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Identifying cryptic species and juveniles in the Ophiuroidea has always been a challenge. However, post-larval developmental studies have the potential to uncover the identity of these cryptic species and juveniles, as they offer valuable information that is not often found in adults. Although the importance of studying growth series is well-known in ophiuroids, it is difficult to obtain and identify the juvenile stages. For this reason, most studies are restricted to brooding species and information is lacking for many species, including those of the genus Ophiocoma. In this study, a growth series was developed to show the main differences during the development of two similar species of Ophiocoma: Ophiocoma echinata and Ophiocoma trindadensis. Using morphometry and scanning electron microscopy, we describe in detail the juveniles, intermediate stage, and adults of O. echinata and O. trindadensis. Differences in the shape of the ventral arm plate and dorsalmost arm spines, the number of tentacle scales, and the presence of granules ventrally were highlighted in the separation and identification of juveniles of both species.

In contrast to synthetic materials, materials produced by organisms are formed in ambient conditions and with a limited selection of elements. Nevertheless, living organisms reveal elegant strategies for achieving specific functions, ranging from skeletal support to mastication, from sensors and defensive tools to optical function. Using state-of-the-art characterization techniques, we present a biostrategy for strengthening and toughening the otherwise brittle calcite optical lenses found in the brittlestar Ophiocoma wendtii. This intriguing process uses coherent nanoprecipitates to induce compressive stresses on the host matrix, functionally resembling the Guinier–Preston zones known in classical metallurgy. We believe that these calcitic nanoparticles, being rich in magnesium, segregate during or just after transformation from amorphous to crystalline phase, similarly to segregation behavior from a supersaturated quenched alloy.

The brittle stars of the family Ophiocomidae inhabit shallow waters and coral reefs of tropical regions. The species of Ophiocoma are difficult to identify due to high morphological variation, especially when different stages of development are observed. Here, based on morphological analyses, two Brazilian morphotypes of Ophiocoma were studied and characterized, Ophiocoma sp. NB (Northeastern Brazil) and Ophiocoma sp. TMV (Trindade and Martin Vaz Archipelago), and subsequently thoroughly analysed to confirm whether they were the same species or not. After the morphological studies, including external morphology, morphometry and microstructural characters, and analysis of molecular data, involving the 16S gene, it was concluded that Ophiocoma sp. NB and Ophiocoma sp. TMV do not correspond to the same species, the first being identified as Ophiocoma echinata (Lamarck, 1816) and the latter being a new species. This new species is characterized by two tentacle scales on the first arm segment and then one on all following segments, and the dorsalmost arm spines are robust and rounded, as wide as long or almost as wide as long.

The medicinal potential of marine invertebrates' bioactive components that may act as anti-COVID-19 demonstrated promising results. Ophiocoma dentata , which is common in the Red Sea, is one such source. Therefore, this study aimed to isolate a new compound from the brittle star, Ophiocoma dentata , and evaluate its efficacy as anti-COVID-19 in-silico and in-vitro. Standard procedures were followed in order to assess the isolated compound’s preliminary toxicity and anti-inflammatory properties. Computer virtual screening technology through molecular docking and ADMET studies was conducted as well as a new steroid derivative was isolated for the first time, named 5α-cholesta-4(27), 24-dien-3β, 23 β-diol. Investigation of the Anti-Covid-19 activity of the isolated compound using a Plaque reduction assay revealed 95% inhibition at a concentration of 5 ng/µl (12.48 µM). Moreover, this compound showed an IC 50 of 11,350 ± 1500 ng/ml against the normal fibroblast cells, indicating its safety. Interestingly, this compound exhibited anti-inflammatory activity with an IC 50 of 51.92 ± 0.03 μg/ml compared to a reference drug’s IC 50 of 53.64 ± 0.01 μg/ml, indicating that this compound is a potent anti-inflammatory. In silico data have proved that the isolated compound is a promising viral inhibitor against SARS-CoV2 and is thus recommended as a future nature preventive and curative antiviral drug.

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

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 StatementHere 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.

Photoreception and vision are fundamental aspects of animal sensory biology and ecology, but important gaps remain in our understanding of these processes in many species. The colour-changing brittle star Ophiocoma wendtii is iconic in vision research, speculatively possessing a unique whole-body visual system that incorporates information from nerve bundles underlying thousands of crystalline ‘microlenses’. The hypothesis that these might form a sophisticated compound eye-like system regulated by chromatophores has been extensively reiterated, with investigations into biomimetic optics and similar supposedly ‘visual’ structures in living and fossil taxa. However, no photoreceptors or visual behaviours have ever been identified. We present the first evidence of photoreceptor networks in three Ophiocoma species, both with and without microlenses and colour-changing behaviour. High-resolution microscopy, immunohistochemistry and synchrotron tomography demonstrate that putative photoreceptors cover the animals' oral, lateral and aboral surfaces, but are absent at the hypothesized focal points of the microlenses. The structural optics of these crystal ‘lenses’ are an exaptation and do not fulfil any apparent visual role. This contradicts previous studies, yet the photoreceptor network in Ophiocoma appears even more widespread than previously anticipated, both taxonomically and anatomically.

Echinoderms are one of the marine organisms that inhabit intertidal areas and have an important ecological role in marine ecosystems. The distribution of echinoderms in intertidal areas can give an idea of the condition of echinoderm communities. The purpose of this study is to determine the types of echinoderms and the abundance and dominance of echinoderms in Tombariri waters. North Sulawesi, Indonesia. The method used in this study is the quadratic transect method. The specimens obtained were preserved with 70% formalin and taken to the Marine Biology laboratory of the Faculty of Fisheries and Marine Sciences of UNSRAT for identification. Based on the results of the study, 12 species of echinoderms were identified, namely Linckia laevigata, Protoreaster nodosus, Archaster typicus, Echinometra mathaei, Echinothrix calamari's, Tripneustes gratilla, Holothuria atra, Holothuria scabra, Holothuria leucospilota, Ophiomastix annulosa, Ophiocoma erinaceus, and Ophiocoma scolopendrina. This type of Ophiocoma erinaceus has the highest density, which is 31.52%. Station 2 has a dominance value of 0.316 which is higher than stations 1 and 3.

Broadcast spawning, wherein gametes of both sexes are released for external fertilization, is a common mode of reproduction in marine organisms. Despite its importance in the life histories of many species, discovery of its timing is often based on chance observations. Here we report on the spawning of 2 shallow-water brittle stars in southern Taiwan known to have spawning induction, i.e. ovary homogenates induce spawning of conspecific males. The gonad index of both species exhibited an annual cycle with peaks from mid-spring to early summer. Successful induction of spawning in male Ophiocoma scolopendrina (Lamarck) inhabiting the intertidal zone was limited to low tides. After manipulating the depth of the water inhabited by brittle stars, we discovered that successful induction of spawning was not sensitive to the actual water level. However, males could consistently be induced to spawn at the time of low tides even when deprived of tidal influences in the laboratory. Therefore, an endogenous clock mechanism entrained by tide-associated phenomena may control the inductivity of mature male O. scolopendrina. Time of the day, i.e. day versus night, had no effect in this species. In O. dentata (Mueller and Troschel) living in the shallow subtidal zone in the same area, male induction was successful during both high and low tides and in both day and night.

Photosensitivity in most echinoderms has been attributed to ‘diffuse’ dermal receptors 1 , 2 , 3 . Here we report that certain single calcite crystals used by brittlestars for skeletal construction 4 , 5 are also a component of specialized photosensory organs, conceivably with the function of a compound eye. The analysis of arm ossicles in Ophiocoma 6 showed that in light-sensitive species, the periphery of the labyrinthic calcitic skeleton extends into a regular array of spherical microstructures that have a characteristic double-lens design. These structures are absent in light-indifferent species. Photolithographic experiments in which a photoresist film was illuminated through the lens array showed selective exposure of the photoresist under the lens centres. These results provide experimental evidence that the microlenses are optical elements that guide and focus the light inside the tissue. The estimated focal distance (4–7 µm below the lenses) coincides with the location of nerve bundles—the presumed primary photoreceptors. The lens array is designed to minimize spherical aberration and birefringence and to detect light from a particular direction. The optical performance is further optimized by phototropic chromatophores that regulate the dose of illumination reaching the receptors. These structures represent an example of a multifunctional biomaterial that fulfills both mechanical and optical functions.