Ophiuroids, as an important group of echinoderms, are widely distributed in marine benthic habitats. Previous studies have identified two primary feeding types of ophiuroids in the Yellow Sea, including carnivorous (Ophiura sarsii vadicola and Stegophiura sladeni) and suspension feeders (Ophiopholis mirabilis). Despite their ecological role in the benthic food webs, little is known about their accumulation of trace metal elements (TMEs). In this study, the content of TMEs (Pb, As, Cd, Hg, Cr, Cu, Zn), methylmercury (MeHg) and δ15N value of three ophiuroids species from the North Yellow Sea were determined. Our results showed that the contents of some TMEs (As, Cd, Cr, Cu and Zn) and MeHg were significantly different in three species of ophiuroid (p < 0.05). There were significant correlations between the accumulations of trace metal elements (Pb, Cd and Zn) and the δ15N value of the ophiuroids (p < 0.05). Additionally, As and Zn exhibited opposite correlations in ophiuroid with two feeding types, which may be related to their host species and different feeding habits. This study provided fundamental data for understanding the distribution of trace metal elements in echinoderms.

The Sox gene family, a collection of transcription factors widely distributed throughout the animal kingdom, plays a crucial role in numerous developmental processes. Echinoderms occupy a pivotal position in many research fields, such as neuroscience, sex determination and differentiation, and embryonic development. However, to date, no comprehensive study has been conducted to characterize and analyze Sox genes in echinoderms. In the present study, the evolution and expression of Sox family genes across 11 echinoderms were analyzed using bioinformatics methods. The results revealed a total of 70 Sox genes, with counts ranging from 5 to 8 across different echinoderms. Phylogenetic analysis revealed that the identified Sox genes could be categorized into seven distinct classes: the SoxB1 class, SoxB2 class, SoxC class, SoxD class, SoxE class, SoxF class and SoxH class. Notably, the SoxB1, SoxB2, and SoxF genes were ubiquitously present in all the echinoderms studied, which suggests that these genes may be conserved in echinoderms. The spatiotemporal expression patterns observed for Sox genes in the three echinoderms indicated that various Sox members perform distinct functional roles. Notably, SoxB1 is likely involved in echinoderm ovary development, while SoxH may play a crucial role in testis development in starfish and sea cucumber. In general, the present investigation provides a molecular foundation for exploring the Sox gene in echinoderms, providing a valuable resource for future phylogenetic and genomic studies.

The cold-water species Ophiura sarsii, a brittle star, is a key echinoderm in the Arctic continental shelf region, highly sensitive to climate change. However, the absence of a high-quality genome has hindered a thorough understanding of its adaptive evolution. In this study, we reported the first chromosome-level genome assembly of O. sarsii. The genome assembly totalled 1.57 Gb, encompassing 19 chromosomes with a GC content of 37.11% and a scaffold N50 length of 78.03 Mb. The Benchmarking Universal Single-Copy Orthologs (BUSCO) assessment yielded a completeness estimate of 93.5% for this assembly. We predicted a total of 27,099 protein-coding genes, with 25,079 functionally annotated. The genome was comprised of 58.09% transposable elements. This chromosome-level genome of O. sarsii contributes to our understanding of the origin and evolution of marine organisms.

Brisingida Fisher 1928 is one of the seven currently recognised starfish orders, and one of the least known taxa as being exclusive deep-sea inhabitants. Modern deep-sea expeditions revealed their common occurrences in various deep-sea settings including seamounts, basins and hydrothermal vent peripheral, underlining the necessity of clarifying their global diversity and phylogeny. In this study, we present a comprehensive molecular phylogeny of Brisingida which encompasses the highest taxonomic diversity to date. DNA sequences (COI, 16S, 12S and 28S) were obtained from 225 specimens collected in the global ocean, identified as 58 species spanning 15 of the 17 extant genera. Phylogenetic relationship was inferred using both maximum likelihood and Bayesian inference methods, revealing polyphyletic families and genera and indicating nonnegligible bias in prior morphology-based systematics. Based on the new phylogeny, a novel classification of the order, consisting of 5 families and 17 genera, is proposed. Families Odinellidae, Brisingasteridae and Novodiniidae (sensu Clark and Mah, 2001) were resurrected to encompass the genera Odinella, Brisingaster and Novodinia. Brisingidae and Freyellidae were revised to include 11 and 3 genera, respectively. A new genus and species, two new subgenera and seven new combinations are described and a key to each genus and family is provided. Transformations of morphological traits were evaluated under the present phylogenetic hypothesis. A series of paedomorphic characters were found in many genera and species, which led to a high degree of homoplasy across phylogenetically distant groups. Our results provide new insights in the phylogeny and ontogeny of the order, and highlight the necessity to evaluate character convergence under sound phylogenetic hypothesis.

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.

Echinoderms are a phylum of invertebrate deuterostomes, which contain echinoids, asteroids, holothuroids, crinoids, and ophiuroids. Echinoderms have special evolutionary position and unique characteristics, including pentamerous radial body structure, elaborate calcareous endoskeletons, and versatile water vascular system. Echinoderms exhibit extraordinarily diverse reproductive modes: asexual reproduction, sexual reproduction, sexual reversal, etc. Endocrine regulation plays important well-known roles in sex differentiation, gonadal development and maturation, gametogenesis, and reproductive behavior in vertebrates. However, the entire picture of reproductive endocrinology in echinoderms as an evolutionary model of the closest marine invertebrate relatives to chordates has not been revealed. Here, we reviewed previous and recent research progress on reproductive endocrinology in echinoderms, mainly including two sections: Sex steroids in echinoderms and neuropeptide regulation in echinoderm reproduction. This review introduces a variety of endocrine regulatory mechanisms in reproductive biology of echinoderms. It discusses the vertebrate-like sex steroids, putative steroidogenic pathway and metabolism, and reproduction-related neuropeptides. The review will provide a deeper understanding about endocrine regulatory mechanisms of gonadal development in lower deuterostomes and the application of endocrine control in economic echinoderm species in aquaculture.

Aestivation is considered to be one of the \"purest\" hypometabolic states in nature, as it involves aerobic dormancy that can be induced and sustained without complex factors. Animals that undergo aestivation to protect themselves from environmental stressors such as high temperatures, droughts, and food shortages. However, this shift in body metabolism presents new challenges for survival, including oxidative stress upon awakening from aestivation, accumulation of toxic metabolites, changes in energy sources, adjustments to immune status, muscle atrophy due to prolonged immobility, and degeneration of internal organs due to prolonged food deprivation. In this review, we summarize the physiological and metabolic strategies, key regulatory factors, and networks utilized by aestivating animals to address the aforementioned components of aestivation. Furthermore, we present a comprehensive overview of the advancements made in aestivation research across major species, including amphibians, fish, reptiles, annelids, mollusks, and echinoderms, categorized according to their respective evolutionary positions. This approach offers a distinct perspective for comparative analysis, facilitating an understanding of the shared traits and unique features of aestivation across different groups of organisms.

The pea crabs, superfamily Pinnotheroidea, are exceptional among brachyuran crabs in their diverse symbiotic associations involving both inquilinism and protective symbiosis. While this group presents a rare opportunity for evolutionary comparative study of host switching and morphological evolution in marine macroinvertebrates, previous phylogenetic studies have been focused on systematics. Here, we reconstructed the most extensive phylogeny of Pinnotheroidea based on two mitochondrial and six nuclear markers, with the aim of elucidating the host switching pathways and the correlation between symbiotic lifestyles and selected morphological adaptations. Ancestral state reconstruction of host association revealed a monophyletic origin of symbiosis in the form of inquilinism. Subsequent shifts in microhabitat preference for burrows or worm tubes, and the move to protective symbiosis, primarily in the switch to mollusc endosymbiosis, contributed to radiation in Pinnotheridae. Further parallel colonisations of echinoderms and tunicates occurred but did not lead to extensive diversification, except in the Clypeasterophilus + Dissodactylus lineage, which experienced a unique switch to echinoderm ectosymbiosis. The evolution of the third maxillipeds, carapace shape and ambulatory pereiopods suggests a rather strong coupling with the symbiotic lifestyle (whether inquilinism or protective symbiosis). Phenotypic diversity of these characters was higher among species engaged in protective symbiosis, with convergence in form (or function) among those sharing the same host affiliation. Species having different host affiliations or symbiotic lifestyles might also exhibit convergence in the form of the three morphological traits, suggesting a common adaptive value of the specialisations. Pinnotherid crabs overall exhibited a lower trait diversity than the also symbiotic palaemonid shrimps with comparable species diversity. This may plausibly be attributed to differences in potential for morphological modification to serve additional functions among the traits analysed in the two groups, the less frequent host switching and the less diverse host affiliations, and thus a less complicated evolutionary history in pinnotherids.

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.

To detect potential impacts of climate change on the distribution of common echinoderm species in the Yellow Sea (YS) and East China Sea (ECS), species distribution models (SDMs) were applied. Ensemble SDMs were constructed and were in good model performance for six of the eight selected common echinoderm species. Under future climate scenarios, the brittle stars Ophiopholis mirabilis, Amphioplus depressus and the sea cucumber Protankyra bidentata were projected to expand in the southwestern areas of the YS, the ECS, and the coastal areas of the YS and ECS, respectively; the brittle stars Stegophiura sladeni, Amphiura digitula and Amphiura vadicola will likely contract their ranges in the south distribution areas and expand in the north, showing a northward movement trend. Temperature was the most important environmental variable influencing the distribution of the latter three echinoderms. Our findings will improve our understanding of the impacts of climate change on marine species distributions.