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Structuring over many length scales is a design strategy widely used in Nature to create materials with unique functional properties. We here present a comprehensive analysis of an adult sea urchin spine, and in revealing a complex, hierarchical structure, show how Nature fabricates a material which diffracts as a single crystal of calcite and yet fractures as a glassy material. Each spine comprises a highly oriented array of Mg-calcite nanocrystals in which amorphous regions and macromolecules are embedded. It is postulated that this mesocrystalline structure forms via the crystallization of a dense array of amorphous calcium carbonate (ACC) precursor particles. A residual surface layer of ACC and/or macromolecules remains around the nanoparticle units which creates the mesocrystal structure and contributes to the conchoidal fracture behavior. Nature's demonstration of how crystallization of an amorphous precursor phase can create a crystalline material with remarkable properties therefore provides inspiration for a novel approach to the design and synthesis of synthetic composite materials.

This paper explores the ethical considerations surrounding research on echinoderms, a group of invertebrates that has recently garnered attention in the scientific community. The importance of responsible animal handling and the need for an ethical framework that encompasses echinoderms are emphasized. The 3Rs principle, advocating for the replacement of conscious living vertebrates with non-sentient material in research, is discussed as a guiding tool in current animal research practices. As invertebrates are generally classified as non-sentient animals, the replacement dimension tends to favor them as prevalent models in experimental research. While it currently lacks the means to assess the mental states of invertebrates, there is undeniable evidence of social behavior in many species, suggesting that a lack of interactions with these organisms could potentially adversely affect their wellbeing. In the last few years, considerable progress has been made in developing an ethical framework that takes invertebrates into account, particularly cephalopods, crustaceans, and echinoderms. In this context, we discuss the development of a broader conceptual framework of 5Rs that includes responsibility and respect, which may guide practices ensuring welfare in echinoderms, even in the absence of any particular normative.

Background Vasopressin/oxytocin (VP/OT)-type neuropeptides are well known for their roles as regulators of diuresis, reproductive physiology and social behaviour. However, our knowledge of their functions is largely based on findings from studies on vertebrates and selected protostomian invertebrates. Little is known about the roles of VP/OT-type neuropeptides in deuterostomian invertebrates, which are more closely related to vertebrates than protostomes. Results Here, we have identified and functionally characterised a VP/OT-type signalling system comprising the neuropeptide asterotocin and its cognate G-protein coupled receptor in the starfish (sea star) Asterias rubens , a deuterostomian invertebrate belonging to the phylum Echinodermata. Analysis of the distribution of asterotocin and the asterotocin receptor in A. rubens using mRNA in situ hybridisation and immunohistochemistry revealed expression in the central nervous system (radial nerve cords and circumoral nerve ring), the digestive system (including the cardiac stomach) and the body wall and associated appendages. Informed by the anatomy of asterotocin signalling, in vitro pharmacological experiments revealed that asterotocin acts as a muscle relaxant in starfish, contrasting with the myotropic actions of VP/OT-type neuropeptides in vertebrates. Furthermore, in vivo injection of asterotocin had a striking effect on starfish behaviour—triggering fictive feeding where eversion of the cardiac stomach and changes in body posture resemble the unusual extra-oral feeding behaviour of starfish. Conclusions We provide a comprehensive characterisation of VP/OT-type signalling in an echinoderm, including a detailed anatomical analysis of the expression of both the VP/OT-type neuropeptide asterotocin and its cognate receptor. Our discovery that asterotocin triggers fictive feeding in starfish provides important new evidence of an evolutionarily ancient role of VP/OT-type neuropeptides as regulators of feeding in animals.

Hypoxia is a mounting problem affecting the world's coastal waters, with severe consequences for marine life, including death and catastrophic changes. Hypoxia is forecast to increase owing to the combined effects of the continued spread of coastal eutrophication and global warming. A broad comparative analysis across a range of contrasting marine benthic organisms showed that hypoxia thresholds vary greatly across marine benthic organisms and that the conventional definition of 2 mg O₂/liter to designate waters as hypoxic is below the empirical sublethal and lethal O₂ thresholds for half of the species tested. These results imply that the number and area of coastal ecosystems affected by hypoxia and the future extent of hypoxia impacts on marine life have been generally underestimated.

The contribution of carbonate‐producing benthic organisms to the global marine carbon budget has been overlooked, the prevailing view being that calcium carbonate (CaCO 3 ) is predominantly produced and exported by marine plankton in the “biological pump.” Here, we provide the first estimation of the global contribution of echinoderms to the marine inorganic and organic carbon cycle, based on organism‐level measurements from species of the five echinoderm classes. Echinoderms' global CaCO 3 contribution amounts to ~0.861 Pg CaCO 3 /yr (0.102 Pg C/yr of inorganic carbon) as a production rate, and ~2.11 Pg CaCO 3 (0.25 Pg C of inorganic carbon) as a standing stock from the shelves, slopes, and abyssal depths. Echinoderm inorganic carbon production (0.102 Pg C/yr) is less than the global pelagic production (0.4–1.8 Pg C/yr) and similar to the estimates for carbonate shelves globally (0.024–0.120 Pg C/yr). Echinoderm CaCO 3 production per unit area is ~27.01 g CaCO 3 ·m −2 ·yr −1 (3.24 g C·m −2 ·yr −1 as inorganic carbon) on a global scale for all areas, with a standing stock of ~63.34 g CaCO 3 /m 2 (7.60 g C/m 2 as inorganic carbon), and ~7.97 g C/m 2 as organic carbon. The shelf production alone is 77.91 g CaCO 3 ·m −2 ·yr −1 (9.35 g C·m −2 ·yr −1 as inorganic carbon) in contrast to 2.05 g CaCO 3 ·m −2 ·yr −1 (0.24 g C·m −2 ·yr −1 as inorganic carbon) for the slope on a global scale. The biogeography of the CaCO 3 standing stocks of echinoderms showed strong latitudinal variability. More than 80% of the global CaCO 3 production from echinoderms occurs between 0 and 800 m, with the highest contribution attributed to the shelf and upper slope. We provide a global distribution of echinoderm populations in the context of global calcite saturation horizons, since undersaturated waters with respect to mineral phases are surfacing. This shallowing is a direct consequence of ocean acidification, and in some places it may reach the shelf and upper slope permanently, where the highest CaCO 3 standing stocks from echinoderms originate. These organism‐level data contribute substantially to the assessment of global carbonate inventories, which at present are poorly estimated. Additionally, it is desirable to include these benthic compartments in coupled global biogeochemical models representing the “biological pump” and its feedbacks, since at present all efforts have focused on pelagic processes, dominated by coccolithophores. The omission of the benthic processes from modeling will only diminish the understanding of elemental fluxes at large scales and any future prediction of climate change scenarios.

Marine invertebrates are a paraphyletic group that comprises more than 90% of all marine animal species. Lipids form the structural basis of cell membranes, are utilized as an energy reserve by all marine invertebrates, and are, therefore, considered important indicators of their ecology and biochemistry. The nutritional value of commercial invertebrates directly depends on their lipid composition. The lipid classes and fatty acids of marine invertebrates have been studied in detail, but data on their lipidomes (the profiles of all lipid molecules) remain very limited. To date, lipidomes or their parts are known only for a few species of mollusks, coral polyps, ascidians, jellyfish, sea anemones, sponges, sea stars, sea urchins, sea cucumbers, crabs, copepods, shrimp, and squid. This paper reviews various features of the lipid molecular species of these animals. The results of the application of the lipidomic approach in ecology, embryology, physiology, lipid biosynthesis, and in studies on the nutritional value of marine invertebrates are also discussed. The possible applications of lipidomics in the study of marine invertebrates are considered.

Stalked crinoids are uncommon fossils in the Cenozoic. This is particularly due to their continuous decline starting from the Late Cretaceous and gradual restriction to the deep-sea environment, which bears a fossil record bias. On the other hand, in recent times, new data have emerged documenting some relict populations of sea lilies in the shallow marine facies from the Cenozoic. Here, we report shallow-water occurrences of Eocene crinoids from Romania that are classified as Isselicrinus . The representatives of Isselicrinus reached their greatest palaeogeographic distribution during the Eocene in offshore environments, and the only find of these crinoids from shallow-water facies was from the Southern Hemisphere. Thus, our discovery documents the first Eocene shallow-water occurrence of this taxon from the Northern Hemisphere. This finding shows that isocrinids locally might have remained in shallow environments after the initiation of the so-called Mesozoic marine revolution (MMR).

Crinoids of the Order Comatulida are renowned for harboring a remarkable diversity of symbiotic organisms within echinoderms, including polychaetes, myzostomids, gastropods, crustaceans, brittle stars, or fish. Crinoids provide essential services to their symbionts, such as shelter, access to food resources, mating areas, nesting grounds, and nurseries. Symbionts within crinoids developed a variety of strategies, including foraging in the arm ambulacral grooves, preying upon other symbionts, living within galls, or accessing suspended food particles from the water column. In this work, we focused on the Great Reef of Toliara, where we collected specimens from seven crinoid species. Among the 84 crinoids examined, a total of 285 symbiotic  organisms were retrieved. These symbionts were either moving freely on their host or found within cysts. Stable isotope analyses of carbon and nitrogen for both hosts and symbionts have shown that (a) all crinoids shared a common trophic niche; (b) a community-based approach indicated that crinoids initiated trophic networks primarily based on suspended particulate organic matter; (c) non-specific symbionts exhibited consistent dietary preferences regardless of their host; (d) myzostomids inhabiting cysts were found to feed on their host tissues; and (e) free-moving symbionts displayed divergent trophic niches linked to their predatory, kleptoparasitic, or filter-feeding behaviors. This research underscores the role of crinoids, particularly comatulid species, as key components of tropical ecosystems in the Western Indian Ocean, inhabited by a hidden biodiversity with complex trophic networks. Their intricate morphology accommodates a range of feeding strategies, supporting a diverse associated fauna.

Matrikines (MKs) can be a rich source of functional nutrition components and additional therapy, thereby contributing to human health care and reducing the risk of developing serious diseases, including cancer. Currently, functionally active MKs as products of enzymatic transformation by matrix metalloproteinases (MMPs) are used for various biomedical purposes. Due to the absence of toxic side effects, low species specificity, relatively small size, and presence of various targets at the cell membranes, MKs often exhibit antitumor properties and, therefore, are promising agents for antitumor combination therapy. This review summarizes and analyzes the current data on the antitumor activity of MKs of different origins, discusses the problems and prospects for their therapeutic use, and evaluates the experimental results of studying the antitumor properties of MKs from different echinoderm species generated with the help of a complex of proteolytic enzymes from red king crab Paralithodes camtschatica. Special attention is paid to the analysis of possible mechanisms of the antitumor action of various functionally active MKs, products of the enzymatic activity of various MMPs, and the existing problems for their use in antitumor therapy.