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Simple Summary: Basement membranes (BMs) are thin sheets of connective tissue that form boundary layers in the organs of most animal bodies. There is increasing interest in how changes in the strength and stiffness of BMs contribute to the normal processes by which fertilized eggs become mature adults and the abnormal processes associated with disease, such as the spread of cancerous tumors. The spread of cancer can be helped by the weakening and disruption of BMs, which is thought to result mainly from BM components being broken down by specific enzymes, although other factors may be involved. Brittlestars are marine invertebrate animals related to starfish and sea urchins. The BMs of their muscles act as tendons that link the muscles to the skeleton. Brittlestars are able to jettison their arms when they are attacked by predators. Such arm loss depends partly on the ability of muscles to detach from the skeleton due to the sudden weakening of their tendons. This contribution provides an overview of current knowledge of the structure and mechanical behavior of BMs in non-echinoderm animals and of brittlestar tendons and discusses the possible usefulness of brittlestar tendons as a model for understanding mechanisms of BM weakening in normal and disease-related processes. Basement membranes (BMs) are thin layers of extracellular matrix that separate epithelia, endothelia, muscle cells, and nerve cells from adjacent interstitial connective tissue. BMs are ubiquitous in almost all multicellular animals, and their composition is highly conserved across the Metazoa. There is increasing interest in the mechanical functioning of BMs, including the involvement of altered BM stiffness in development and pathology, particularly cancer metastasis, which can be facilitated by BM destabilization. Such BM weakening has been assumed to occur primarily through enzymatic degradation by matrix metalloproteinases. However, emerging evidence indicates that non-enzymatic mechanisms may also contribute. In brittlestars (Echinodermata, Ophiuroidea), the tendons linking the musculature to the endoskeleton consist of extensions of muscle cell BMs. During the process of brittlestar autotomy, in which arms are detached for the purpose of self-defense, muscles break away from the endoskeleton as a consequence of the rapid destabilization and rupture of their BM-derived tendons. This contribution provides a broad overview of current knowledge of the structural organization and biomechanics of non-echinoderm BMs, compares this with the equivalent information on brittlestar tendons, and discusses the possible relationship between the weakening phenomena exhibited by BMs and brittlestar tendons, and the potential translational value of the latter as a model system of BM destabilization. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Brittle stars (Class Ophiuroidea), like all echinoderms, lack centralized nervous systems, having instead five radially arranged nerve cords joined by a central nerve ring. Although operant and classical conditioning have been demonstrated in a limited number of studies in sea stars (Class Asteroidea), members of the other echinoderm classes remain relatively untested. We examined whether individuals of the ophiuroid species Ophiocoma echinata were able to learn an association between a period of darkness and the presentation of a food reward. Ophiuroids in an experimental group were trained by presenting food during a 30-minute period of darkness, while control group animals were fed under regular daytime room lights many hours after a period of darkness of the same duration. After the training period, the experimental group demonstrated they had learned to associate the two cues by regularly emerging during the dark period even when no food was presented. The untrained control animals, as well as pre-training experimental animals, did not emerge during the dark periods when no food was presented. Once trained, experimental animals emerged significantly more times than control animals during dark periods without food (trained emergences = 109; untrained emergences = 22; χ2 = 64.65, p = 0.0007). This study shows that classical conditioning is possible in a class of animals that lacks a centralized nervous system. Significance Statement: Here we show that ophiuroids can learn to associate two stimuli (darkness and food) in the first investigation of classical conditioning in this class of animals in ~ 80 years. Previously, researchers have found only limited evidence for this type of learning in echinoderms. Like other echinoderms, ophiuroids lack a brain or centralized ganglion, possessing instead a decentralized nervous system made of five radial nerve cords joined by a central ring. Although there is growing interest in the mechanisms of locomotion and coordination in these animals, their potential for learning and memory remains essentially unexplored. Investigating learning and memory in ophiuroids has the potential to reveal more about neural processing in decentralized nervous systems as well as provide new avenues for understanding their behavioral ecology. [ABSTRACT FROM AUTHOR]

In spite of considerable progress during the last few years, the fossil record of the ophiuroids, or brittle stars, is still poorly known, especially with respect to taxa restricted to specific environments. Here, we describe new ophiuroid fossils collected from an Upper Cretaceous rocky shore in Ivö Klack, southern Sweden, consisting of fully disarticulated skeletal remains retrieved from the sediments deposited between boulders and hummocks. The fossils are identified as a new species of the extant ophiocomid genus Ophiocoma. In a critical revision of the ophiocomid fossil record, we show that all fossils previously assigned to the Ophiocomidae belong to other families. Thus, the fossil record of the Ophiocomidae is currently restricted to the new species described herein, and Amphiura? gigantiformis from the Miocene of Austria which, in fact, is a species of Ophiocoma. Since recent species of Ophiocoma exclusively occur in tropical to subtropical shallow subtidal environments, our discovery of a fossil Ophiocoma species in the rocky shore sediments of Ivö therefore conforms with the previously assumed subtropical palaeotemperatures prevailing in southern Sweden during the Late Cretaceous. Most notably, it represents the northernmost occurrence of an ophiocomid recorded to date. [ABSTRACT FROM AUTHOR]

Class Ophiuroidea groups the most diverse and abundant organisms of the phylum Echinodermata, having approximately 2100 described species. They have a simple body plan, consisting of a central disk, where their main internal organs are located, and to which the arms are attached. Species are identified based mostly on external morphological characters. However, many species present similar diagnostic characters in several families, which makes their phylogenetic reconstruction quite complex. Furthermore, many of these characters undergo changes during post-larval development and growth. Therefore, ontogenetic studies become relevant. Progress is still slow in this field, however, mainly due to difficulties in identifying some species in these stages. Despite significant advances in the number of species described for the Northeast region of Brazil, studies on the growth series of species of Ophiuroidea reported for this region are still scarce. The present work describes the intraspecific variations of Ophionereis reticulata (Say, 1825), Ophionereis squamulosa Koehler, 1914, and Amphipholis squamata (Delle Chiaje, 1828), considering young and adult specimens. The morphometry of individuals and aspects of microstructure are included. The description of morphological characters in growth series allowed us to identify typical characteristics of certain stages. Some structures remained almost unchanged, while others underwent most of the changes, being used to characterize different growth stages. Such stages are helpful for the correct identification of these species. In addition, the study of morphological variations between young and adult specimens contributes to our understanding on evolutionary relationships within Ophiuroidea. [ABSTRACT FROM AUTHOR]

Articulated fossil ophiuroids from South America were reported for the Devonian, Cretaceous, Eocene, and Miocene. Here we report the first Jurassic record of an articulated ophiuroid from the Sierra Chacaicó Formation (early Pliensbachian– Sinemurian) in Neuquén Basin, Argentina, and discuss the taphonomic processes that allowed its preservation. The Sierra Chacaicó Formation represents the onset of the Early Jurassic extensive marine transgression in the basin. The basal section comprises shoreface and offshore Gilbert-type delta system, which was affected by hyperpycnal discharges. The middle and upper sections are represented by offshore deposits, affected by storms and eroded by hyperpycnal channel-levee systems. The ophiuroid specimen was found in levels of massive, fine, tuffaceous sandstone beds and covered by coarse sandstone containing a large amount of plant debris and organic matter. It was preserved articulated, with a complete disc and almost complete arms. Based on the microstructure of the spine-bearing lateral arm plates, the ophiuroid is assigned to Sinosura, an extinct genus of the family Ophioleucidae, widespread in the Lower Jurassic deposits of Europe but previously unknown from other parts of the world. The posture of the ophiuroid, with one arm curved distally and extended in one direction and the other four arms symmetrically oriented in the opposite direction, suggests a walking or escape movement frozen in time. This implies that the ophiuroid was buried alive by sediment thick enough to prevent successful escape. The taphonomic and sedimentologic evidence indicates that the fossil material was found in hyperpycnal deposits accumulated in offshore positions, which carried a high concentration of sediment in suspension.

Abstract Background Echinoderms are established models in experimental and developmental biology, however genomic resources are still lacking for many species. Here, we present the draft genome of Ophioderma brevispinum, an emerging model organism in the field of regenerative biology. This new genomic resource provides a reference for experimental studies of regenerative mechanisms. Results We report a de novo nuclear genome assembly for the brittle star O. brevispinum and annotation facilitated by the transcriptome assembly. The final assembly is 2.68 Gb in length and contains 146,703 predicted protein-coding gene models. We also report a mitochondrial genome for this species, which is 15,831 bp in length, and contains 13 protein-coding, 22 tRNAs, and 2 rRNAs genes, respectively. In addition, 29 genes of the Notch signaling pathway are identified to illustrate the practical utility of the assembly for studies of regeneration. Conclusions The sequenced and annotated genome of O. brevispinum presented here provides the first such resource for an ophiuroid model species. Considering the remarkable regenerative capacity of this species, this genome will be an essential resource in future research efforts on molecular mechanisms regulating regeneration.

Articulated fossil ophiuroids from South America were reported for the Devonian, Cretaceous, Eocene, and Miocene. Here we report the first Jurassic record of an articulated ophiuroid from the Sierra Chacaicó Formation (early Pliensbachian-Sinemurian) in Neuquén Basin, Argentina, and discuss the taphonomic processes that allowed its preservation. The Sierra Chacaicó Formation represents the onset of the Early Jurassic extensive marine transgression in the basin. The basal section comprises shoreface and offshore Gilbert-type delta system, which was affected by hyperpycnal discharges. The middle and upper sections are represented by offshore deposits, affected by storms and eroded by hyperpycnal channel-levee systems. The ophiuroid specimen was found in levels of massive, fine, tuffaceous sandstone beds and covered by coarse sandstone containing a large amount of plant debris and organic matter. It was preserved articulated, with a complete disc and almost complete arms. Based on the microstructure of the spine-bearing lateral arm plates, the ophiuroid is assigned to Sinosura, an extinct genus of the family Ophioleucidae, widespread in the Lower Jurassic deposits of Europe but previously unknown from other parts of the world. The posture of the ophiuroid, with one arm curved distally and extended in one direction and the other four arms symmetrically oriented in the opposite direction, suggests a walking or escape movement frozen in time. This implies that the ophiuroid was buried alive by sediment thick enough to prevent successful escape. The taphonomic and sedimentologic evidence indicates that the fossil material was found in hyperpycnal deposits accumulated in offshore positions, which carried a high concentration of sediment in suspension. [ABSTRACT FROM AUTHOR]

Ophiuroidea is the most speciose of all classes of Echinoderma. It is an important component in benthic ecosystems, occurring in almost all ecological niches of modern seas. To date, the phylogeny and complete evolutionary history of the ophiuroids have not yet been fully resolved. In this study, we sequenced the complete mitochondrial genomes (mitogenomes) of Ophiothrix (Ophiothrix) exigua and two deep‐sea species Histampica sp. CS049 and Ophioplinthaca sp. M5261. These two deep‐sea ophiuroids displayed reversed strand‐compositional bias and rearranged gene orders. Thirteen distinct patterns of mitochondrial gene order among ophiuroid mitogenomes were detected, with two gene order newly found in Ophiuroidea. Our data supported the gene order found in all sampled Ophiuridae as the most likely ancestral order of all Ophiuroidea. To improve phylogenetic accuracy based on nucleotide differences, two different criteria were used for the analyses: (i) nucleotide sequence from all codon positions (PCG123); (ii) the NTE method ("Neutral Transitions Excluded") for ameliorating the misleading effects of a reverse strand bias in the data. The two methods confirmed the polyphyly of the orders Ophiacanthida and Amphilepidia. At family and genus level, Ophiuridae, Ophionotus and Ophioplinthus were not monophyletic. The most notable exception was that the NTE phylogeny showed low variation of branch length. NTE dataset generated younger age for most lower‐level nodes than that from PCG123 dataset. All analyses suggested that the ophiuroids radiation occurred around the Permian–Triassic mass extinction event, and the divergence time of the deep‐sea lineages was during the Cretaceous. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Regeneration is a post-embryonic developmental process common in Metazoa, which, despite obvious taxa-specific differences, can often share common principles and patterns. Among these, the distalization and (proximal) intercalation model successfully describes most animal regeneration phenomena. Stellate echinoderms (Crinoidea, Asteroidea, and Ophiuroidea) are particularly practical models for regeneration studies as the proximo-distal regrowth of their "segmental" arms, including the inner "continuous" yet homologous structures, i.e. radial water canal, radial nerve cord, and somatocoel, provide a unique opportunity to investigate the existence of evolutionarily shared regenerative patterns. In the present work, we comparatively examined the anatomy of arm regeneration in four stellate echinoderm species – the crinoid Antedon mediterranea, the asteroids Echinaster sepositus and Coscinasterias tenuispina, and the ophiuroid Amphipholis squamata. We observed that in all the models the distal elements, i.e. the apical blastema of crinoids, and terminal ossicle and tube foot of asteroids and ophiuroids, form in an early stage, followed by the proximal region, which develops in the proximal-to-distal direction. In all arms, the continuous structures develop before discrete lateral structures (e.g. ossicles and tube feet), and appear to provide materials that make the subsequent development possible. Overall, the model inferred from our study is compatible with those previously proposed for other animal models that involve processes of distalization and intercalation. The evidence of shared patterns suggests that at least some overall regeneration mechanisms have ancient origins and are well conserved throughout echinoderm and animal evolution. This study could help shed light on those evolutionarily conserved principles (patterns) among metazoan regeneration. [ABSTRACT FROM AUTHOR]

Background: Echinoderms are established models in experimental and developmental biology, however genomic resources are still lacking for many species. Here, we present the draft genome of Ophioderma brevispinum, an emerging model organism in the field of regenerative biology. This new genomic resource provides a reference for experimental studies of regenerative mechanisms. Results: We report a de novo nuclear genome assembly for the brittle star O. brevispinum and annotation facilitated by the transcriptome assembly. The final assembly is 2.68 Gb in length and contains 146,703 predicted protein-coding gene models. We also report a mitochondrial genome for this species, which is 15,831 bp in length, and contains 13 protein-coding, 22 tRNAs, and 2 rRNAs genes, respectively. In addition, 29 genes of the Notch signaling pathway are identified to illustrate the practical utility of the assembly for studies of regeneration. Conclusions: The sequenced and annotated genome of O. brevispinum presented here provides the first such resource for an ophiuroid model species. Considering the remarkable regenerative capacity of this species, this genome will be an essential resource in future research efforts on molecular mechanisms regulating regeneration. [ABSTRACT FROM AUTHOR]

A proposed new Ordovician asterozoan genus and species, Cantabrigiaster fezouataensis , has been recently described and assigned to the class Somasteroidea. An accompanying phylogenetic analysis treated twenty-two asterozoans and sixteen early non-asterozoans, one of the latter providing the outgroup. The phylogenetic hypothesis focused on derivation of the subphylum Asterozoa and emphasized the Crinoidea; Cantabrigiaster fezouataensis was interpreted as documenting a critical transition stage in the origin of the Asterozoa. The diagnosis for the proposed new generic name posits absence of ambital framework ossicles as the single character expression that distinguishes Cantabrigiaster among somasteroid genera. Ambital framework ossicular presence is documented here in the holotype and other members of type suite; Cantabrigiaster is synonymized with Villebrunaster Spencer and V. fezouataensis nov. comb. is redescribed. The data matrix for the former Cantabrigiaster phylogenetic analysis relies on an earlier study treating overall echinoderm construction. Expressions outlined in the earlier study are not amenable to transfer to a data matrix without evaluation of level of universality of each cited expression; such evaluations were not provided thereby leading to flawed phylogenetic conclusions that are rejected. An alternative hypothesis for the early history of the Asterozoa supported by aspects of the fossil record, that subphylum diversification preceded the origin of readily preserved skeletons, and therefore potentially no tenable pre-asterozoan outgroup candidate survives in the fossil record, has not been falsified. [ABSTRACT FROM AUTHOR]

Gastropods of the genus Mucronalia (Eulimidae) are known ectoparasites of brittle stars (Ophiuroidea). However, the identities of host species are only known for three of some ten described species in the genus. Here, we report associations of Mucronalia snails, including one new species, with ophiuroid hosts from Japan and New Caledonia: M. spp. aff. alba with Ophiomastix annulosa, Ophiomastix mixta, and Ophiocoma cynthiae; M. sp. cf. exquisita with Amphioplus (Amphioplus) sp.; Mucronalia ryukyuensis n. sp. with Ophionereis porrecta; and Mucronalia sp. with Amphiura velox. Mucronalia ryukyuensis n. sp. is described from Okinawa, southwestern Japan. The new species is characterized by its slender shell with a large body whorl and aperture compared with other species of the genus. Among Japanese congeners, the shell of the new species is most similar to that of M. exilis, but differs in having a teleoconch with less-convex whorls, regularly increasing in diameter. The present study corroborates Warén's (1983) general rule that eulimids in a single genus parasitize hosts of the same echinoderm class, and our records suggest that closely related species of Mucronalia tend to exploit hosts of a more restricted lineage. We also briefly discuss the divergence processes of Mucronalia snails, which likely involve host shifts and geographic isolation. [ABSTRACT FROM AUTHOR]

The fossil record of the Ophiuroidea is still patchy, especially in the Cenozoic. Only four species have been described from the entire Oligocene, which is in stark contrast to the present-day diversity counting more than 2000 species. Here, we describe two new species of ophiuroid, Ophiura tankardi sp. nov. and Ophiodoris niersteinensis sp. nov., from the Lower Oligocene of the Mainz Basin. The species are based on microfossils extracted from the sieving residues of bulk sediment samples from a flush drill in Nierstein, Rhineland-Palatinate. The new species belong to extant genera and add to the poor Oligocene fossil record of the class. Based on present-day distributions, the occurrence of Ophiodoris suggests deep sublittoral to shallow bathyal palaeodepths for the Nierstein area of the Mainz Basin. [ABSTRACT FROM AUTHOR]

We describe a new species of ophiodermatid brittle star from the Eastern Pacific: Ophioderma occultum sp. nov. This species has been mistakenly recorded since 1899 as a colour phase of one of its congeners, Ophioderma panamense. However, the integrative use of morphological and molecular data, and comparison with type material of other Eastern Pacific Ophioderma, led to its differentiation as a novel species. Ophioderma occultum sp. nov. is characterised by having radial shields and adoral shields covered with granules, dorsal arm plates divided typically into two pieces, and a particular colour pattern: a dark grey to brown body, and arms with subtle lighter transverse bands and parallel longitudinal white bands over some median and distal segments. Molecular information based on the mitochondrial genes cytochrome oxidase subunit I (COI) and 16S also supported the species' validity, coinciding with the morphological observations. In particular, the molecular marker 16S had not been used before for species delimitation in this genus and was proven here to be resolutive. In contrast to most species of Ophioderma from the area, Ophioderma occultum sp. nov. shows a restricted distribution to the northern Mexican Pacific (Gulf of California and islas Revillagigedo). This new species is the 10thOphioderma described from the Eastern Pacific and the 34th worldwide. [ABSTRACT FROM AUTHOR]

Brittle stars are one of the most diverse classes of echinoderms distributed worldwide in marine habitats. In this study, brittle stars were sampled by hand from the intertidal zone of the Persian Gulf's western part to the Oman Sea, from locations accessible without the need of a boat or diving equipment. Sampling time was set in the first days of the lunar month or at least the time of lowest tide in each day. The specimens were first immobilized in freshwater, then fixed in neutralized buffered formalin, and finally preserved in 70% ethanol after one week of fixation. Of 22 sampling points, seven localities yielded intertidal brittle stars (Macrophiothrix hirsuta cheneyi, Macrophiothrix elongata, and Ophiocoma scolopendrina) during the sampling period (December 2017-March 2018). Ophiocoma scolopendrina is reported for the first time from Dayyer and Nayband in the Persian Gulf. We also re-evaluated recently reported data on ophiuroids from the studied area. [ABSTRACT FROM AUTHOR]

Echinoderm pedicellariae are groups of specialized opposable spines (valves) that articulate on a baseplate. The valves of a pedicellaria act together to grasp items for prey capture, surface cleaning, or defense. Pedicellariae have long been known to occur in sea urchins and seastars, and many types for different functions have been described. Here we describe a type of pedicellaria in basketstars and snakestars in the euryalid family Gorgonocephalidae. Valves of gorgonocephalous pedicellariae have been described and illustrated as independent "hooklets" since the 1800s. Aside from one illustration in 1930, baseplates have been illustrated only since the 1980s, after the advent of the scanning electron microscope. The structure, arrangement, and operation of valves on baseplates warrant their recognition as a pedicellaria, analogous to those of sea urchins and seastars. The gorgonocephalous pedicellaria is a multi-valved, unstalked, crossed pedicellaria. It is described and illustrated here with recommended morphological terminology to facilitate future studies on biomechanics, histology, paleontology, and phylogenetics. [ABSTRACT FROM AUTHOR]

Most Palaeozoic brittle stars lack the fused arm ossicles (vertebrae) that facilitate the remarkable mode of walking that characterizes living forms. Here we describe a stem ophiuroid from the Herefordshire Lagerstätte (Silurian, Wenlock Series), which is exceptional in preserving the body cavity uncompacted and the long tube feet. We assign the specimen to the order Oegophiurida. The morphology of the arms and attitude of the specimen suggest that locomotion may have been achieved by arm propulsion combined with podial walking. This ophiuroid increases the diversity of echinoderm higher taxa with preserved soft parts represented in the Herefordshire Lagerstätte. [ABSTRACT FROM AUTHOR]

Ophiopholis mirabilis is a common species with a high population density on the western coasts of the northern Pacific Ocean. The number of O. mirabilis has been increasing recently in the scallop aquaculture zone (the Zhangzi Island area, northern Yellow Sea) in China. To explore the mechanism of its population variation, the reproductive cycle of O. mirabilis was investigated in this area (39°04'N; 122°51'E) from February 2017 through January 2018 and determined by the monthly gonad index (GI), histological examinations of the gonads and the oocyte size-frequency distribution. O. mirabilis had a clear annual reproductive cycle that was synchronous between males and females. Sea temperature and food availability played important roles in O. mirabilis reproduction. The GI value was less reliable for determining reproductive activity in O. mirabilis because the nutritive tissues within the gonads may be utilized to synthesize gametes, leading to a decrease in GI during maturation. The histological results also show that abundant nutritive phagocytes were present in the gonads of O. mirabilis, which, together with the germ cells, affected the weight of the gonads. In addition, the mature oocytes of O. mirabilis were relatively small (75–150 µm), indicating that the larval development was planktotrophic. This study provided insights into the reproductive patterns and biology of O. mirabilis and is an essential basis for the quantity control of this species in aquaculture areas. [ABSTRACT FROM AUTHOR]

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Rocky reefs of the northern Colombian Pacific (Chocó) are diverse ecosystems that are poorly studied. Echinoderms are one of the principal groups in these ecosystems with associations to different species, including benthic organisms in which they live and other species that use them as hosts. These relationships include fishes, sponges, seaweeds, cnidarians, polychaetes, bryozoans, crustaceans, mollusks, and other echinoderms. For this area, 22 associations were registered, including commensalism, epibionts and parasitism. This work constitutes the first report for the associations of Eucidaris thouarsii with Suberites aff. ficus, E. thouarsii with Ophiothela mirabilis, and Holothuria (Thymiosicia) impatiens with Encheliophis vermicularis. Associations of Pentaceraster cumingi with Zenopontonia soror, and Ophionereis annulata with Malmgreniella cf. variegata are new records for Colombia. This work also expands the range of hosts previously described for Ophiothela mirabilis and expands the distribution of the association between Diadema mexicanum and Echineulima cf. robusta. [ABSTRACT FROM AUTHOR]

Ophioderma cinerea (Müller & Troschel, 1842) is a species of warm water ophiuroid that lives primarily in rocky habitats in the tropical Atlantic. Competition for resources can be high in their habitat. Behavioral observations in aquaria led to a hypothesis that differences in body size may affect feeding strategies, and thus affect survivorship. It is widely accepted that echinoderm ontogenic growth is sigmoidal, with juveniles growing much faster than adults. Yet, it is not understood what affect this has on behavior. Individuals were kept in replicate experimental tanks. After a 3-d starvation period, each individual was exposed to a proteinaceous food stimulus. The animals were observed and a time measurement was taken to determine how long it took the animals to sense the food and to begin moving toward the food during both day and night. Smaller individuals were found to sense food significantly faster than larger ones, while no difference was observed for time-to-motion. Several explanations may support this finding. One of these explanations highlights how the need to compete with larger animals may have selectively adapted ontogenetically more sensitive chemoreceptors in smaller animals. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Multilocus multivariate analysis and multi-species coalescent were used for species delimitation. • Mitochondrial and nuclear evolutionary histories differed, challenging mitochondrial-based barcoding approaches. • Six Ophioderma species were delimited using 30 nuclear and mitochondrial markers. • Ophioderma speciation history is complex and included hybridization. • We propose that using multilocus genotypes can help resolving complex speciation histories. Abstract Accurate species delimitation is essential to properly assess biodiversity, but also for management and conservation purposes. Yet, it is not always trivial to accurately define species boundaries in closely related species due to incomplete lineage sorting. Additional difficulties may be caused by hybridization, now evidenced as a frequent phenomenon. The brittle star cryptic species complex Ophioderma longicauda encompasses six mitochondrial lineages, including broadcast spawners and internal brooders, yet the actual species boundaries are unknown. Here, we combined three methods to delimit species in the Ophioderma longicauda complex and to infer its divergence history: (i) unsupervised species discovery based on multilocus genotypes; (ii) divergence time estimation using the multi-species coalescent; (iii) divergence scenario testing (including gene flow) using Approximate Bayesian Computation (ABC) methods. 30 sequence markers (transcriptome-based, mitochondrial or non-coding) for 89 O. longicauda and outgroup individuals were used. First, multivariate analyses revealed six genetic clusters, which globally corresponded to the mitochondrial lineages, yet with many exceptions, suggesting ancient hybridization events and challenging traditional mitochondrial barcoding approaches. Second, multi-species coalescent-based analyses confirmed the occurrence of six species and provided divergence time estimates, but the sole use of this method failed to accurately delimit species, highlighting the power of multilocus genotype clustering to delimit recently diverged species. Finally, Approximate Bayesian Computation showed that the most likely scenario involves hybridization between brooders and broadcasters. Our study shows that despite strong incomplete lineage sorting and past hybridization, accurate species delimitation in Ophioderma was possible using a combination of complementary methods. We propose that these methods, especially multilocus genotype clustering, may be useful to resolve other complex speciation histories. [ABSTRACT FROM AUTHOR]

The article focuses on research which aims to determine how the ophiuroid nervous system performs complex decision making and locomotory actions under decentralized control. Information about the results, which show that brittle star arms must be connected by the nerve ring for coordinated locomotion however information can travel bidirectionally around the nerve ring so that it circumvents the severance, is presented.

Graphical abstract Highlights • 17 mtDNA genomes spanning Ophiuroidea used to explore phylogeny and gene order evolution. • mtDNA data support monophyletic Ophintegrida and Euryophiurida. • Only 3 mtDNA gene order arrangements observed and all sampled Euryalida with same order. • Euryalid gene order likely ancestral for Ophiuroidea. Abstract Brittle stars are conspicuous members of benthic ecosystems, fill many ecological niches and are the most speciose of all classes of echinoderms. With high levels of biodiversity, elucidating the evolutionary history of this group is important. Understanding of higher-level relationships within Ophiuroidea has been aided by multilocus nuclear data and DNA barcoding. However, the degree of consistency between mitochondrial and nuclear data within ophiuroids remains unclear and deserves further assessment. In this study, 17 mitochondrial genomes spanning the taxonomic breadth of Ophiuroidea were utilized to explore evolutionary relationships through maximum likelihood analyses, Bayesian inference and comparative assessment of gene order. Our phylogenetic analyses, based on both nucleotide and amino acid residues, support recent findings based on multilocus nuclear data and morphology, in that the brittle star clades Ophintegrida and Euryophiurida were recovered as monophyletic with the latter comprising Euyalida, Ophiuridae and Ophiopyrgidae. Only three different arrangements of the 13 protein coding and 2 ribosomal RNA genes were observed. As expected, tRNA genes were more likely to have undergone rearrangement but the order of all 37 genes was found to be conserved in all sampled Euryalida and Ophiuridae. Both Euryalida and the clade comprised of Ophiuridae and Ophiopyrgidae, each had their own conserved rearrangement of protein coding genes and ribosomal genes, after divergence from their last common ancestor. Euryalida has a rearrangement of the two ribosomal RNA genes, rrnS and rrnL , in contrast to Ophiuridae and Ophiopyrgidae, which had an inversion of the genes nad1 , nad2 , and cob relative to Ophintegrida. Further, our data support the gene order found in all sampled Euryalida as the most likely ancestral order for all Ophiuroidea. [ABSTRACT FROM AUTHOR]

Mitochondrial genomes provide an additional data source for nuclear phylogenomics. Recently, the taxonomic classification of Ophiuroidea was changed dramatically based on a molecular phylogenetic analysis that utilized a huge nuclear dataset of transcriptome and target-capture approaches. However, the mitochondrial genome analysis of Ophiuroidea was not conducted sufficiently in depth to allow comparison with current phylogenetic relationships, especially for the Ophintegrida. In this study, eight mitogenomes were newly reported in Amphilepidida and Ophiacanthida. Phylogenetic analyses were undertaken based on the nucleotide sequences of 13 protein coding genes (PCGs), 22 tRNA, and two rRNA, and the amino acid translated sequences of 13 PCGs. The results of the phylogenetic analysis suggested that the amino acid translated sequences were more useful than the nucleotide sequences for the analysis of higher phylogenetic relationships. The mitochondrial gene order of 13 PCGs and two rRNA in Amphilepidida and Ophiacanthida was relatively conserved. However, more complex gene orders occurred in the phylogeny of Amphilepidida and Ophiacanthida, including 22 tRNA. The results of our study suggest that Ophiuroidea has undergone more complex gene rearrangements than other classes of echinoderms. [ABSTRACT FROM AUTHOR]

Brittle stars (Phylum Echinodermata, Class Ophiuroidea) have evolved rapid locomotion employing muscle and skeletal elements within their (usually) five arms to apply forces in a manner analogous to that of vertebrates. Inferring the inner workings of the arm has been difficult as the skeleton is internal and many of the ossicles are sub‐millimeter in size. Advances in 3D visualization and technology have made the study of movement in ophiuroids possible. We developed six virtual 3D skeletal models to demonstrate the potential range of motion of the main arm ossicles, known as vertebrae, and six virtual 3D skeletal models of non‐vertebral ossicles. These models revealed the joint center and relative position of the arm ossicles during near‐maximal range of motion. The models also provide a platform for the comparative evaluation of functional capabilities between disparate ophiuroid arm morphologies. We made observations on specimens of Ophioderma brevispina and Ophiothrix angulata. As these two taxa exemplify two major morphological categories of ophiuroid vertebrae, they provide a basis for an initial assessment of the functional consequences of these disparate vertebral morphologies. These models suggest potential differences in the structure of the intervertebral articulations in these two species, implying disparities in arm flexion mechanics. We also evaluated the differences in the range of motion between segments in the proximal and distal halves of the arm length in a specimen of O. brevispina, and found that the morphology of vertebrae in the distal portion of the arm allows for higher mobility than in the proximal portion. Our models of non‐vertebral ossicles show that they rotate further in the direction of movement than the vertebrae themselves in order to accommodate arm flexion. These findings raise doubts over previous hypotheses regarding the functional consequences of ophiuroid arm disparity. Our study demonstrates the value of integrating experimental data and visualization of articulated structures when making functional interpretations instead of relying on observations of vertebral or segmental morphology alone. This methodological framework can be applied to other ophiuroid taxa to enable comparative functional analyses. It will also facilitate biomechanical analyses of other invertebrate groups to illuminate how appendage or locomotor function evolved. [ABSTRACT FROM AUTHOR]

A new genus of ophiuroid, Luxaster n. gen., is described based on articulated skeletal remains preserved as external molds. The new genus belongs to the Paleozoic stem-group family Protasteridae. It includes two species, Luxaster martini n. sp. from the Lower Devonian of Luxemburg, and Luxaster schweitzeri from the Lower Devonian of W-Germany. Within the Protasteridae, Luxaster stands out in showing a combination of characters best interpreted as strongly paedomorphic within the morphological spectrum of the family. This suggests that paedomorphosis played a role in ophiuroid evolution not only in the living clades but also in the extinct stem groups. [ABSTRACT FROM AUTHOR]

The discovery of a very large ophiuroid (disk diameter of 80 mm) in the early Permian (Kungurian) Cundlego Formation in the Southern Carnarvon Basin of Western Australia extends the stratigraphical range of ‘archaic’ ophiuroids unequivocally into the Permian, unlocking a lost fossil record of this group. Hitherto such ophiuroids have been discovered preserved articulated from strata no younger than the late Carboniferous. Herein we describe the new ophiuroid as Teleosaster creasyi gen. et sp. nov. Although existing temporally with Permian ophiuroids with a ‘modern’ morphological architecture, Teleosaster was biogeographically separated. This ‘archaic’ ophiuroid persisted in high latitude seas, suggesting such ‘archaic’ forms were displaced from the shallow-water, low latitude niches by the ‘modern’ ophiuroids. In modern oceans, ophiuroid gigantism similar to that in Teleosaster creasyi is typically only expressed in cold, high latitude oceans. It has been argued that the frequent occurrence of gigantism in such environments is due to the much lower levels of predation pressure. Unlike other echinoderm classes, the morphological and ecological transformation that resulted in the evolution of ‘modern’ ophiuroids had already taken place well before the events of the Permo-Triassic mass extinction. With the increase in diversity of durophagous predators in low latitude shallow-water communities during the mid-Palaeozoic Marine Revolution, we argue that ‘archaic’ ophiuroids were more susceptible to these higher levels of predation than the ‘modern’ forms and were displaced into regimes of lower predation pressure in high latitude oceans. http://zoobank.org/urn:lsid:zoobank.org:pub:E4FD9264-127D-4995-AD12-C9721F212FCD [ABSTRACT FROM AUTHOR]

The fossil record of Paleozoic ophiuroids includes a number of forms which share striking similarities with modern relatives in terms of skeletal morphology. These so called modern-type Paleozoic ophiuroids yield an enormous potential for a better understanding of ophiuroid evolution, yet the scarcity of accurate and sufficiently detailed morphological descriptions available to date precludes any further-reaching assessments. Here, we describe an articulated ophiuroid specimen from the Late Tournaisian (early Carboniferous) of Czatkowice quarry, southern Poland, as a new species Aganaster jagiellonicus sp. nov. The good preservation of the specimen allowed for a morphological analysis at a level comparable to recent ophiuroid descriptions. It shows remarkable morphological similarities with extant former ophiolepidids Ophiomusium and Ophiosphalma. The new find thus contributes to a solid basis for future investigations on the position of the modern-type Paleozoic ophiuroid in the phylogeny of the class.

The peristomial plates are skeletal components of the interbrachial frame (or mouth frame), which is located below the true mouth of ophiuroids. Whilst the peristomial plates were extensively described and used as diagnostic characters by some early workers, for the past 100 years they have been largely neglected as a taxonomic resource. In this investigation the peristomial plates of 48 species representing 21 families were examined directly, and information on a further 61 species, including representatives of another eight families, was obtained from the published literature. Observations were made with regard to fragmentation state, relative size and orientation of the peristomial plates. Although fragmentation state showed little consistency at any taxonomic level, relative size and orientation segregated a group of families comprising species with relatively small, inclined peristomial plates, viz. Ophiotrichidae, Ophiopholidae, Ophiactidae, Amphiuridae and Ophiocomidae, together with a single hemieuryalid species–Ophioplocus januarii. The distribution of peristomial plate traits was strongly correlated with that of several other character states pertaining to the interbrachial frame. This supported the proposition that two major types of interbrachial frame are present in ophiuroids (designated ‘A’ and ‘B’). Current phylogenies inferred from both morphological and molecular data imply that type B is derived and has evolved independently at least twice in the orders Amphilepidida and Ophiacanthida. This represents a remarkable example of evolutionary convergence. An analysis of the distribution of all interbrachial frame character states suggested that within the Amphilepidida paedomorphosis was probably responsible for the complete reversion of the interbrachial frame to the ancestral type A condition in two families (Ophiothamnidae and Amphilepididae) of suborder Gnathophiurina and possibly responsible for varying degrees of trait reversal in the four families of suborder Ophionereidina. Such paedomorphic events may have been associated with a secondary return to the deep-sea from shallow-sea environments. [ABSTRACT FROM AUTHOR]

The first phylogenetic and phylogeographic studies of the cosmopolitan deep-sea species, Asteronyx loveni Müller and Troschel, 1842, were conducted, based on specimens collected from off the Pacific coast of Japan. Partial sequences of mitochondrial 16S (68 specimens) and COI (24 specimens) genes were analyzed. Phylogenetic trees and network analyses revealed three lineages and five sub-lineages of A. loveni . Genetic distance and AMOVA (analysis of molecular variance) analyses suggested that the lineages should be considered three cryptic species. Skin on the aboral disc is partly thickened and forms a mesh-like pattern, which has never been reported in previous descriptions of Asteronyx ; this is provided as a new taxonomic character. Based on absence/presence of mesh-like skin, one of the three lineages was assigned to A. loveni and another was described as Asteronyx reticulata new species. This new species can be distinguished from congeners by having mesh-like skin and small genital slits at the innermost position on the interradial oral disc. [ABSTRACT FROM AUTHOR]

The Mg/Ca and Sr/Ca ratios in echinoderm skeletal calcite are used as a proxy for Phanerozoic seawater changes, since the skeletal concentrations are, to some extent, controlled by environmental factors. However, it remains unclear how the influence of environmental factors is modified by vital effects, especially in polar waters. Therefore, the goal of this study was to compare the ratios of Mg/Ca and Sr/Ca among the skeletal parts of 10 common Arctic echinoderm species belonging to three classes Echinoidea, Asteroidea and Ophiuroidea that contribute substantially to the carbon cycle in the Arctic benthic system. Significant differences were recorded in echinoid skeletal element concentrations among specific skeletal parts. The lowest Mg/Ca and Sr/Ca ratios were detected in the spines (mean Mg/Ca 37.5 ± 8.8 SD; Sr/Ca 1.8 ± 0.1). The components of the Aristotle's lantern (epiphyses, pyramids and rotulas) were characterised by the highest Mg levels (Mg/Ca 79.9 ± 6.0; 75.2 ± 9.1; 60.1 ± 3.8, respectively). It is likely that mouth parts experience greater mechanical pressure compared to other body parts, and the higher content of Mg in the Aristotle's lantern contributes to its robustness. We did not find any distinctive trends in the distribution of skeletal elements in the asteroid and ophiuroid skeletal parts. The heterogeneous concentrations of Mg and Sr in different skeleton parts of the echinoids suggest possible physiological regulation of the chemical composition rather than the composition only being influenced by the environment. We cannot recommend echinoderm skeletons as reliable indicators in palaeoenvironmental reconstructions due to the possible biological control of skeletal chemistry, which may interfere with the effect of environmental variables. [ABSTRACT FROM AUTHOR]

The brittle star Ophiothela cf. mirabilis, an ophiuroid introduced in the Atlantic, has expanded its range north to Trinidad and Tobago and south to Paraná, Brazil. By monitoring the coast of Santa Catarina, Brazil, with both recruitment plates in harbors and scuba diving, we were able to observe specimens of O. cf. mirabilis in both natural and anthropogenic habitats. This confirms its reported range extension of roughly 80 km south and emphasizes the importance of anthropogenic means for their spread and establishment. [ABSTRACT FROM AUTHOR]

Background: Brittle stars (Ophiuroidea, Echinodermata) have been increasingly used in studies of animal behavior, locomotion, regeneration, physiology, and bioluminescence. The success of these studies directly depends on good working knowledge of the ophiuroid nervous system. Results: Here, we describe the arm nervous system at different levels of organization, including the microanatomy of the radial nerve cord and peripheral nerves, ultrastructure of the neural tissue, and localization of different cell types using specific antibody markers. We standardize the nomenclature of nerves and ganglia, and provide an anatomically accurate digital 3D model of the arm nervous system as a reference for future studies. Our results helped identify several general features characteristic to the adult echinoderm nervous system, including the extensive anatomical interconnections between the ectoneural and hyponeural components, neuroepithelial organization of the central nervous system, and the supporting scaffold of the neuroepithelium formed by radial glial cells. In addition, we provide further support to the notion that the echinoderm radial glia is a complex and diverse cell population. We also tested the suitability of a range of specific cell-type markers for studies of the brittle star nervous system and established that the radial glial cells are reliably labeled with the ERG1 antibodies, whereas the best neuronal markers are acetylated tubulin, ELAV, and synaptotagmin B. The transcription factor Brn1/2/4 - a marker of neuronal progenitors - is expressed not only in neurons, but also in a subpopulation of radial glia. For the first time, we describe putative ophiuroid proprioceptors associated with the hyponeural part of the central nervous system. Conclusions: Together, our data help establish both the general principles of neural architecture common to the phylum Echinodermata and the specific ophiuroid features. [ABSTRACT FROM AUTHOR]

Ophioconis claviculata sp. nov. is described on the basis of three specimens collected from Ryukyu Islands, southwestern, Japan. The new species is distinct in having: disc covered by granules; four, sometimes five flat, polygonal oral papillae on each side of jaw; broad and flat teeth with hyaline distal end; spiniform and conical arm spines, two times longer than the corresponding arm segment at the maximum length; oralmost arm spines on proximal portion of arms flattened and clavate; four tentacle scales on third tentacle pore; and ventral arm plate longer than wide, with concentrate lamellar striations. The new species was found under rocks of open water as well as in a dark and medium to low salinity (28 ppt) environment of submarine cave, suggesting that this species tolerate this specific condition. [ABSTRACT FROM AUTHOR]

The distributional records of Ophiuroidea stored at the Italian National Antarctic Museum (MNA, Section of Genoa) are presented, corresponding to 1595 individuals that belong to 35 species and 17 genera. Specimens were collected in 106 different sampling stations at depths ranging from 21 to 1652 m in the framework of 14 Antarctic expeditions to the Ross Sea, one to the Antarctic Peninsula, and one to the Falkland Islands (Islas Malvinas). Three species, Amphiura joubini Koehler, 1912, Amphiura (Amphiura) angularis Lyman, 1879, and Ophiura flexibilis (Koehler, 1911), are reported as new records for the Terra Nova Bay area, whose check-list of species increases from 15 to 18 species. The determination of these three new records was based both on morphological identification and molecular analyses (COI barcoding). Some of the genetically characterised specimens were also documented through photogrammetry and micro-computed tomography and represent the first bulk of 3D models that will be available through the MNA and Sketchfab websites, both for research and educational purposes. [ABSTRACT FROM AUTHOR]

Echinoderms are widely used to investigate the relationship between egg size, energy content and larval developmental strategies in marine invertebrates; although there have been few studies on ophiuroids and holothuroids. In this paper, we provide the first detailed biochemical information on egg composition and utilization in the planktotrophic holothuroid, Australostichopus mollis. The egg ultrastructure, protein content (85.1 ng egg) and lipid:protein ratio of 0.42 were consistent with those of other planktotrophic echinoderms of similar egg size. However, the lipid content (35.6 ng egg) was outside the 95% prediction band for the relationship between egg size and lipid content for echinoderms. Triacylglycerol (TAG) was the main energetic lipid present in the egg, with ca 50% of the TAG being utilized to construct the feeding auricularia; the remaining TAG was estimated to be consumed over 114.8 h (4.8 days) of development. Feeding a microalgal diet during early larval development did not affect the rate of TAG utilization, but increased protein content in the 90-h auricularia. Biochemical information from A. mollis eggs/larvae suggests that TAG might be the ancestral maternally derived energetic lipid in the Echinodermata, but also that there may be different patterns of lipid utilization between different classes. [ABSTRACT FROM AUTHOR]

The reproduction of the brittle star Astrotoma agassizii was studied from deep waters of the South Atlantic Ocean, based on samples collected in August 2012, and May and September 2013. Ten samples from 800 to 1400 m depths off Mar del Plata Canyon were studied. The species was found to be a brooding simultaneous hermaphrodite. Hermaphroditic gonads contained testis and ovaries inside the same sacs. Both, ovary and testis contained different stages of gametogenesis development simultaneously. Gonads contained several stages of oocytes in different stages of gametogenesis. The largest oocyte recorded was 800 µm diameter. Free spermatozoa were observed in the lumen of the testis, together with spermatogenic columns. Five individuals, from a total of 30 examined, resulted brooding, and most contained mature ovotestis at the same time. Incubation occurs in five of the ten bursal sacs, containing 15–20 young juveniles each. Maximum disc diameter recorded for a brood was 1100 µm. Herein we hypothesize that Astrotoma agassizii could be continuous breeder species in the deep-sea. [ABSTRACT FROM AUTHOR]

The power and throughput of next-generation sequencing is instigating a major transformation in our understanding of evolution and classification of life on our planet. The new trees of life are robust and comprehensive. Here we provide a landmark phylogeny of the living ophiuroids and use it as the basis for a major revision of the higher classification of this class of marine invertebrates. We used an exon-capture system to generate a 1484 exon (273 kbp) data-matrix from DNA extracted from ethanol-preserved museum samples. We successfully obtained an average of 90% of our target sequence from 576 species spread across the known taxonomic diversity. The topology of the major lineages was robust to taxon sampling, exon-sampling, models and methods. However, estimates of node age were much less precise, varying by about a quarter of mean age. We used a combination of phylogenetic distinctiveness and temporal-banding to guide our revision of the family-level classification. Empirically, we determined that limiting family crown age to 110 ± 10 Ma (mid Cretaceous) selected phylogenetically distinct nodes while minimising disruption to the existing taxonomy. The resulting scheme of 32 families and six orders considerably expands the number of higher taxa. The families are generally longitudinally widespread across the world’s oceans, although 17 are largely confined to temperate and equatorial latitudes and six to relatively shallow water (less than 1000 m depth). [ABSTRACT FROM AUTHOR]

A Lochkovian (Early Devonian) ophiuroid (Echinodermata), Ophiocantabria elegans n. gen. and sp., is based on a single small, well-preserved specimen collected from a shale-rich horizon of the Furada Formation, Asturias, Spain. Sedimentologic and palaeontologic data suggest its occurrence was in a near-shore setting subjected to frequent storms. Ophiocantabria is assigned to the Encrinasteridae based on the morphology of individual skeletal elements, although overall form of the new species is similar to that of approximately coeval members of the asteroid family Xenasteridae. Such homoplasy, especially among earlier members of asterozoan class-level clades, is an important but not well understood aspect of subphylum evolution.

The gogiid eocrinoid Akadocrinus jani Prokop, 1962 is known from the mid-Cambrian (Drumian) Jince Formation of the Příbram-Jince Basin (Barrandian area, Czech Republic). Excellently preserved specimens of this species are described in detail. Our primary focus was on juvenile specimens, described here for the first time. Detailed comparison among juvenile specimens makes it possible to establish changes in morphology during ontogeny. Juvenile specimens differ considerably from adult specimens in (1) a lower number of thecal plates, (2) a complete absence of epispires, (3) comparatively shorter brachioles, comprising a small number of brachiolar plates, (4) a comparatively shorter stem, comprising a small number of columnals and (5) a relatively large attachment disc. Study of the Jince material makes it possible to establish two basic phases in the development of Akadocrinus: the pre-epispire bearing phase and the epispire bearing phase. [ABSTRACT FROM AUTHOR]

Brooding in ophiuroids (Echinodermata: Ophiuroidea) is a highly-developed reproduction strategy and has evolved independently several times. In South African waters, brooding occurs both in the very small amphiuridAmphipholis squamata, which is hermaphroditic, and in the large ophiodermatidOphioderma wahlbergii, which is gonochoric. For the first time, microcomputed tomography was applied to visualise and compare brooding and brooded young of these two brittle star species from two distantly related families. The scannedA. squamatabrooded six young, whereasO. wahlbergiibrooded 13 young. Volume measurements of the adults revealed thatA. squamatadedicated about 25% of its disc volume to brooding andO. wahlbergiiabout 14%. Although the brooded young ofO. wahlbergiiare thought to be among the largest of all known ophiuroids, young ofA. squamatawere four times larger in relation to adult body disc volume. Other than differences in the sizes of brooded young, these distantly related species have evolved very similar brooding adaptations. All juveniles were found lying with the mouth upward, pressed against the mother's bursal wall, strengthening the hypothesis that the bursal wall acts as a nutritive organ. In both species, the large size of the young can only be explained by maternal nutrient supply. Both brittle star species, therefore, are regarded as truly viviparous. [ABSTRACT FROM AUTHOR]

The fossil record of Paleozoic ophiuroids includes a number of forms which share striking similarities with modern relatives in terms of skeletal morphology. These so called modern-type Paleozoic ophiuroids yield an enormous potential for a better understanding of ophiuroid evolution, yet the scarcity of accurate and sufficiently detailed morphological descriptions available to date precludes any further-reaching assessments. Here, we describe an articulated ophiuroid specimen from the Late Tournaisian (early Carboniferous) of Czatkowice quarry, southern Poland, as a new species Aganaster jagiellonicus sp. nov. The good preservation of the specimen allowed for a morphological analysis at a level comparable to recent ophiuroid descriptions. It shows remarkable morphological similarities with extant former ophiolepidids Ophiomusium and Ophiosphalma. The new find thus contributes to a solid basis for future investigations on the position of the modern-type Paleozoic ophiuroid in the phylogeny of the class. [ABSTRACT FROM AUTHOR]

The fiords of southwestern New Zealand may promote the existence of genetically divergent populations as a result of geological and ecological isolation. The ophiuroidAstrobrachion constrictumlives on black coral in these fiords, and is thought to have a relatively short pelagic larval duration that may limit dispersal among populations. Samples ofA. constrictumwere collected from seven sites (four fiords) in Fiordland. Analysis of the mitochondrial COI gene using single-stranded conformational polymorphism revealed eight haplotypes, representatives of which were sequenced. These included nine variable sites, none of which were phylogenetically informative.G-test and AMOVA revealed little structuring of samples within or among fiords, but there was evidence for reduced gene flow among the most geographically separated fiords. We conclude that fiords do not house relict populations from earlier glaciations, and that little differential sorting of haplotypes has occurred in the last 10,000 years. [ABSTRACT FROM PUBLISHER]

Ophiuroids were collected during the Singapore Biodiversity Workshop at Pulau Ubin in 2012. About 520 specimens were provisionally identified and 22 species of ophiuroids recognised. Fourteen species are new to Singapore waters. [ABSTRACT FROM AUTHOR]

Sea cucumbers (Holothuroidea) are known to host ectocommensal animals but echinoderm epibionts have never been reported nor their effects on hosts appraised quantitatively. At one location in New Caledonia, we found a high number of ophiuroids (Ophiothelacf.danae) and synaptid sea cucumbers (Synaptula mediaandSynaptulasp.) living on the bumpy external body wall of sea cucumbers,Stichopus herrmanni. Rates of midday sediment defecation (mean: 23 g h−1) and short-term displacements (mean: 60 cm h−1) by the hosts were not significantly affected by the number of echinoderm commensals they carried. The frequent relationships at the location suggest that such facultative commensalism between echinoderms could be more common than previously understood. Appreciable numbers of scaleworms, crabs and shrimps on the sea cucumbers show that sea cucumbers can act as hosts to echinoderms and other epibiotic taxa, bolstering the notion that they play important ecological roles in reef ecosystems. [ABSTRACT FROM PUBLISHER]