Ophiuroids Research Articles

Spatiotemporal variations in the population dynamics of a few prominent brittle star species (Echinodermata: Ophiuroidea) from the intertidal flat of the Veraval coast, Gujarat, India

The present communication reports the spatiotemporal variation in the population dynamics of three prominent Ophiuroidea species: Amphipholis squamata, Ophiactis savignyi and Ophiocomella sexradia at the rocky intertidal zone at Veraval (21°35’ N, 69°36’ E) Gujarat, off the Arabian Sea. The two sampling areas with different substratum and community structures were investigated from April 2019 to March 2020. Brittle stars were found inhabited in the coralline bed, zoanthid bed, algal holdfast, rock pool crevices and underneath rocks in the studied coastal areas. A. squamata was the most abundant species followed by O. savignyi and O. sexradia at the Veraval coast. The current study described a few remarkable revelations between the patches of coralline algae and Ophiuroidea abundance. Brittle star population revealed major spatial variations between both sampling sites. Cluster analysis and nMDS support population abundance in a seasonal pattern distribution.

Megabenthic biodiversity in culturally and ecologically important coastal regions of Northern Labrador

Labrador Inuit have expressed concern about the impacts of climate change on their health and well-being and their future access to marine resources, including fisheries. This study filled important knowledge gaps identified by the Nunatsiavut Government and Inuit communities regarding benthic biodiversity and habitat structure within major geomorphology features. Marine benthic surveys were conducted in three areas of ecological, cultural, and historical significance: Hebron Fjord, Okak Fjard, and the Nain archipelago, inclusive of a polynya, using a camera sled and a baited remote underwater video system. We documented the spatial extent of megabenthic diversity components and the high densities of dominant taxa, notably tube-dwelling anemones (cerianthids), brittle stars (ophiuroids), soft corals (<em>Gersemia</em> sp.), and bristle worms (polychaetes). Species accumulation curves indicated that new species records are likely to be discovered. Vulnerable marine ecosystem (VME) indicator species and other key taxa provide seafloor structure for mobile species and important ecosystem functions, such as energy cycling, especially in the deeper areas of the fjord and fjard that are dominated by soft sediment. The sites with the highest benthic diversity, including the greatest densities of scallops and fish fauna, were in the archipelago and polynya, areas frequently used by Inuit for traditional harvesting. These findings were suggestive of a more direct linkage between these areas and trophic levels of greatest importance to Labrador Inuit. Understanding these patterns from the combined perspectives of Inuit and Western science in Nunatsiavut marine waters will guide resource management and protected area decisions, including those in the Nunatsiavut Government’s Imappivut Marine Planning Initiative.

The evolutionary relationship between arm vertebrae shape and ecological lifestyle in brittle stars (Echinodermata: Ophiuroidea).

Ophiuroidea are one of the most diverse classes among extant echinoderms, characterized by their flexible arms composed of a series of ossicles called vertebrae, articulating with each other proximally and distally. Their arms show a wide range of motion, important for feeding and locomotion, associated with their epizoic and non-epizoic lifestyles. It remains to be explored to what degree the phenotypic variation in these ossicles also reflects adaptations to these lifestyles, rather than only their phylogenetic affinity. In this study, we analyzed the 3D shape variation of six arm vertebrae from the middle and distal parts of an arm in 12species, belonging to the intertidal, subtidal and bathyal zones and showing epizoic and non-epizoic behaviors. A PERMANOVA indicated a significant difference in ossicle morphology between species and between lifestyles. A principal component analysis showed that the morphology of epizoic ophiuroids is distinct from non-epizoic ones; which may reflect variation in arm function related to these different lifestyles. The Phylogenetic MANOVA and phylogenetic signal analysis showed that shape variation in the vertebral articulation seems to reflect ecological and functional adaptations, whereas phylogeny controls more the lateral morphology of the vertebrae. This suggests a convergent evolution through ecological adaptation to some degree, indicating that some of these characters may have limited taxonomic value.

Overlooked biodiversity of brittle stars from the Upper Pleistocene of Japan: descriptions of fossil ossicle assemblage in Indo-West Pacific

ABSTRACT Disarticulated fossil ossicles of brittle stars from the Upper Pleistocene Yokosuka Formation, Yokosuka, Kanagawa Prefecture, central Japan, are described. The ossicles of lateral arm plates and vertebrae are assigned to Gorgonocephalidae, Ophiocomidae, Ophiosphalmidae, Ophiopholis, Ophiothrix, Ophiarachnella, Stegophiura sladeni, Ophiuroglypha kinbergi and Ophiozonella longispina, on the basis of external morphology. This is the first faunal record mainly based on disarticulated fossil lateral arm plates of brittle stars from the Indo-Pacific region.

Alien hotspot: Benthic marine species introduced in the Brazilian semiarid coast

In this study, we provide a baseline assessment of introduced marine species along the extensive (~600 km) Brazilian semiarid coast. We reported 27 introduced and 26 cryptogenic species. Moreover, the main vectors of introduction were ballast water, shipping lines, oil and gas activities, biofouling, and rafting on plastic debris. The taxa were Ascidiacea (17 species) and Bryozoa (17), followed by Crustacea (6), Mollusca (6), Cnidaria (3), Echinodermata (3), and Porifera (1). Among these invertebrates, some species are recognized as drivers of impacts such as the invasive corals (Tubastraea tagusensis and Tubastraea coccinea), the bivalves Isognomom bicolor and Perna viridis, the crab Charybdis hellerii, the brittle star Ophiothela mirabilis, and, finally, the bryozoan Membraniporopsis tubigera. These species threaten the biodiversity of unique ecosystems such as intertidal sandstone reefs, shallow-water coral reefs, and mesophotic ecosystems. Moreover, the up-to-date results highlight that this region is a hotspot of bioinvasion in the tropical South Atlantic.

Neuroecology beyond the brain: learning in Echinodermata.

We propose an expansion of neuroecological comparisons to include the capabilities of brainless and non-neural organisms. We begin this enterprise by conducting a systematic search for studies on learning in echinoderms. Echinodermata are marine invertebrates comprising starfish, brittle stars, sea cucumbers, sea urchins, and sea lilies. Animals in this phylum lack any centralized brain and instead possess diffuse neural networks known as nerve nets. The learning abilities of these animals are of particular interest as, within the bilaterian clade, they are close evolutionary neighbors to chordates, a phylum whose members exhibit complex feats in learning and contain highly specialized brains. The learning capacities and limitations of echinoderms can inform the evolution of nervous systems and learning in Bilateria. We find evidence of both non-associative and associative learning (in the form of classical conditioning) in echinoderms, which was primarily focused on starfish. Additional evidence of learning is documented in brittle stars, sand dollars, and sea urchins. We then discuss the evolutionary significance of learning capabilities without a brain, the presence of embodied cognition across multiple groups, and compare the learning present in echinoderms with the impressive cognitive abilities documented in the oldest linage group within vertebrates (the major group within the phylum of chordates), fish.

Range extension and first record of the deep-sea brittle star Ophiactis abyssicola (Echinodermata: Ophiuroidea) in Canadian waters

AbstractThis paper presents the first records of the brittle star Ophiactis abyssicola in Canadian waters and range extensions of up to 1900 km in the Northwest Atlantic from previously known locations. Samples were collected off northern Labrador and the northern portion of insular Newfoundland (eastern Canada) at 433 and 1097 m depths, respectively. This newly recorded species of brittle star from the bathyal zone off Newfoundland and Labrador adds to the marine biodiversity of Canada and to the general distribution knowledge of O. abyssicola.

A new deepwater lobster, Metanephrops serendipitus sp. nov. (Crustacea, Decapoda, Nephropidae), from lower Miocene of Meljski hrib (Maribor, Slovenia)

A new species of nephropid lobster, Metanephrops serendipitus sp. nov., is described from the lower Miocene (Ottnangian/Karpatian) in beds of Central Paratethys. Metanephrops serendipitus sp. nov. represents the first fossil representative of the genus from the northern hemisphere and thus extends its known palaeobiogeographical distribution. Additionally, the palaeoecology of the new species is discussed. Similar to extant species of Metanephrops, the fossil nephropid inhabited a fine-grained deep-sea environment, associated with frequent brittle stars.

Evolutionary innovations in Antarctic brittle stars linked to glacial refugia.

The drivers behind evolutionary innovations such as contrasting life histories and morphological change are central questions of evolutionary biology. However, the environmental and ecological contexts linked to evolutionary innovations are generally unclear. During the Pleistocene glacial cycles, grounded ice sheets expanded across the Southern Ocean continental shelf. Limited ice‐free areas remained, and fauna were isolated from other refugial populations. Survival in Southern Ocean refugia could present opportunities for ecological adaptation and evolutionary innovation. Here, we reconstructed the phylogeographic patterns of circum‐Antarctic brittle stars Ophionotus victoriae and O. hexactis with contrasting life histories (broadcasting vs brooding) and morphology (5 vs 6 arms). We examined the evolutionary relationship between the two species using cytochrome c oxidase subunit I (COI) data. COI data suggested that O. victoriae is a single species (rather than a species complex) and is closely related to O. hexactis (a separate species). Since their recent divergence in the mid‐Pleistocene, O. victoriae and O. hexactis likely persisted differently throughout glacial maxima, in deep‐sea and Antarctic island refugia, respectively. Genetic connectivity, within and between the Antarctic continental shelf and islands, was also observed and could be linked to the Antarctic Circumpolar Current and local oceanographic regimes. Signatures of a probable seascape corridor linking connectivity between the Scotia Sea and Prydz Bay are also highlighted. We suggest that survival in Antarctic island refugia was associated with increase in arm number and a switch from broadcast spawning to brooding in O. hexactis, and propose that it could be linked to environmental changes (such as salinity) associated with intensified interglacial‐glacial cycles.

A new phosphatized ophiuroid from the lower Triassic of Nevada and its position in the evolutionary history of the Ophiuroidea (Echinodermata).

The Lower Triassic fossil record of brittle stars is relatively rich, yet most records published to date are based on poorly preserved or insufficiently known fossils. This hampers exhaustive morphological analyses, comparison with recent relatives or inclusion of Early Triassic ophiuroid taxa in phylogenetic estimates. Here, we describe a new ophiuroid from the Lower Triassic of Nevada, preserved as phosphatized skeletal parts and assigned to the new taxon Ophiosuperstes praeparvus gen. et sp. nov Maxwell, V. Pruss. S.B. This unusual preservation of the fossils allowed for acid-extraction of an entire suite of dissociated skeletal parts, including lateral arm plates, ventral arm plates, vertebrae and various disk plates, thus unlocking sufficient morphological information to explore the phylogenetic position of the new taxon. Bayesian phylogenetic inference suggests a basalmost position of O. praeparvus within the Ophintegrida, sister to all other sampled members of that superorder. The existence of coeval but more derived ophiuroids suggests that O. praeparvus probably represents a member of a more ancient stem ophintegrid group persisting into the Early Triassic.

Automated Quantification of Brittle Stars in Seabed Imagery Using Computer Vision Techniques.

Underwater video surveys play a significant role in marine benthic research. Usually, surveys are filmed in transects, which are stitched into 2D mosaic maps for further analysis. Due to the massive amount of video data and time-consuming analysis, the need for automatic image segmentation and quantitative evaluation arises. This paper investigates such techniques on annotated mosaic maps containing hundreds of instances of brittle stars. By harnessing a deep convolutional neural network with pre-trained weights and post-processing results with a common blob detection technique, we investigate the effectiveness and potential of such segment-and-count approach by assessing the segmentation and counting success. Discs could be recommended instead of full shape masks for brittle stars due to faster annotation among marker variants tested. Underwater image enhancement techniques could not improve segmentation results noticeably, but some might be useful for augmentation purposes.

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.

Hadal fauna of the South Sandwich Trench, Southern Ocean: Baited camera survey from the Five Deeps Expedition.

The South Sandwich Trench is a 965 km long arcuate subduction trench spanning the South Atlantic and Southern oceans, isolated from most other hadal (areas where water depths exceed 6000 m) environments by thousands of kilometres. This feature represents the coldest known hadal ecosystem with ambient sub-zero temperatures recorded from bathyal depths to over 7000 m water depth. Very little research has been carried out into the hadal fauna of this trench since the Russian expeditions of the 1960s and 70s. Here, we report the first visual assessment of hadal fauna from the South Sandwich Trench from a series of seven baited camera and trap deployments between 6044 m and the deepest point at 8265 m water depth, a location called Meteor Deep. Three species of hadal fish (Liparidae), with very low population densities were observed at depths shallower than expected, likely due to the piezo-thermal effect decreasing their depth range. Four species of scavenging amphipods were recovered, extending the known distribution of Eurythenes andhakarae, Hirondellea dubia, and Bathycallisoma schellenbergi to the South Sandwich Trench. Large densities of brittle stars (Ophiuroidea) were seen in the shallower hadal depths, while dense aggregations of holothurians (Elpididae) were observed within trench-fill basins located along the deep trench axis coincident with a visible surficial layer of surface derived detritus. In addition, gastropods, sponges, and stalked crinoids were observed. Importantly, this study highlights the endemic community present at hadal depth within this somewhat unique high pressure-low temperature environment.

Callogorgia spp. and Their Brittle Stars: Recording Unknown Relationships in the Pacific Ocean and the Caribbean Sea

The habitat formed by the Callogorgia species, with their abundance and colony sizes, provides an important refuge for a variety of brittle stars which are recognized as the epibionts of octocorals in both shallow and deep environments. In such a relationship, ophiurans benefit directly from being elevated because they facilitate their feeding by suspension, while octocorals do not seem to benefit or be harmed. During three different expeditions developed in the Colombian Pacific from 2012 to 2013 and in the Caribbean Sea during 1998 and 2012 by the INVEMAR - Marine and Coastal Research institute, different samplings were carried out on soft bottoms through trawls with an epibenthic net. For the Pacific Ocean, 33 fragments of the octocoral Callogorgia cf. galapagensis Cairns, 2018 with 178 specimens of the ophiuroid Astrodia cf. excavata (Lütken and Mortensen, 1899) were found in two stations at depths 530 and 668 m. Considering the abundance of A. cf excavata, other biological characters such as size, presence of mature gonads, and evidence of arm regeneration were also detailed. In contrast, in the Caribbean Sea, Callogorgia gracilis (Milne Edwards and Haime, 1857) was found with ophiuroids belonging to the genera Asteroschema and Ophiomitra. The octocoral Callogorgia americana (Cairns and Bayer, 2002) was also found, but without associated brittle stars. These findings constituted the first specific association reported in the Eastern Tropical Pacific, and new relationships for the Caribbean Sea. This further reflected a possible specific association between the Callogorgia and Astrodia species that needed to be further explored. Thus, the Callogorgia species and the brittle star A. cf. excavata represented new records for the Colombian Pacific Ocean and the southern Caribbean Sea.

Impacts of infaunal activity and physical disturbance on acoustic properties of muddy coastal sediments

Storm disturbance of shallow coastal sediments can resuspend subtidal sediment and transport and deposit sand from beach erosion, creating sorted layers of differing grain sizes. These sediments provide habitat for diverse and abundant infaunal organisms that mix these layers (bioturbation), but how the reestablishment of disturbance-tolerant infauna affects recently disturbed sediment structure, including acoustic properties, is poorly understood. In this laboratory study, we compared the effects of physical disturbance (resuspension of surface muddy sediment and addition of sand, simulating a storm), infaunal activities (burrowing by brittle stars), and the combination of both on acoustic properties of sediments. We hypothesized that acoustic properties would reflect faster reconsolidation and more mixing of the initial mud layer with the deposited sand in sediment with infauna compared to defaunated sediment. At several timepoints following disturbance (1–14 days), we measured sound speed and attenuation at 400 kHz at multiple depths within and below the resuspended layer. After 14 days, we measured porosity, grain size, and bioturbation with tracer particles to relate to acoustic properties. Infaunal effects on post-storm sediment structure may be important to consider for acoustic mapping of reconsolidating sediment in shallow coastal areas.

Impact of seawater Mg2+/Ca2+ on Mg/Ca of asterozoan skeleton – Evidence from culturing and the fossil record

Skeletal Mg/Ca in echinoderms is thought to be related to ambient seawater Mg2+/Ca2+ ratio, which prompts the use of well-preserved fossil echinoderms as paleoseawater Mg2+/Ca2+ proxies. Nonetheless, experimental studies testing the effect of seawater Mg2+/Ca2+ ratio on echinoderm skeleton are limited to one echinoderm class, i.e., sea urchins (echinoids). Here, we investigated the effect of decreased seawater Mg2+/Ca2+ ratio on skeletal composition (Mg/Ca ratio) of a sea star Asterias rubens and a brittle star Ophiocomina nigra. Specimens were tagged with manganese and then cultured under three different Mg2+/Ca2+ molar ratios (~5.2, ~2.5, ~1.5 mol/mol) in order to simulate variations of ambient seawater Mg2+/Ca2+ ratio that existed throughout the Phanerozoic. Decreased Mg2+/Ca2+ in seawater did not affect the respiration rates or inhibit calcification of sea stars, which suggests that they were not significantly stressed by the treatment. It did, however, clearly affect growth and mortality in brittle stars, for which reliable geochemical data could not be obtained. Under decreased seawater Mg2+/Ca2+ sea stars produced a skeleton with decreased Mg/Ca ratio. This is consistent with the hypothesis that the skeletal chemistry in echinoderms is influenced by seawater chemistry and, consequently, that fossil echinoderms may preserve a record of paleoseawater Mg2+/Ca2+. Although our data from well-preserved fossil sea stars from the Middle Jurassic and Miocene are consistent with low Mg2+/Ca2+ ratio of the Jurassic "calcite sea" and high Mg2+/Ca2+ ratio of the Miocene "aragonite sea", the accuracy of paleoseawater Mg2+/Ca2+ reconstructions from fossil echinoderms is limited by the fact that Mg partition coefficients vary significantly between different echinoderm species.

Classifying domain-specific text documents containing ambiguous keywords.

A keyword-based search of comprehensive databases such as PubMed may return irrelevant papers, especially if the keywords are used in multiple fields of study. In such cases, domain experts (curators) need to verify the results and remove the irrelevant articles. Automating this filtering process will save time, but it has to be done well enough to ensure few relevant papers are rejected and few irrelevant papers are accepted. A good solution would be fast, work with the limited amount of data freely available (full paper body may be missing), handle ambiguous keywords and be as domain-neutral as possible. In this paper, we evaluate a number of classification algorithms for identifying a domain-specific set of papers about echinoderm species and show that the resulting tool satisfies most of the abovementioned requirements. Echinoderms consist of a number of very different organisms, including brittle stars, sea stars (starfish), sea urchins and sea cucumbers. While their taxonomic identifiers are specific, the common names are used in many other contexts, creating ambiguity and making a keyword search prone to error. We try classifiers using Linear, Naïve Bayes, Nearest Neighbor, Tree, SVM, Bagging, AdaBoost and Neural Network learning models and compare their performance. We show how effective the resulting classifiers are in filtering irrelevant articles returned from PubMed. The methodology used is more dependent on the good selection of training data and is a practical solution that can be applied to other fields of study facing similar challenges.Database URL The code and date reported in this paper are freely available at http://xenbaseturbofrog.org/pub/Text-Topic-Classifier/

New data on brittle stars (Echinodermata: Ophiuroidea) from the Persian Gulf and Oman Sea, Iran

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 the 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.

Population structure, habitat preferences, feeding strategies, and diet of the brittle star Ophiopholis aculeata in nearshore and offshore habitats of the northwest Atlantic

AbstractOphiopholis aculeata is a ubiquitous brittle star (Echinodermata: Ophiuroidea) known to occur from the upper subtidal to the bathyal zone. Individuals from shallow inshore habitats (rhodolith beds and rock fields) and deeper offshore locations in eastern Canada were studied to assess the population structure, habitat selection, diet, and feeding strategies of this species through use of stable isotope analyses, gut contents, and laboratory experiments. Potential drivers of habitat selection such as depth, light conditions, body size, sex, intraspecific competition, and presence of predators were examined. This study highlighted variable population size structures and abundances as well as diversified food sources and feeding strategies (i.e., suspension and deposit feeding, scavenging, predation on live organisms, and even cannibalism) as a function of native depth and habitat. It also revealed that studies on the feeding biology of brittle stars must carefully consider sex and life stage as driving factors.

Interactive identification key to all brittle star families (Echinodermata; Ophiuroidea) leads to revised morphological descriptions

Ophiuroidea is the largest class among extant echinoderms, with over 2000 described species assigned to 33 families. Here, the first identification key to the recently revised classification was developed, and revised morphological descriptions were derived from it, expanding the previous short diagnoses. The key was built by analyzing internal and external skeletal characters of predominantly the type species of each family, including at least two mutually exclusive attributes per family. Various numeric and multistate characters were used to create a traditional as well as an interactive key using the DELTA and Xper software programs­. Illustrations (SEM and digital photos) are included in the key to facilitate the assessment of character states by users. Not only is it the first identification key to the families, according to the recently proposed new classification and the examined species, but this interactive key also assists users in understanding the family level taxonomy of brittle stars. The interactive key allows new characters and states to be added, when more species will have been analyzed, without the need to reconfigure the complete key (as may be necessary with conventional keys).