Global diversity of brittle stars (Echinodermata: Ophiuroidea)

Long-term study of the combined effects of ocean acidification and warming on the mottled brittle star, Ophionereis fasciata

The global ocean is rapidly changing, posing a substantial threat to the viability of marine populations due to the co-occurrence of multiple drivers, such as ocean warming (OW) and ocean acidification (OA). To persist, marine species must undergo some combination of acclimation and adaptation in response to these changes. Understanding such responses is essential to measure and project the magnitude and direction of current and future vulnerabilities in marine ecosystems. Echinoderms have been recognised as a model in studies of OW-OA effects on marine biota. However, despite their global diversity, vulnerability and ecological importance in most marine habitats, brittle stars (ophiuroids) are poorly studied. A long-term mesocosm experiment was conducted on adult mottled brittle star (Ophionereis fasciata) as a case study to investigate the physiological response and trade-offs of marine organisms to ocean acidification, ocean warming and the combined effect of these two drivers. Long-term exposure of O. fasciata to high temperature and low pH affected survival, respiration and regeneration rates, growth rate, calcification/dissolution and righting response. Higher temperatures increased stress and respiration, and decreased regeneration and growth rates as well as survival. Conversely, changes in pH had more subtle or no effect, affecting only respiration and calcification. Our results indicate that exposure to a combination of high temperature and low pH produces complex responses for respiration, righting response and calcification. We address the knowledge gap of the impact of a changing ocean on ophiuroids in the context of echinoderm studies, proposing this class as an ideal alternative echinoderm for future research.

Unveiling ophiuroid biodiversity across North Atlantic habitats via an integrative perspective

The depths of the North Atlantic Ocean host a species-rich fauna providing heterogeneous habitats from thermal vent fields to cold-water coral reefs. With the increasing threat of destruction of deep-sea habitats due to human impacts, such as demersal fishing and the beginning of deep-sea mining, an analysis of the diversity and distribution of species is crucial for conservation efforts. Brittle stars occur in high biomasses, contributing to the biodiversity of the seafloor. Specimens were collected during several scientific expeditions to gain a more detailed insight into the brittle star diversity in the North Atlantic Ocean. An integrative approach to identify the species with DNA barcoding (mtCOI) in combination with morphological studies revealed 24 species. Most species have been previously identified in the North Atlantic, but sequences for 13 species are newly added to public repositories. Additionally, the MALDI-TOF-MS proteomic analysis was successfully applied for 197 specimens with known COI barcodes. Results are congruent with other molecular species delimitations demonstrating the functionality of proteomics for the identification of brittle stars. This dataset significantly expands our understanding of the taxonomic and genetic diversity of brittle stars and contributes to publicly available data. It emphasizes the importance of considering habitat heterogeneity for large scale patterns of biodiversity.

The brittle star genome illuminates the genetic basis of animal appendage regeneration

Species within nearly all extant animal lineages are capable of regenerating body parts. However, it remains unclear whether the gene expression programme controlling regeneration is evolutionarily conserved. Brittle stars are a species-rich class of echinoderms with outstanding regenerative abilities, but investigations into the genetic bases of regeneration in this group have been hindered by the limited genomic resources. Here we report a chromosome-scale genome assembly for the brittle star Amphiura filiformis. We show that the brittle star genome is the most rearranged among echinoderms sequenced so far, featuring a reorganized Hox cluster reminiscent of the rearrangements observed in sea urchins. In addition, we performed an extensive profiling of gene expression during brittle star adult arm regeneration and identified sequential waves of gene expression governing wound healing, proliferation and differentiation. We conducted comparative transcriptomic analyses with other invertebrate and vertebrate models for appendage regeneration and uncovered hundreds of genes with conserved expression dynamics, particularly during the proliferative phase of regeneration. Our findings emphasize the crucial importance of echinoderms to detect long-range expression conservation between vertebrates and classical invertebrate regeneration model systems.

Symbiotic Relationship of Comasterschlegelii (Crinoidea: Comatulidae) and Gymnolophus obscura (Ophiuroidea: Ophiotrichidae) Derived from Stable Isotope and Fatty Acid Analyses

Coral reef community exhibits high species diversity and a broad range of biological relationships, including widespread symbiosis and complex food utilization patterns. In our study, we investigated the symbiotic relationship between the commonly crinoid host Comaster schlegelii and its ophiuroid obligatory symbiont Gymnolophus obscura. Using a combination of fatty acid biomarkers and stable isotopic compositions, we explored differences in their organic matter utilization strategies and nutritional relationships. The result of stable isotopes revealed that G. obscura had higher δ15N values than its crinoid host. Particulate organic matter and phytoplankton were identified as the primary food sources for both species, however C. schlegelii showed a higher proportional contribution from benthic microalgae. Fatty acid markers showed that C. schlegelii was more dependent on benthic microalgae such as diatoms, and less on debritic organic matter and bacteria than G. obscura. Elevated δ15N values of G. obscura and similar food source contribution rates between the host and symbiont suggest that ophiuroid feeds on materials filtered by crinoids and have similar diet to the host. Our results provide insights into the symbiotic patterns of crinoids and ophiuroids, while also supplying foundational data on how symbiotic reef species select organic matter utilization strategies to adapt to their environment.

Fossil evidence for the ancient link between clonal fragmentation, six-fold symmetry and an epizoic lifestyle in asterozoan echinoderms

Asexual reproduction by means of splitting, also called fissiparity, is a common feature in some asterozoan groups, especially in ophiactid brittle stars. Most fissiparous brittle stars show six instead of the usual five rays, live as epibionts on host organisms, and use clonal fragmentation to rapidly colonize secluded habitats and effectively expand the margins of their distribution area. While the biology and ecology of clonal fragmentation are comparatively well understood, virtually nothing is known about the evolution and geological history of that phenomenon. Here, we describe an exceptional fossil of an articulated six-armed brittle star from the Late Jurassic of Germany, showing one body half in the process of regeneration, and assign it to the new species Ophiactis hex sp. nov. Phylogenetic inference shows that the fossil represents the oldest member of the extant family Ophiactidae. Because the Ophiactis hex specimen shows an original six-fold symmetry combined with a morphology typically found in epizoic ophiuroids, in line with recent fissiparous ophiactid relatives, we assume that the regenerating body half is an indication for fissiparity. Ophiactis hex thus shows that fissiparity was established as a means of asexual reproduction in asterozoan echinoderms by the Late Jurassic.

The Cabrières Biota (France) provides insights into Ordovician polar ecosystems

Early Palaeozoic sites with soft-tissue preservation are predominantly found in Cambrian rocks and tend to capture past tropical and temperate ecosystems. In this study, we describe the diversity and preservation of the Cabrières Biota, a newly discovered Early Ordovician Lagerstätte from Montagne Noire, southern France. The Cabrières Biota showcases a diverse polar assemblage of both biomineralized and soft-bodied organisms predominantly preserved in iron oxides. Echinoderms are extremely scarce, while sponges and algae are abundantly represented. Non-biomineralized arthropod fragments are also preserved, along with faunal elements reminiscent of Cambrian Burgess Shale-type ecosystems, such as armoured lobopodians. The taxonomic diversity observed in the Cabrières Biota mixes Early Ordovician Lagerstätten taxa with Cambrian forms. By potentially being the closest Lagerstätte to the South Pole, the Cabrières Biota probably served as a biotic refuge amid the high-water temperatures of the Early Ordovician, and shows comparable ecological structuring to modern polar communities.

Studies on Secondary Metabolites and In vitro and In silico Anticholinesterases Activities of the Sea Urchin Echinometra mathaei Crude Venoms from the Persian Gulf-Bushehr

Background:

Echinoderms are a unique source of amazing secondary metabolites with a wide spectrum of biological activities. Several species of sea urchins contain various toxins and biologically active metabolites. One of the most attractive approaches to treat Alzheimer's disease is searching for effective marine natural products with cholinesterase inhibitory activities.

Objective:

The current study is designed to investigate the in vitro and in silico acetylcholinesterase and butyrylcholinesterase inhibitory activities of the Persian Gulf echinoderm sea urchin Echinometra mathaei venom and related chemical compounds.

Methods:

The experiments for LD50, total protein, protein bands, in vitro cholinesterase inhibitory activities, the identity of secondary metabolites, and the in silico evaluations, respectively, were performed by Spearman-Karber, Lowry, SDS-PAGE, Ellman's spectroscopic, GC-MS, and docking methods.

Results:

The LD50 (IV rat) of the spine, gonad, and coelomic fluid from sea urchin samples were 2.231 ± 0.09, 1.03 ± 0.05, and 1.12 ± 0.13 mg/ml, respectively. The SDS-PAGE and total protein studies showed that at least a portion of the venom is protein in nature. GC-MS analysis of the identified samples revealed 12, 23, and 21 compounds with different chemical types, including alkaloids, terpenes, and steroids, respectively. According to the results, all samples act as significant inhibitors of both enzymes. In silico data for the identified compounds also confirmed the experimental results.

Conclusion:

The alkaloid compound 6H-Indolo[3,2,1-de] [1,5] naphthyridine-6-one,1,2,3a,4,5- hexahydro-8-hydroxy-3-methyl (C7) had the highest affinity for both enzymes. Further research is needed to determine whether C7 could be a therapeutic candidate for Alzheimer's disease.

The correlation between echinoderms diversity and physicochemical parameters in marine pollution: A case study of the Persian Gulf coastline

This study was conducted with the aim of investigating the correlation between echinoderms diversity and physicochemical parameters in the Persian Gulf coastline in Bushehr province in 4 seasons from March to December 2017. The physicochemical parameters including water temperature, dissolved oxygen (DO), electrical conductivity (EC), salinity, pH and turbidity were measured at each sampling location. The results showed a significant correlation between echinoderms diversity and physicochemical parameters. The correlation coefficient of the Astropecten polyacanthus species with the parameters of temperature, DO, EC, salinity and turbidity was reported as -0.41, 0.64, -0.25, -0.44 and 0.60 respectively. This coefficient for the Ophiothrix fragilis species was reported as -0.68, 0.70, -0.21, -0.36 and -0.55 respectively. The results demonstrated that the most sensitive species were Astropecten polyacanthus and Ophiothrix fragilis respectively. The different species of echinoderms can be used as biological indicators of pollution in evaluating the physicochemical quality of marine environments.

Evaluating the secondary bioactive metabolites in Geodia corticostylifera

Abstract Ophiactis savignyi could be discovered all over the world in tropical marine environments. People could have aided in the spread of O. savignyi, particularly in the western and eastern populations of Panama's Isthmus. The brittle star Ophiactis savignyi, often known as savigny's brittle star, coexists alongside the sponge Geodia corticostylifera. The focus of this research has been to assess the functional relevance of G. corticostylifera secondary metabolites as antifoulant against mussels, protection against generalist fish, and chemical cues to affiliated brittle stars. Both in flow-through and static seawater laboratory studies, O. savignyi which has previously been connected with sponges, was given both treated and control mimics at the same time. The sponge extract was also tested for its ability to protect fish against predators and fouling. Deterrence test using chemicals indicated that the normal level of the sponge extract may also suppress generalist fish predation in the field as well as the mussel Perna perna’s normal attachment in clinical contexts. According to the findings, G. corticostylifera crude extract has many roles in the aquatic environments, apparently being accountable for this sponge's tighter relationship with O. savignyi, which protects the ophiuroid and inhibits epibionts on itself.

Exceptional population genomic homogeneity in the black brittle star Ophiocomina nigra (Ophiuroidea, Echinodermata) along the Atlantic-Mediterranean coast

The Atlantic-Mediterranean marine transition is characterised by strong oceanographic barriers and steep environmental gradients that generally result in connectivity breaks between populations from both basins and may lead to local adaptation. Here, we performed a population genomic study of the black brittle star, Ophiocomina nigra, covering most of its distribution range along the Atlantic-Mediterranean region. Interestingly, O. nigra is extremely variable in its coloration, with individuals ranging from black to yellow-orange, and different colour morphs inhabiting different depths and habitats. In this work, we used a fragment of the mitochondrial COI gene and 2,374 genome-wide ddRADseq-derived SNPs to explore: (a) whether the different colour morphs of O. nigra represent different evolutionary units; (b) the disruptive effects of major oceanographic fronts on its population structure; and (c) genomic signals of local adaptation to divergent environments. Our results revealed exceptional population homogeneity, barely affected by oceanographic fronts, with no signals of local adaptation nor genetic differentiation between colour morphs. This remarkable panmixia likely results from a long pelagic larval duration, a large effective population size and recent demographic expansions. Our study unveils an extraordinary phenotypic plasticity in O. nigra, opening further research questions on the ecological and molecular mechanisms underpinning coloration in Ophiuroidea.

Integrative species delimitation in the common ophiuroid Ophiothrix angulata (Echinodermata: Ophiuroidea): insights from COI, ITS2, arm coloration, and geometric morphometrics

Ophiothrix angulata (Say, 1825) is one of the most common and well-known ophiuroids in the Western Atlantic, with a wide geographic and bathymetric range. The taxonomy of this species has been controversial for a century because of its high morphological variability. Here we integrate information from DNA sequence data, color patterns, and geometric morphometrics to assess species delimitation and geographic differentiation in O. angulata. We found three deeply divergent mtDNA-COI clades (K2P 17.0-27.9%). ITS2 nuclear gene and geometric morphometrics of dorsal and ventral arm plates differentiate one of these lineages, as do integrative species delineation analyses, making this a confirmed candidate species.

Evo-Devo in Ophiuroids: The Switch from Planktotrophy to Lecithotrophy in Ophionereis

AbstractUnderstanding the evolution of development (evo-devo) in the Ophiuroidea and the pathways in the switch from a feeding to a nonfeeding larva is complicated by the variability in the phenotype of the metamorphic larva, being a reduced yolky ophiopluteus in some species (type I development) and a vitellaria larva in others (type II development). We investigated evo-devo in the family Ophionereididae, a group dominated by lecithotrophic development through a vitellaria larva. We reared the planktotrophic larvae of Ophionereis fasciata to settlement to determine the metamorphic phenotype. Counter to expectations, O. fasciata did not exhibit type II metamorphosis through a vitellaria, although it did exhibit transient vitellaria-like features. Resorption of the larval arms in the same interradial positions where the ciliary bands form in vitellariae gave them a fleeting vitellaria-like appearance. Development of O. fasciata exhibits heterochronic features in early formation of the skeletal primordium of the third pair (postoral) of larval arms and in the presettlement juvenile early appearance of the juvenile terminal arm plates on external view in parallel with larval arm resorption. Development of the fourth pair (posterodorsal) of larval arms, the last pair to be formed, is plastic, with 44% of larvae exhibiting partial arm growth. Heterochronic traits in development, as seen in O. fasciata, may have facilitated evolution of a lecithotrophic mode of development in Ophionereis. Comparison of the ophiopluteus of O. fasciata and the vestigial pluteus of O. schayeri provided insights into the simplification of larval form from the ancestral (feeding larva) state in Ophionereis. The diverse metamorphic phenotypes in ophiuroids indicate that type I and type II development may not be completely divergent lines of evo-devo and point to selective pressure in the pelagic-benthic transition in the evolution of ophiuroid development.

Astrocharis margarita sp. nov., a new snake star (Echinodermata, Ophiuroidea, Euryalidae) from a seamount in the Western Pacific

During the scientific expedition of the R/V Kexue in 2014, a new species belonging to the genus Astrocharis Koehler, 1904 was collected from a seamount near the Yap Trench. Astrocharis margarita sp. nov. is distinguished from the other species of Astrocharis by the following characters: radial shields are partly naked or completely covered by polygonal ossicles, and the body color is uniformly light pink. Maximum Likelihood Tree and Bayesian Tree, based on a concatenated dataset of COI, 16S, and 18S genes analyses, indicated that the monophyly of Astrocharis was not supported, which suggested the genus needs to be revised.

First report of brittle stars (Echinodermata: Ophiuroidea) from a seamount in the eastern Arabian Sea

This paper reports two species-Ophiozonella molesta (Koehler, 1904) and Ophiothamnus venustus Matsumoto, 1915, from a seamount in the Eastern Arabian Sea. This forms the first ever report of Ophiothamnus venustus from the Indian Ocean, and the first verified report of Ophiozonella molesta from Indian waters. This is the first ever work to document benthic invertebrates from seamounts in the Arabian Sea.

Development of two new sets of PCR primers for eDNA metabarcoding of brittle stars (Echinodermata, Ophiuroidea)

Brittle stars (class Ophiuroidea) are marine invertebrates comprising approximately 2,100 extant species, and are considered to constitute the most diverse taxon of the phylum Echinodermata. As a non-invasive method for monitoring biodiversity, we developed two new sets of PCR primers for metabarcoding environmental DNA (eDNA) from brittle stars. The new primer sets were designed to amplify 2 short regions of the mitochondrial 16S rRNA gene, comprising a conserved region (111–115 bp, 112 bp on average; named “16SOph1”) and a hyper-variable region (180–195 bp, 185 bp on average; named “16SOph2”) displaying interspecific variation. The performance of the primers was tested using eDNA obtained from two sources: a) rearing water of an 2.5 or 170 L aquarium tanks containing 15 brittle star species and b) from natural seawater collected around Misaki, the Pacific coast of central Japan, at depths ranging from shallow (2 m) to deep (> 200 m) sea. To build a reference library, we obtained 16S rRNA sequences of brittle star specimens collected from around Misaki and from similar depths in Japan, and sequences registered in International Nucleotide Sequence Database Collaboration. As a result of comparison of the obtained eDNA sequences with the reference library 37 (including cryptic species) and 26 brittle star species were detected with certain identities by 16SOph1 and 16SOph2 analyses, respectively. In shallow water, the number of species and reads other than the brittle stars detected with 16SOph1 was less than 10% of the total number. On the other hand, the number of brittle star species and reads detected with 16SOph2 was less than half of the total number, and the number of detected non-brittle star metazoan species ranged from 20 to 46 species across 6 to 8 phyla (only the reads at the “Tank” were less than 0.001%). The number of non-brittle star species and reads at 80 m was less than 10% with both of the primer sets. These findings suggest that 16SOph1 is specific to the brittle star and 16SOph2 is suitable for a variety of marine metazoans. It appears, however, that further optimization of primer sequences would still be necessary to avoid possible PCR dropouts from eDNA extracts. Moreover, a detailed elucidation of the brittle star fauna in the examined area, and the accurate identification of brittle star species in the current DNA databank is required.

High polychaete diversity in the Gulf of Guinea (West African continental margin): The influence of local and intermediate scale ecological factors on a background of regional patterns

The Tropical East Atlantic is one of the least studied areas in the world's oceans, and thus a blank spot on the map of marine studies. Shaped by dynamic currents and shifting water masses, it is a key region in discussions about marine ecology, biodiversity, and zoogeography, while facing numerous, poorly understood, and unmonitored threats associated with climate change, acidification, and pollution. Polychaete diversity was assessed along four transects along the Ghana coast, from shallow to deep bottoms and distributed along the whole upwelling marine ecoregion. Despite high sampling effort, steep species accumulation curves demonstrated the necessity of further sampling in the region. We observed zonation of fauna by depth, and a decrease in species richness from 25 m to 1000 m depth. Polychaete communities were influenced by sediment type, presence of oxygen minimum zones, and local disturbances caused by elevated barium concentrations. Similar evenness along the depth gradient reflected the importance of rare species in the community structure. Differences in phylogenetic diversity, as reflected by taxonomic distinctness, were small, which suggested high ecosystem stability. The highly variable species richness at small scale (meters) showed the importance of ecological factors giving rise to microhabitat diversity, although we also noticed intermediate scale (50-300 km) differences affecting community structure. About 44 % of the species were rare (i.e. recorded only in three or fewer samples), highlighting the level of patchiness, while one fifth was distributed on all transects, therefore along the whole upwelling ecoregion, demonstrating the influence of the regional species pool on local communities at particular stations. Our study yielded 253 species, increasing the number of polychaetes known from this region by at least 50 %. This casts doubt on previous findings regarding Atlantic bioregionalization, biodiversity estimates and endemism, which appear to have been more pronouncedly affected by sampling bias than previously thought.

Shallow- and Deep-Water Ophiura Species Produce a Panel of Chlorin Compounds with Potent Photodynamic Anticancer Activities

A Pacific brittle star Ophiura sarsii has previously been shown to produce a chlorin (3S,4S)-14-Ethyl-9-(hydroxymethyl)-4,8,13,18-tetramethyl-20-oxo-3-phorbinepropanoic acid (ETPA) (1) with potent phototoxic activities, making it applicable to photodynamic therapy. Using extensive LC-MS metabolite profiling, molecular network analysis, and targeted isolation with de novo NMR structure elucidation, we herein identify five additional chlorin compounds from O. sarsii and its deep-sea relative O. ooplax: 10S-Hydroxypheophorbide a (2), Pheophorbide a (3), Pyropheophorbide a (4), (3S,4S,21R)-14-Ethyl-9-(hydroxymethyl)-21-(methoxycarbonyl)-4,8,13,18-tetramethyl-20-oxo-3-phorbinepropanoic acid (5), and (3S,4S,21R)-14-Ethyl-21-hydroxy-9-(hydroxymethyl)-4,8,13,18-tetramethyl-20-oxo-3-phorbinepropanoic acid (6). Chlorins 5 and 6 have not been previously reported in natural sources. Interestingly, low amounts of chlorins 1-4 and 6 could also be identified in a distant species, the basket star Gorgonocephalus cf. eucnemis, demonstrating that chlorins are produced by a wide spectrum of marine invertebrates of the class Ophiuroidea. Following the purification of these major Ophiura chlorin metabolites, we discovered the significant singlet oxygen quantum yield upon their photoinduction and the resulting phototoxicity against triple-negative breast cancer BT-20 cells. These studies identify an arsenal of brittle star chlorins as natural photosensitizers with potential photodynamic therapy applications.

The added costs of winter ocean warming for metabolism, arm regeneration and survival in the brittle star Ophionereis schayeri

As the climate continues to change, it is not just the magnitude of these changes that is important - equally critical is the timing of these events. Conditions that may be well tolerated at one time can become detrimental if experienced at another, as a result of seasonal acclimation. Temperature is the most critical variable as it affects most aspects of an organism's physiology. To address this, we quantified arm regeneration and respiration in the Australian brittle star Ophionereis schayeri for 10 weeks in response to a +3°C warming (18.5°C, simulating a winter heatwave) compared with ambient winter temperature (15.5°C). The metabolic scaling rate (b=0.635 at 15.5°C and 0.746 at 18.5°C) with respect to size was similar to that of other echinoderms and was not affected by temperature. Elevated temperature resulted in up to a 3-fold increase in respiration and a doubling of regeneration growth; however, mortality was greater (up to 44.2% at 18.5°C), especially in the regenerating brittle stars. Metabolic rate of the brittle stars held at 18.5°C was much higher than expected (Q10≈23) and similar to that of O. schayeri tested in summer, which was near their estimated thermotolerance limits. The additional costs associated with the elevated metabolism and regeneration rates incurred by the unseasonably warm winter temperatures may lead to increased mortality and predation risk.

Worms and gills, plates and spines: the evolutionary origins and incredible disparity of deuterostomes revealed by fossils, genes, and development

Deuterostomes are the major division of animal life which includes sea stars, acorn worms, and humans, among a wide variety of ecologically and morphologically disparate taxa. However, their early evolution is poorly understood, due in part to their disparity, which makes identifying commonalities difficult, as well as their relatively poor early fossil record. Here, we review the available morphological, palaeontological, developmental, and molecular data to establish a framework for exploring the origins of this important and enigmatic group. Recent fossil discoveries strongly support a vermiform ancestor to the group Hemichordata, and a fusiform active swimmer as ancestor to Chordata. The diverse and anatomically bewildering variety of forms among the early echinoderms show evidence of both bilateral and radial symmetry. We consider four characteristics most critical for understanding the form and function of the last common ancestor to Deuterostomia: Hox gene expression patterns, larval morphology, the capacity for biomineralization, and the morphology of the pharyngeal region. We posit a deuterostome last common ancestor with a similar antero-posterior gene regulatory system to that found in modern acorn worms and cephalochordates, a simple planktonic larval form, which was later elaborated in the ambulacrarian lineage, the ability to secrete calcium minerals in a limited fashion, and a pharyngeal respiratory region composed of simple pores. This animal was likely to be motile in adult form, as opposed to the sessile origins that have been historically suggested. Recent debates regarding deuterostome monophyly as well as the wide array of deuterostome-affiliated problematica further suggest the possibility that those features were not only present in the last common ancestor of Deuterostomia, but potentially in the ur-bilaterian. The morphology and development of the early deuterostomes, therefore, underpin some of the most significant questions in the study of metazoan evolution.

Embryotoxicity and Teratogenicity of Steroidal Saponin Isolated from Ophiopholis mirabilis

Benthic invertebrates produce secondary metabolites that serve as defenses against consumers and promote their fitness. To explore the chemical defense in marine benthic echinoderms, the chemical constituents of Ophiopholis mirabilis were investigated. A steroidal monoglycoside, asterosaponin P1, was isolated from O. mirabilis for the first-time using column chromatography. The chemical structure was characterized by spectroscopic and spectrometric methods. The embryotoxicity and teratogenicity of the isolated compound were assessed using the zebrafish embryo assay, a powerful vertebrate animal model system to study mechanisms of toxicity. When applied at high concentrations, asterosaponin P1 causes a significant increase in embryo mortality. A moderate LC₅₀ of asterosaponin P1 appeared to be time- and concentration-dependent in its toxicity to zebrafish embryos. Teratogenicity in zebrafish embryos also included morphological defects, decreased hatchability, and a reduced heart rate. These findings revealed that steroidal saponin extracted from O. mirabilis exhibited acute toxic effects on zebrafish embryos, suggesting a potential chemical defense function in marine habitats.

A Sister-Group Comparison of Branching and Pedicellariae in Brittlestars (Echinodermata: Ophiuroidea)

Branching of arms and presence of pedicellariae are characters among ophiuroids found only in the order Euryalida (snakestars and basketstars). Family Asteronychidae has neither character; family Euryalidae has 2 small clades with branched arms; and family Gorgonocephalidae has all species with pedicellariae and 3 or 4 clades with branched arms. Despite the rare occurrence of these characters in the Ophiuroidea, they might be key adaptations within the Euryalida that have led to relatively high diversification. Sister-group comparison of the distribution of these 2 characters among taxa indicates that neither character alone explains diversity patterns within the order. In particular, branching restricted to the tips of arms seems not strongly adaptive, probably for the lack of integration of basal forks with the disc. On the other hand, 2 clades of gorgonocephalids with basal branching exceed their snakestar sister groups in numbers of species, indicating an advantage of branching within the family. Unfortunately, the analysis cannot benefit from statistics, for at least 5 independent comparisons are required for a one-tailed sign test. Because branching and pedicellariae are probably not independent variables, future sister-group comparisons should be done only within the Gorgonocephalidae once clade structure is better clarified with increased taxon sampling (10 currently missing genera) and resolution of intra-generic inconsistencies in the most recent cladograms available. Branching might confer upon gorgonocephalid basketstars a more efficient use of pedicellariae for upstream capture of zooplankton over their snakestar relatives as well as over the Euryalidae, which retain ancestral downstream capture by mucus-laden podia.

Fatty Acids of Echinoderms: Diversity, Current Applications and Future Opportunities

The phylum Echinodermata comprising the classes Asteroidea, Ophiuroidea, Echinoidea, Holothuroidea, and Crinodeia, is one of the important invertebrate groups. Members of this phylum live exclusively in marine habitats and are distributed in almost all depths and latitudes. Some of them, such as sea urchins and sea cucumbers, are commercially valuable and constitute a major fishery resource. Echinoderms are increasingly recognized as a unique source of various metabolites with a wide range of biological activities. The importance of dietary polyunsaturated fatty acids, such as eicosapentaenoic acid, in human health has drawn attention to echinoderms as a promising source of essential fatty acids (FAs). Extensive information on the FAs of the phylum has been accumulated to date. The biosynthetic capabilities and feeding habits of echinoderms explain the findings of the unusual FAs in them. Certain common and unusual FAs may serve as chemotaxonomic markers of the classes. The main goal of the review was to gather the relevant information on the distribution of FAs among the echinoderm classes, describe the structures, distribution, biosynthetic pathways, and bioactivity, with an emphasis on the FAs specific for echinoderms. A large part of the review is devoted to the FAs derived from echinoderms that exhibit various biological activities promising for potential therapeutic applications.

Intertidal Ophiuroidea from the Saurashtra coastline, Gujarat, India

Present communication reports the diversity of intertidal Ophiuroidea (Phylum: Echinodermata) from the intertidal zones of the Saurashtra coastline, Gujarat state. Saurashtra coastlines were extensively surveyed from January 2019 to March 2022 for the Ophiuroidea diversity. A total of nine species of Ophiuroidea belonging to eight genera and six families were noted from the intertidal zones of the Saurashtra coastline. Amongst these, Macrophiothrix variabilis, Ophiothrix savignyi and Ophiomaza cacaotica are newly observed species from the Gujarat coastline. The results of similarity indices show that each sampling site has a diverse variety of brittle star, making them spatially different from each other.

DNA barcoding echinoderms from the East Coast of South Africa. The challenge to maintain DNA data connected with taxonomy

Echinoderms are marine water invertebrates that are represented by more than 7000 extant species, grouped in five classes and showing diverse morphologies (starfish, sea lilies, feather stars, sea urchins, sea cucumbers, brittle and basket stars). In an effort to further study their diversity, DNA barcodes (DNA fragments of the 5' end of the cytochrome c oxidase subunit I gene, COI) have been used to complement morphological examination in identifying evolutionary lineages. Although divergent clusters of COI sequences were reported to generally match morphological species delineations, they also revealed some discrepancies, suggesting overlooked species, ecophenotypic variation or multiple COI lineages within one species. Here, we sequenced COI fragments of 312 shallow-water echinoderms of the East Coast of South Africa (KwaZulu-Natal Province) and compared morphological identifications with species delimitations obtained with four methods that are exclusively based on COI sequences. We identified a total of 103 morphospecies including 18 that did not exactly match described species. We also report 46 COI sequences that showed large divergences (>5% p-distances) with those available to date and publish the first COI sequences for 30 species. Our analyses also identified discordances between morphological identifications and COI-based species delimitations for a considerable proportion of the morphospecies studied here (49/103). For most of them, further investigation is necessary to keep a sound connection between taxonomy and the growing importance of DNA-based research.

Description of two species of the genus Astrodia Verrill, 1899 (Ophiuroidea, Euryalida, Asteronychidae), including a new species from seamounts in the West Pacific

Five specimens of Ophiuroidea from deep-sea seamounts in the West Pacific were collected and identified as two species, Astrodiaduospina sp. nov. and Astrodiaabyssicola. The new species, Astrodiaduospina sp. nov., can be distinguished from its congeners by having indistinct or underdeveloped oral papillae, relatively short genital slits, crescent-shaped lateral arm plates, and plate-shaped external ossicles on the aboral surface of the disc. One specimen was identified as Astrodiaabyssicola, which has been reported in the north-western Pacific and the north-eastern coast of Japan. The most recent tabular key of Astrodia was revised with two more key characteristics added, the shape and presence of oral papillae and the number of arm spines. The phylogenetic relationship of Astrodia and Asteronyx was analyzed based on 16S and COI sequences. The discovery of the two species further expanded the geographical distribution of the genus Astrodia.

Purification, characterization and cDNA cloning of a lectin from the brittle star Ophioplocus japonicus

Lectins are carbohydrate-binding proteins that possess specific sugar-binding properties and are involved in various biological activities in different organisms. In this study, purification, characterization, and cDNA cloning of a brittle star lectin, designated as Ophioplocus japonicus agglutinin (OJA), were conducted. OJA was isolated from the brittle star O. japonicus by affinity chromatography on a Sephadex G-25 column, followed by ion-exchange chromatography on a Resource Q column. This lectin yielded distinct bands at approximately 176 or 17 kDa on sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) under non-reducing or reducing conditions, respectively. It also exhibited Ca²⁺-dependent hemagglutination activity, which, however, was not affected by other metal cations, such as Ba²⁺, Co²⁺, Cu²⁺, Zn²⁺, Fe²⁺, Mg²⁺, and Mn²⁺. The OJA activity was strongly inhibited by glucose and xylose among the monosaccharides tested, and by bovine thyroglobulin among the glycoproteins tested. Cloning of the OJA cDNA revealed that its primary structure contained the C-type lectin domain (CTLD). The results of this study showed that OJA is an echinoderm-derived glucose/xylose-specific lectin that belongs to the C-type lectin superfamily.

Cytotoxic and antimicrobial activities of two new sesquiterpenoids from red sea brittle star Ophiocoma dentata

Bioactive compounds were extracted from a locally available brittle star; Ophiocoma dentata, collected from the Red Sea, Egypt. Two new sesquiterpenoids; 8, 11-epoxy-9(15)-himachaladiene-4-ol (O8-ophiocomane) and, 11-epoxy-9(15)-himachaladiene-4-ol (O7-ophiocomane) were isolated and characterized using appropriate techniques. Structure elucidation was estimated via 1D NMR, 2D NMR, FT-IR and mass spectroscopy analyses. The isolated compounds were tested for cytotoxic, antibacterial and antifungal activities. Pure compounds showed a dose dependent reduction in MCF-7 cells viability with LC50 of 103.5 and 59.5 μg/ml for compounds 1 and 2 respectively compared to the chemotherapeutic drug cisplatin (47.4 µg/ml). In vivo experiments showed that O. dentate extract significantly reduced tumor progression and improved hematological parameters and liver functions of tumor-bearing mice when administered either before or after tumor cells' injection. The most remarkable antimicrobial effects of O. dentate crude extract were against Staphylococcus aureus, Vibrio damsela and Pseudomonas aeruginosa while the pure compounds showed activity against P. aeruginosa alone. Neither the crude extract nor the pure compounds have shown activity against Aeromonas hydrophila. These results indicates that O. dentata extract and newly isolated compounds have shown a promising cytotoxic, antiproliferative and antimicrobial activities that might be useful for pharmaceutical applications.

The complete mitochondrial genome of Asteroschema tubiferum (Ophiuroidea: Euryalida: Asteroschematidae)

We describe the first mitochondrial genome of a brittle star Asteroschema tubiferum Matsumoto 1911 in family Asteroschematidae. The mitogenome was sequenced and assembled using next-generation sequencing technology, and were 16,361 bp in size with 37 genes containing 13 protein-coding genes, 22 tRNA genes, 2 rRNA genes, and a control region. The phylogenetic tree was constructed based on 13 protein-coding mitochondrial genes of A. tubiferum and 26 species in the phylum Echinodermata by RAxML, which showed that it was mostly related to the species in Family Gorgonocephalidae. These results could provide a novel insight to the phylogeny of Ophiuroidea.

Order Euryalida (Echinodermata, Ophiuroidea), new species and new records from the South China Sea and the Northwest Pacific seamounts

Ophiuroids were collected by the manned submersible ‘Shenhaiyongshi’ from the deep-sea seamounts in the South China Sea and Northwest Pacific regions at 602–1920 m depth, during 2018 to 2020. A total of nine species was identified, including two new species and seven new records from the South China Sea and one new record from the Northwest Pacific region. Two new species are described as Asteroschemashenhaiyongshiisp. nov. and Asteroschemadomogranulatumsp. nov. The seven new records included five species from the genus Asteroschema, and one species each from the genera Asterostegus and Astrodendrum. Comprehensive descriptions of morphological features are provided, including characteristics of the arm skeleton, as well as a phylogenetic analysis based on 16S and COI sequences. Intraspecific genetic distance ranges of Euryalida species from the present study were 0.34% to 1.38%, which was relatively low compared to other orders in the class Ophiuroidea. The present study suggests a high probability that species of the order Euryalida are more widely spread around the Indo-Pacific region than previously expected.

Mitochondrial phylogeny of the brittle star genus Ophioderma

We reconstructed the mitochondrial phylogeny of the species of the brittle star genus Ophioderma, using sequences of the Cytochrome Oxidase I gene (COI) to address four questions: (i) Are the species of Ophioderma described on morphological evidence reflected in mitochondrial genealogy? (ii) Which species separated from which? (iii) When did speciation events occur? (iv) What is the rate of COI evolution in ophiuroids? We found that most of the 22 described species we sampled coincide with monophyletic clusters of COI sequences, but there are exceptions, most notably in the eastern Pacific, in which three undescribed species were indicated. The COI phylogeny lacks resolution in the deeper nodes, but it does show that there are four species pairs, the members of which are found on either side of the central American Isthmus. Two pairs with a genetic distance of ~ 4% between Atlantic and Pacific members were probably split during the final stages of Isthmus completion roughly 3 million years ago. The rate of divergence provided by these pairs allowed the calibration of a relaxed molecular clock. Estimated dates of divergence indicate that the lineages leading to extant species coalesce at times much older than congeneric species in other classes of echinoderms, suggesting that low extinction rates may be one of the reasons that ophiuroids are species-rich. The mean rate of COI substitution in Ophioderma is three times slower than that of echinoids. Conclusions of previous mitochondrial DNA studies of ophiuroids that relied on echinoid calibrations to determine divergence times need to be revised.

Miniaturization during a Silurian environmental crisis generated the modern brittle star body plan

Pivotal anatomical innovations often seem to appear by chance when viewed through the lens of the fossil record. As a consequence, specific driving forces behind the origination of major organismal clades generally remain speculative. Here, we present a rare exception to this axiom by constraining the appearance of a diverse animal group (the living Ophiuroidea) to a single speciation event rather than hypothetical ancestors. Fossils belonging to a new pair of temporally consecutive species of brittle stars (Ophiopetagno paicei gen. et sp. nov. and Muldaster haakei gen. et sp. nov.) from the Silurian (444-419 Mya) of Sweden reveal a process of miniaturization that temporally coincides with a global extinction and environmental perturbation known as the Mulde Event. The reduction in size from O. paicei to M. haakei forced a structural simplification of the ophiuroid skeleton through ontogenetic retention of juvenile traits, thereby generating the modern brittle star bauplan.

Morphometry and Relative Growth of Ophiolepis crassa (Echinodermata: Ophiuroidea), a Brittle Star from the Eastern Pacific

Tropical ophiuroid fauna belonging to the family Ophiolepididae are almost unknown. This study deals with the relative growth and morphometric traits of the ophiuroid Ophiolepis crassa from the Gulf of California, Mexico. Specimens examined in this study came from the Colección Nacional de Equinodermos, Universidad Nacional Autónoma de México, and were collected over soft bottoms off Punta Gorda. Thirteen anatomical features were measured in a total of 152 specimens, including disk diameter, arm length, as well as length and width of dorsal and ventral arm plates, and radial, oral, and adoral shields. Based on the range of values of the disk diameter, varying from 4 to 19 mm, we provided quantitative data on each anatomical measurement considering three size classes. Morphometric data were adjusted to a power equation to detect the degree of allometry in the growth of anatomical traits. Results indicated that all the ventral and dorsal plates, as well as the radial, oral, and adoral shields, suffer changes in shape during growth, but these changes are stronger in the plates. In addition, an analysis of symmetry applied to both right and left radial shields revealed that these structures remain nearly symmetrical during growth. The disk diameter vs arm/disk relationship indicated that the species is a surface dweller inhabitant of the seafloor. This study, based on a single sample collected in a restricted area of the eastern Pacific, provides useful quantitative information for further taxonomic, systematic, or biogeographic studies.

A morphological and morphometric approach to study Ophiuroidea (Echinodermata): Size changes of Ophiocomella alexandri

Studies on size changes of Ophiuroidea are limited, despite their importance and implications in taxonomy, phylogenetics, ecology, and distribution. These studies have traditionally been based on descriptive size series seldom integrating quantitative analyses to assess the morphological variability of species, despite their potential use to study size changes in brittle stars. To confirm the latter, size changes of Ophiocomella alexandri were studied here using this approach. The studied size series of O. alexandri included specimens from 1.64 to 23.64 mm disc diameter (DD). Quantitative and qualitative external morphological characters were examined on each specimen, and quantitative analyses (cluster, one-way permutational analysis of variance, and discriminant analysis) were employed to identify size groups within the species. The allometric relationship disc diameter-total arm length (DD-AL) was estimated for each size group and the combined size groups. Two size groups were identified: Group 1, subdivided into Subgroup 1.1 and Subgroup 1.2, and Group 2. Each size group presented particular characters which were described, discussed, and compared with relevant literature. The relationship DD-AL was positively allometric for Group 1 and combined size groups, and isometric for Group 2. The results highlight the potential of quantitative analyses to address size-related morphological changes in ophiuroids, and the importance of conducting this type of study to correctly identify species regardless of their size. This is the first study to describe size-related morphological changes of a brittle star from the Eastern Pacific, and the first one focused on a member of Ophiocomidae globally.

Biodiversity of coral reef cryptobiota shuffles but does not decline under the combined stressors of ocean warming and acidification

Ocean-warming and acidification are predicted to reduce coral reef biodiversity, but the combined effects of these stressors on overall biodiversity are largely unmeasured. Here, we examined the individual and combined effects of elevated temperature (+2 °C) and reduced pH (-0.2 units) on the biodiversity of coral reef communities that developed on standardized sampling units over a 2-y mesocosm experiment. Biodiversity and species composition were measured using amplicon sequencing libraries targeting the cytochrome oxidase I (COI) barcoding gene. Ocean-warming significantly increased species richness relative to present-day control conditions, whereas acidification significantly reduced richness. Contrary to expectations, species richness in the combined future ocean treatment with both warming and acidification was not significantly different from the present-day control treatment. Rather than the predicted collapse of biodiversity under the dual stressors, we find significant changes in the relative abundance but not in the occurrence of species, resulting in a shuffling of coral reef community structure among the highly species-rich cryptobenthic community. The ultimate outcome of altered community structure for coral reef ecosystems will depend on species-specific ecological functions and community interactions. Given that most species on coral reefs are members of the understudied cryptobenthos, holistic research on reef communities is needed to accurately predict diversity-function relationships and ecosystem responses to future climate conditions.

Description of a New Brooding Species of Ophiodelos (Echinodermata: Ophiuroidea) from Japan

A new species of brittle star, Ophiodelos okayoshitakai, is described from two specimens collected in Sagami Bay, central-eastern Japan. Photographic examination of the holotype specimen of the sole other congener, Ophiodelos insignis Koehler, 1930, indicates that Ophiodelos okayoshitakai sp. nov. is distinguished from O. insignis by i) the disc stumps covering on the dorsal side of the disc, ii) the dorsal and ventral arm plates being separated from each other on the proximal arm regions, iii) the dorsal arm plate being smooth, iv) the arm spines at proximal portion of the arm being six in number and smooth in shape, and v) the number and shape of the tentacle scales at proximal portion of the arm being up to two and spine-shaped adradially and oval abradially. Detailed morphological observations of this new species suggest the inclusion of Ophiodelos, whose familial affiliation remains unclear, in the suborder Ophiacanthina. More than 10 juveniles of various sizes were found in the disc of Ophiodelos okayoshitakai sp. nov., indicating a brooding reproduction. This is the first report of the genus Ophiodelos from Japanese waters. We also provided a nucleotide sequence for part of the cytochrome c oxidase subunit I (COI) gene in O. okayoshitakai sp. nov. for future studies of DNA barcoding and phylogeny.

New fossils of Jurassic ophiurid brittle stars (Ophiuroidea; Ophiurida) provide evidence for early clade evolution in the deep sea

Understanding of the evolutionary history of the ophiuroids, or brittle stars, is hampered by a patchy knowledge of the fossil record. Especially, the stem members of the living clades are poorly known, resulting in blurry concepts of the early clade evolution and imprecise estimates of divergence ages. Here, we describe new ophiuroid fossil from the Lower Jurassic of France, Luxembourg and Austria and introduce the new taxa Ophiogojira labadiei gen. et sp. nov. from lower Pliensbachian shallow sublittoral deposits, Ophiogojira andreui gen. et sp. nov. from lower Toarcian shallow sublittoral deposits and Ophioduplantiera noctiluca gen. et sp. nov. from late Sinemurian to lower Pliensbachian bathyal deposits. A Bayesian morphological phylogenetic analysis shows that Ophiogojira holds a basal position within the order Ophiurida, whereas Ophioduplantiera has a more crownward position within the ophiurid family Ophiuridae. The position of Ophioduplantiera in the evolutionary tree suggests that family-level divergences within the Ophiurida must have occurred before the late Sinemurian, and that ancient slope environments played an important role in fostering early clade evolution.

Description of three species of ophioplinthacids, including a new species, from a deep seamount in the Northwest Pacific Ocean

Five specimens of brittle star were collected from a deep-sea seamount in the Northwest Pacific, and identified into three species. One which is new to science, Ophioplinthaca grandisquama n. sp., can be easily distinguished from its congeners by the distinctly elongated and stout tentacle scales, stout and long disc spines, capitate with typically elongate to flaring head bearing numerous distinct thorns, radial shields roughly triangular and contiguous distally. One specimen was identified as Ophioplinthaca semele (Clark, 1949), which had been reported in Hawaii seamounts, is a new record of this species in the Northwest Pacific. The remaining specimen was an unknown species of Ophioplinthaca, with some different characteristics from other species of Ophioplinthaca. However, we, herein, prefer not to attach a name to this specimen until more morphological characteristics are available. The finding of this new species and two new records further enriches the distribution of Ophioplinthaca in the seamount of Northwest Pacific, providing useful information for marine protection in the cobalt-rich area.

Three-dimensional visualization as a tool for interpreting locomotion strategies in ophiuroids from the Devonian Hunsrück Slate

Living brittle stars (Echinodermata: Ophiuroidea) employ a very different locomotion strategy to that of any other metazoan: five or more arms coordinate powerful strides for rapid movement across the ocean floor. This mode of locomotion is reliant on the unique morphology and arrangement of multifaceted skeletal elements and associated muscles and other soft tissues. The skeleton of many Palaeozoic ophiuroids differs markedly from that in living forms, making it difficult to infer their mode of locomotion and, therefore, to resolve the evolutionary history of locomotion in the group. Here, we present three-dimensional digital renderings of specimens of six ophiuroid taxa from the Lower Devonian Hunsrück Slate: four displaying the arm structure typical of Palaeozoic taxa (Encrinaster roemeri, Euzonosoma tischbeinianum, Loriolaster mirabilis, Cheiropteraster giganteus) and two (Furcaster palaeozoicus, Ophiurina lymani) with morphologies more similar to those in living forms. The use of three-dimensional digital visualization allows the structure of the arms of specimens of these taxa to be visualized in situ in the round, to our knowledge for the first time. The lack of joint interfaces necessary for musculoskeletally-driven locomotion supports the interpretation that taxa with offset ambulacrals would not be able to conduct this form of locomotion, and probably used podial walking. This approach promises new insights into the phylogeny, functional morphology and ecological role of Palaeozoic brittle stars.

Morphogenesis and histogenesis during the arm regeneration in a basket star Astrocladus dofleini (Euryalida, Ophiuroidea, Echinodermata)

Basket stars, that is, Ophiuroidea in Echinodermata, exhibit distinctive morphological characteristics with their complicatedly branched arms that can regenerate immediately after mutilation. Although, in brittle stars, that is, ophiuroids with nonbranched arms, the arm regeneration process following accidental trauma or autotomy have been morphologically and histologically observed in several species, few studies have so far been carried out on the regeneration of branched arms in basket stars. In this study, the developmental and morphological features of arm regeneration in Astrocladus dofleini (Gorgonocephalidae, Euryalida, Euryophiurida), one of the most common basket star species in Japanese waters, was anatomically and histologically investigated. Results clearly showed the following phases during the arm regeneration: (a) repair phase, (b) early regenerative phase, (c) intermediate regenerative phase, (d) advanced regenerative Phase I, and (e) advanced regenerative Phase II. The morphogenetic process during the arm regeneration in the basket star showed similar patterns to those of nonbranched arms observed in other ophiuroids. However, differences were also seen between the two ophiuroid types, that is, there were some developmental features specific to the basket star. In the early regenerative phase, branching of coelomic cavities was observed prior to the formation of other tissues, probably inducing the later morphogenesis of branched arms. In addition, hard skeletal ossicles form rapidly at the advanced regenerative Phase II. These developmental features may have led the evolution of bizarre morphologies seen in basket stars, probably contributing to the adaptation to shallow waters from deep-sea habitats.

Convergent Evolution and Structural Adaptation to the Deep Ocean in the Protein-Folding Chaperonin CCTα

The deep ocean is the largest biome on Earth and yet it is among the least studied environments of our planet. Life at great depths requires several specific adaptations; however, their molecular mechanisms remain understudied. We examined patterns of positive selection in 416 genes from four brittle star (Ophiuroidea) families displaying replicated events of deep-sea colonization (288 individuals from 216 species). We found consistent signatures of molecular convergence in functions related to protein biogenesis, including protein folding and translation. Five genes were recurrently positively selected, including chaperonin-containing TCP-1 subunit α (CCTα), which is essential for protein folding. Molecular convergence was detected at the functional and gene levels but not at the amino-acid level. Pressure-adapted proteins are expected to display higher stability to counteract the effects of denaturation. We thus examined in silico local protein stability of CCTα across the ophiuroid tree of life (967 individuals from 725 species) in a phylogenetically corrected context and found that deep-sea-adapted proteins display higher stability within and next to the substrate-binding region, which was confirmed by in silico global protein stability analyses. This suggests that CCTα displays not only structural but also functional adaptations to deep-water conditions. The CCT complex is involved in the folding of ∼10% of newly synthesized proteins and has previously been categorized as a "cold-shock" protein in numerous eukaryotes. We thus propose that adaptation mechanisms to cold and deep-sea environments may be linked and highlight that efficient protein biogenesis, including protein folding and translation, is a key metabolic deep-sea adaptation.

A taxonomic review of the genus Astrocladus (Echinodermata, Ophiuroidea, Euryalida, Gorgonocephalidae) from Japanese coastal waters

Japanese species of the genus Astrocladus (Echinodermata, Ophiuroidea, Euryalida, Gorgonocephalidae) are reviewed. Astrocladus coniferus recently has two junior synonyms, A. dofleini Döderlein and A. pardalis Döderlein, however, status of these species has long been questioned. These species concepts have not been reviewed in recent years and no molecular phylogenetic analyses have been performed. Observations of the lectotype of A. coniferus, as well as the lectotype and four paralectotypes of A. dofleini and the holotype of A. pardalis have revealed that A. coniferus and A. pardalis are conspecific and morphologically distinguishable from A. dofleini. Astrocladus coniferus and A. dofleini are supported as distinct species by our molecular data. Additionally, we re-describe A. exiguus and A. annulatus, based on recently collected specimens and the holotype. We conclude that four species, A. annulatus, A. coniferus, A. dofleini, and A. exiguus are present in Japanese waters.

A new ophiacanthid brittle star (Echinodermata, Ophiuroidea) from sublittoral crinoid and seagrass communities of late Maastrichtian age in the southeast Netherlands

A new species of brittle star, Ophiomitrella floorae, is recorded from the lower two meters of the Gronsveld Member (Maastricht Formation), of late Maastrichtian age (c. 66.7 Ma). These relatively fine-grained biocalcarenites reflect shallow-water deposition in a sheltered setting with a relatively firm sea floor and clear waters, under middle sublittoral and subtropical conditions. Associated echinoderm taxa comprise more robust, sturdy-plated ophiomusaid and ophiodermatid brittle stars and numerous bourgueticrinine sea lilies. The new brittle star described herein belongs to a family whose present-day members are predominantly restricted to bathyal depths. Its small size and the exceptional preservation of a single articulated specimen partially wrapped around the stalk of a bourgueticrinine suggest that O. floorae n. sp. was probably epizoic and specifically associated with stalked crinoids.

Gorgonocephalus eucnemis (Echinodermata: Ophiuroidea) and Bursal Ventilation

The basket star Gorgonocephalus eucnemis is an aerobic organism highly dependent on dissolved oxygen in surrounding waters. Previous observations on the anatomy of Gorgonocephalus state that five pairs of ossicles (the radial shields and genital plates) regulate the position of the roof of the body disc and are responsible for flushing seawater into and out of the bursae, though this seems never to have been empirically tested. In the current study, rates of bursal ventilation were investigated in response to an increase in the availability of food and, separately, exposure to hypoxic levels of dissolved oxygen. When fed with suspended krill particles, basket stars increased rates of bursal ventilation, ranging from 13% to 155%, resulting in a similar increase in volume of water moved in and out of bursae. This rate remained elevated for an average of 25 minutes after active feeding ended. Bursal ventilation rates also increased significantly (~60% average increase) when basket stars were exposed to hypoxic conditions (dissolved oxygen ≤ 3.5 mg O₂ L^-1 = 2.45 mL O₂ L^-1). Some specimens exhibited a loss of coordination in hypoxic conditions. All specimens recovered and resumed a normal rate of bursal ventilation when returned to normoxic conditions. Measurements show that dissolved oxygen levels decreased from outside to inside bursae and suggest that dissolved oxygen is absorbed in bursae during bursal ventilations. Increasing rates of bursal ventilation may help meet the increased oxygen demands when feeding and may help animals endure some exposures to hypoxia.

Microplastic pollution in deep-sea sediments and organisms of the Western Pacific Ocean

Microplastics are ubiquitous in marine environments. Sediments and marine organisms are recognized as the carriers and final destinations of microplastics. However, research on the concentration and abundance of microplastics in deep-sea sediments and organisms is limited. In this study, samples of sediments and organisms were collected from deep-sea locations of the western Pacific Ocean, with the depth ranging from 4601 m to 5732 m. Microplastics were extracted from the samples and analyzed by micro-Fourier-transform infrared spectroscopy. The average abundance of microplastics in the sediments was 240 items per kg dry weight of sediment. The microplastics were predominantly fibrous in shape (52.5%), blue in color (45.0%), and less than 1 mm in size (90.0%). The most commonly detected polymers were poly(propylene-ethylene) copolymer (40.0%) and polyethylene terephthalate (27.5%). The concentrations of polychlorinated biphenyls (PCBs), which are representatives of persistent organic pollutants, in the pore water of sediment samples were also investigated. A significant correlation between the distribution of microplastics and the PCB concentrations in sediments was found (P = 0.016). Microplastics were also detected in deep-sea organisms (i.e., Crinoidea, Pheronematidae, Ophiuroidea, and Gammaridea) in the sampling region, with an abundance of 0-3 items per individual biological sample. This assessment of microplastics in deep-sea sediments and benthic organisms of the western Pacific Ocean confirms that microplastic pollution exists in the deep-sea ecosystems of this region.

Troglomorphism in the brittle star Ophionereis commutabilis Bribiesca-Contreras et al., 2019 (Echinodermata, Ophiuroidea, Ophionereididae)

Due to their peculiar and sometimes bizarre morphology, cave fauna (across invertebrates and vertebrates from both aquatic and terrestrial cave habitats) have fascinated researchers throughout history. Despite their success in colonizing most marine ecosystems, the adaptations of cave brittle stars (Ophiuroidea) to a stygobiotic lifestyle have been scarcely examined. Employing comparative methods on a data set of two species belonging to the genus Ophionereis, this study addresses whether a cave-dwelling species from Cozumel exhibited similar troglomorphic traits as those of other taxa inhabiting caves. Our work demonstrated that some characters representing potential morphological cave adaptations in O. commutabilis were: bigger sizes, elongation of arms and tube feet and the presence of traits potentially paedomorphic. In addition, an element of ophiuroid’s photoreceptor system, as well as pigmentation, was observed to be peculiar in this stygobiotic species, plausibly as a result of inhabiting a low light-energy environment. Finally, we add evidence to the statement that O. commutabilis is a cave endemic species, already supported by demography, distribution and origin of this species, and now by a typical array of troglomorphisms.

The structural origins of brittle star arm kinematics: An integrated tomographic, additive manufacturing, and parametric modeling-based approach

Brittle stars are known for the high flexibility of their arms, a characteristic required for locomotion, food grasping, and for holding onto a great diversity of substrates. Their high agility is facilitated by the numerous discrete skeletal elements (ossicles) running through the center of each arm and embedded in the skin. While much has been learned regarding the structural diversity of these ossicles, which are important characters for taxonomic purposes, their impact on the arms' range of motion, by contrast, is poorly understood. In the present study, we set out to investigate how ossicle morphology and skeletal organization affect the flexibility of brittle star arms. Here, we present the results of an in-depth analysis of three brittle star species (Ophioplocus esmarki, Ophiopteris papillosa, and Ophiothrix spiculata), chosen for their different ranges of motion, as well as spine size and orientation. Using an integrated approach that combines behavioral studies with parametric modeling, additive manufacturing, micro-computed tomography, scanning electron microscopy, and finite element simulations, we present a high-throughput workflow that provides a fundamental understanding of 3D structure-kinematic relationships in brittle star skeletal systems.