specific manner. Furthermore, the unique toxin profile of spherical tentacular structures in families Aliciidae and Thalassianthidae indicate that vesicles and nematospheres may function to protect branched structures that host a large number of photosynthetic symbionts. Thus, hosting zooxanthellae may account for the tentacle-specific toxin expression profiles observed in the current study. Overall, specialised tentacular structures serve unique ecological roles and, in order to fulfil their functions, they possess distinct venom cocktails.

A hallmark of sea anemone mitochondrial genomes (mitogenomes) is the presence of complex catalytic group I introns. Here, we report the complete mitogenome and corresponding transcriptome of the carpet sea anemone Stichodactyla haddoni (family Stichodactylidae). The mitogenome is vertebrate-like in size, organization, and gene content. Two mitochondrial genes encoding NADH dehydrogenase subunit 5 (ND5) and cytochrome c oxidase subunit I (COI) are interrupted with complex group I introns, and one of the introns (ND5-717) harbors two conventional mitochondrial genes (ND1 and ND3) within its sequence. All the mitochondrial genes, including the group I introns, are expressed at the RNA level. Nonconventional and optional mitochondrial genes are present in the mitogenome of S. haddoni. One of these gene codes for a COI-884 intron homing endonuclease and is organized in-frame with the upstream COI exon. The insertion-like orfA is expressed as RNA and translocated in the mitogenome as compared with other sea anemones. Phylogenetic analyses based on complete nucleotide and derived protein sequences indicate that S. haddoni is embedded within the family Actiniidae, a finding that challenges current taxonomy.

Abstract Mitochondrial genome organization of sea anemones appears conserved among species and families, and is represented by a single circular DNA molecule of 17 to 21 kb. The mitochondrial gene content corresponds to the same 13 protein components of the oxidative phosphorylation (OxPhos) system as in vertebrates. Hallmarks, however, include a highly reduced tRNA gene repertoire and the presence of autocatalytic group I introns. Here we demonstrate that the mitochondrial genome of the deep-water sea anemone Protanthea simplex deviates significantly from that of other known sea anemones. The P. simplex mitochondrial genome contains a heavily scrambled order of genes that are coded on both DNA strands and organized along two circular mito-chromosomes, MCh-I and MCh-II. We found MCh-I to be representative of the prototypic sea anemone mitochondrial genome, encoding 12 OxPhos proteins, two ribosomal RNAs, two transfer RNAs, and a group I intron. In contrast, MCh-II was found to be a laterally transferred plasmid-like DNA carrying the conserved cytochrome oxidase II gene and a second allele of the small subunit ribosomal RNA gene. Highlights • The mtDNA consists of two circular mito-chromosomes; MCh-I and MCh-II. • MCh-I resembles a typical sea anemone mtDNA, but lacks the CO II gene. • MCh-I gene order is heavily rearranged and both DNA strands contain genes. • MCh-I contains a giant group I intron element of 15 kb within the ND5 gene. • MCh-II provides the CO II gene, and appears laterally transferred. [ABSTRACT FROM AUTHOR]

Metridium senile, the fluffy (or plumose) sea anemone, is a circumboreal species adapted to the cold northern oceans. We performed a 40-day experiment on 108 individuals of M. senile collected from the Akkeshi-ko estuary in Japan to test their survivability in higher temperatures and their upper and lower salinity survivability limits. In addition to using survivorship to determine if there is a smaller tolerance range than the extreme limits of temperature and salinity, we used asexual reproduction via pedal laceration as an indicator of the most favorable environmental conditions for M. senile. The resulting limitations are used to both broaden our understanding of the biology of M. senile and to assess potential effects of changing oceanic conditions, since M. senile is unable to survive in warm water temperatures or in extreme salinities. Our results support the use of pedal laceration by M. senile as a way to quickly colonize an area with favorable environmental conditions in order to preserve a well-adapted phenotype. [ABSTRACT FROM AUTHOR]

This dissertation: 1) determines the factor(s) responsible for spawning induction in Nematostella vectensis; 2) isolates, describes, and documents the source of jelly from egg masses of N. vectensis; and 3) describes N. vectensis' early development.Nematostella vectensis were maintained on a 7-day mussel feeding/water change regime over 159 days. Within 36 hours of mussel feeding/water change, 69.1% of females and 78.5% of males spawned reliably. Through manipulation of feeding, water change, oxygen and nitrogenous waste concentrations, spawning induction was found to be triggered by the oxygen concentration associated with water change, and not by feeding. Ammonia, anemones' major waste product, inhibited this induction in a concentration-dependent manner.Female N. vectensis release eggs in a persistent jellied egg mass which is unique among the Actiniaria. The major component of this egg mass jelly was a positive periodic acid-Schiffs staining, 39.5-40.5 kD glycoprotein. Antibodies developed in rabbits against this glycoprotein bound to jelly of intact egg masses and to granules (2.8 1-1m in diameter) present in female anemone mesenteries and their associated filaments. Antibodies did not label male tissues.Nematostella vectensis embryos underwent first karyokinesis -60 minutes following the addition of sperm to eggs. Second nuclear division took place, followed by first cleavage, 90-120 minutes later. Each of the 4 blastomeres that resulted from first cleavage contained a single nucleus. Arrangement of these blastomeres ranged from radial to pseudospiral. Embryonic development was both asynchronous and holoblastic. Following formation of the 4-cell stage, 71% of embryos proceeded to cleave again to form an 8-cell stage. In each of the remaining 29% of embryos, a fusion of from 2-4 blastomeres resulted in 4 possible patterns which had no affect on either cleavage interval timing or subsequent development. The fusion event was not due to ooplasmic segregation. Blastomeres isolated from 4-celled embryos were regulative and developed into normal planula larvae and juvenile anemones that were 1/4 the size of those that developed from intact 4-celled embryos. Embryos exhibiting the fusion phenomenon were examined at the fine structural level. The fusion phenomenon resulted in formation of a secondary syncytium and was not a mere compaction of blastomeres.

The objective of this study is to provide information about a harbour-fouling community dominated by Metridium senile in southern Patagonia. Several steel tubes from the wharf of Puerto San Julián were extracted to perform repair tasks, allowing the attached benthic community to be studied. Sampling was conducted at three levels: lower intertidal, 3-4 m depth and 6-7 m depth. In the lower intertidal, M. senile had a relative abundance of 43%, the most abundant accompanying species being Perumytilus purpuratus, Mytilus edulis platensis and Aulacomya atra atra. At subtidal level, the anemone showed relative abundances of 64% and 65%, and was accompanied by Monocorophium insidiosum at 3-4 m depth and by polychaetes of families Sabellidae and Syllidae at 6-7 m at depth. In the lower intertidal, epibiosis was more frequent on P. purpuratus, A. atra atra and M. edulis platensis, while in the subtidal, the richness of substrate-organisms increased significantly and the anemone was fixed to A. atra atra, M. edulis platensis, Paramolgula gregaria, Crepipatella dilatata, Austromegabalanus psittacus, Hiatella arctica, Polyzoa opuntia, Pyura sp. and Sabellidae tubes. The ability of M. senile to settle on many different organisms, along with other strategies, makes it a colonizer able to displace other species that could compete with it for substratum. Given the cosmopolitan nature of M. senile, the fact that this species has not been previously reported in the coastal zone of the region, and the results of our study, we discuss the possibility that this sea anemone is an invasive alien species in southern Patagonia, or at least a cryptogenic species.

We present a genome assembly from an individual Metridium senile (the brown sea anemone; Cnidaria; Anthozoa; Actiniaria; Metridiidae). The genome sequence is 390.9 megabases in span. Most of the assembly is scaffolded into 16 chromosomal pseudomolecules. The mitochondrial genome has also been assembled and is 17.44 kilobases in length., Competing Interests: No competing interests were disclosed., (Copyright: © 2023 Adkins P et al.)

Sea anemones (Order Actiniaria) are among the most diverse members of the subclass Hexacorallia and are an emerging model system. Unfortunately, defining species and creating robust phylogenies remain a serious challenge due to simple body plans that reduce the number of available morphological characters, slow mitochondrial sequence evolution and a complete absence of nuclear markers in the actiniarian molecular toolkit other than the ribosomal cistron. Defining species boundaries and phylogenetic relationships is imperative for advancing our understanding of sea anemone taxonomy and systematics. Herein, we utilized EPIC (exon‐priming intron‐crossing) primers, in addition to non‐standard PCR profiling conditions, to obtain sequence data for seven nuclear introns located within Calmodulin, Calpain, Nck Associated Protein 1 Homolog, Pescadillo Homolog, Signal Recognition Particle 54‐kDa Subunit, Transferase and Vacuolar ATP Synthase Subunit B. These new markers were employed to evaluate whether morphological variability in marginal tentacle protuberances is indicative of intraspecific variation or cryptic species in the shallow‐water anemone Phymanthus crucifer. Variability within these nuclear introns was compared to mitochondrial 12S, 16S and cox3, and nuclear 18S and 28S. PCR products of all nuclear introns were cloned to determine copy number and the resulting variability among clones was consistent with single‐copy markers. We also amplified and sequenced six of the seven introns in a sister species, Phymanthus loligo, to determine the degree of interspecific variation. In addition, we evaluate the applicability of a subset of these markers within Actinostola and conclude with a review of putative single‐copy markers used in octocoral and scleractinian phylogenetics. [ABSTRACT FROM AUTHOR]

The phylogenetic resolution provided by genome-wide data has demonstrated the usefulness of RAD sequencing to tackle long-standing taxonomic questions. Cnidarians have recently become a model group in this regard, yet species delimitation analyses have been mostly performed in octocorals. In this study, we used RAD sequencing to test the species hypotheses in a wide-spread complex of sea anemones (genus Anthothoe ), contrasting this new line of evidence with their current classification. The alternative hypotheses were tested using a Bayes Factors delimitation method, and the most probable species tree was then evaluated under different biogeographic scenarios. Our results decisively rejected the current morphology-informed delimitation model and infer the presence of several cryptic species associated with distinct marine ecoregions. This spatial pattern was remarkably consistent throughout the study, highlighting the role of geographic distribution as a powerful explanatory variable of lineages diversification. The southern Gondwana pattern with episodic, jump dispersal events is the biogeographic historical representation that best fits the Anthothoe species tree. The high population differentiation possibly amplified by the occurrence of asexual reproduction makes it difficult to identify genes responsible for local adaptation, however, these seem to be mainly associated with cellular and metabolic processes. We propose a new set of species hypotheses for the Southern Hemispheric Anthothoe clade, based on the pronounced genomic divergence observed among lineages. Although the link between the genetic and phenotypic differentiation remains elusive, newer sequencing technologies are bringing us closer to understanding the evolution of sea anemone diversity and, therefore, how to appropriately classify them. [ABSTRACT FROM AUTHOR]

Knowledge of ecological interactions is integral for informed management, especially in the rapidly changing Antarctic marine ecosystem. Nonetheless, even basic ecological relationships are unknown for most benthic species, including conspicuous predatory species such as sea anemones. The aim of this study is to understand the ecology of sea anemones in the Terre Adélie region. Using video footage collected by remote operated vehicle (ROV), we examined sea anemone distribution and abundance in relation to predator and prey abundance, presence of other taxa and habitat structure. The ROV was deployed over ten different transects with depths ranging from 32 to 251 m. A total of 332 sea anemones were observed across 6.6 km2 of seabed surveyed. We compared sea anemone abundance with habitat type and substrate attachment. Multivariate analysis in PRIMER was used to examine community composition. Sea anemone density was not significantly associated with habitat types. However, sea anemones were associated with the biogenic substrates, ascidians and bryozoans. This association suggests a potential future vulnerability for Antarctic sea anemones if bryozoan and ascidian distributions are impacted by climate change-associated ecosystem disturbances. [ABSTRACT FROM AUTHOR]

The mitochondrial genomes of sea anemones are dynamic in structure. Invasion by genetic elements, such as self-catalytic group I introns or insertion-like sequences, contribute to sea anemone mitochondrial genome expansion and complexity. By using next generation sequencing we investigated the complete mtDNAs and corresponding transcriptomes of the temperate sea anemone Anemonia viridis and its closer tropical relative Anemonia majano . Two versions of fused homing endonuclease gene ( HEG ) organization were observed among the Actiniidae sea anemones; in-frame gene fusion and pseudo-gene fusion. We provided support for the pseudo-gene fusion organization in Anemonia species, resulting in a repressed HEG from the COI-884 group I intron. orfA , a putative protein-coding gene with insertion-like features, was present in both Anemonia species. Interestingly, orfA and COI expression were significantly up-regulated upon long-term environmental stress corresponding to low seawater pH conditions. This study provides new insights to the dynamics of sea anemone mitochondrial genome structure and function. [ABSTRACT FROM AUTHOR]