Interspecific Analysis of Sea Urchin Adhesive Composition Emphasizes Variability of Glycans Conjugated With Putative Adhesive Proteins

Sea urchins possess specialized adhesive organs, tube feet. Although initially believed to function as suckers, it is currently accepted that they rely on adhesive and de-adhesive secretions to attach and detach repeatedly from the substrate. Given the biotechnological potential of their strong reversible adhesive, sea urchins are under investigation to identify the protein and glycan molecules responsible for its surface coupling, cohesion and polymerization properties. However, this characterization has only focused on a single species, Paracentrotus lividus. To provide a broader insight into sea urchins adhesion, a comparative study was performed using four species belonging to different taxa and habitats: Diadema africanum, Arbacia lixula, Paracentrotus lividus and Sphaerechinus granularis. Their tube feet external morphology and histology was studied, together with the ultrastructure of their adhesive secretory granules. In addition, one antibody and five lectins were used on tube foot histological sections and extracts, and on adhesive footprints to detect the presence of adhesion-related (glyco)proteins like those present in P. lividus in other species. Results confirmed that the antibody raised against P. lividus Nectin labels the adhesive organs and footprints in all species. This result was further confirmed by a bioinformatic analysis of Nectin-like sequences in ten additional species, increasing the comparison to seven families and three orders. The five tested lectins (GSL II, WGA, STL, LEL, and SBA) demonstrated that there is high interspecific variability of the glycans involved in sea urchin adhesion. However, there seems to be more conservation among taxonomically closer species, like P. lividus and S. granularis. In these species, lectin histochemistry and lectin blots indicated the presence of high molecular weight putative adhesive glycoproteins bearing N-acetylglucosamine residues in the form of chitobiose in the adhesive epidermis and footprints. Our results emphasize a high selective pressure for conservation of functional domains in large putative cohesive proteins and highlight the importance of glycosylation in sea urchin adhesion with indications of taxonomy-related conservation of the conjugated glycans.

Perception of Dissolved Food-Related Compounds by the Sea Urchin Paracentrotus lividus (Echinodermata: Echinoidea)

Echinoid feeding biology is well known but their sluggish responses to chemical stimuli have turned them into inadequately worked in the field of chemoreception. Echinoid responses to chemical stimulation had allowed, so far, only qualitative analyses based on tube-feet activity, directional, or masticatory movements, and artificial agarose foods. Besides stimulation through plumes of dissolved organic compounds and response analysis based on tube-feet activity, we propose another method to chemically stimulate echinoids that allows for fast and unambiguous responses and thus, quantitative analyses. Small squared pieces of absorbent semi-synthetic cleaning cloths, soaked with specific chemical compounds (simulacra), such as water insoluble lipid oils, were deposited singly or concurrently with a blank on the aboral hemisphere of each sea urchin, allowing choice and eventual transport down to the mouth by tube feet and spines of one or both cloths. The responsiveness of Paracentrotus lividus was clearly dependent on its nutritional state. Well-fed sea urchins (maize whole grains) rarely responded, while the ones fed with less caloric rations (Kombu seaweed) responded faster and objectively. Stimulating sea urchin P. lividus with 41 different food-related compounds, such as carbohydrates, proteins, peptides and amino acids, oils and fatty acids, and purified chemicals related with some human basic tastes, it was possible to evidence a clear ability of this echinoid species to positively discriminate proteins, starches, and a very few oils. Perceived as incitants/stimulants we have only found among proteins gliadin (from wheat gluten) but not casein (from bovine milk), among polysaccharides starch but not laminarin (from kelp) or glycogen (from mussels), and among lipids only the fatty acid linolenic acid. Among tissues, Kombu alga flesh and mussel flesh were readily perceived as both incitant/stimulant but not Kombu and mussel extracts. Therefore, the combined results reported here provide evidence for P. lividus as an omnivorous species rather than a strictly herbivorous marine species. However, the restricted group of food-related compounds perceived by this species as incitants or suppressants and as stimulants or deterrents was shown to be remarkably related to other vertebrates whose kinship was confirmed by the sequencing of the genome of another plant-eater sea urchin.

The genome of an apodid holothuroid (Chiridota heheva) provides insights into its adaptation to deep-sea reducing environment

Cold seeps and hydrothermal vents are deep-sea reducing environments that are characterized by a lack of oxygen, photosynthesis-derived nutrients and a high concentration of reducing chemicals. Apodida is an order of deep-sea echinoderms lacking tube feet and complex respiratory trees, which are commonly found in holothurians. Chiridota heheva Pawson & Vance, 2004 (Apodida: Chiridotidae) is one of the few echinoderms that resides in deep-sea reducing environments. Unlike most cold seep and hydrothermal vent-dwelling animals, C. heheva does not survive by maintaining an epi- or endosymbiotic relationship with chemosynthetic microorganisms. The species acquires nutrients by extracting organic components from sediment detritus and suspended material. Here, we report a high-quality genome of C. heheva as a genomic reference for echinoderm adaptation to reducing environments. Chiridota heheva likely colonized its current habitats in the early Miocene. The expansion of the aerolysin-like protein family in C. heheva compared with other echinoderms might be involved in the disintegration of microbes during digestion, which in turn facilitates the species' adaptation to cold seep environments. Moreover, several hypoxia-related genes were subject to positive selection in the genome of C. heheva, which contributes to their adaptation to hypoxic environments.

Ancient role of sulfakinin/cholecystokinin-type signalling in inhibitory regulation of feeding processes revealed in an echinoderm

Sulfakinin (SK)/cholecystokinin (CCK)-type neuropeptides regulate feeding and digestion in protostomes (e.g. insects) and chordates. Here, we characterised SK/CCK-type signalling for the first time in a non-chordate deuterostome – the starfish Asterias rubens (phylum Echinodermata). In this species, two neuropeptides (ArSK/CCK1, ArSK/CCK2) derived from the precursor protein ArSK/CCKP act as ligands for an SK/CCK-type receptor (ArSK/CCKR) and these peptides/proteins are expressed in the nervous system, digestive system, tube feet, and body wall. Furthermore, ArSK/CCK1 and ArSK/CCK2 cause dose-dependent contraction of cardiac stomach, tube foot, and apical muscle preparations in vitro, and injection of these neuropeptides in vivo triggers cardiac stomach retraction and inhibition of the onset of feeding in A. rubens. Thus, an evolutionarily ancient role of SK/CCK-type neuropeptides as inhibitory regulators of feeding-related processes in the Bilateria has been conserved in the unusual and unique context of the extra-oral feeding behaviour and pentaradial body plan of an echinoderm.

Histologic Examination of a Sea Pig (Scotoplanes sp.) Using Bright Field Light Microscopy

Sea pigs (Scotoplanes spp.) are deep-sea dwelling sea cucumbers of the phylum Echinodermata, class Holothuroidea, and order Elasipodida. Few reports are available on the microscopic anatomy of these deep-sea animals. This study describes the histologic findings of two, wild, male and female Scotoplanes sp. collected from Monterey Bay, California. Microscopic findings were similar to other holothuroids, with a few notable exceptions. Sea pigs were bilaterally symmetrical with six pairs of greatly enlarged tube feet arising from the lateral body wall and oriented ventrally for walking. Neither a rete mirabile nor respiratory tree was identified, and the large tube feet may function in respiration. Dorsal papillae protrude from the bivium and are histologically similar to tube feet with a large, muscular water vascular canal in the center. There were 10 buccal tentacles, the epidermis of which was highly folded. Only a single gonad was present in each animal; both male and female had histologic evidence of active gametogenesis. In the male, a presumed protozoal cyst was identified in the aboral intestinal mucosa, and was histologically similar to previous reports of coccidians. This work provides control histology for future investigations of sea pigs and related animals using bright field microscopy.

A new species and comparative morphology of Philippine sea biscuits (Echinoidea: Clypeaster)

A new species of clypeasterid sea biscuit, Clypeaster brigitteae n. sp., is described from material collected in the Philippines at depths between 100 and 200 m. The new taxon increases the number of Clypeaster species recorded from the Philippines to nine, representing nearly a quarter of the world’s diversity of the genus. Other Philippine species include: C. annandalei Koehler, 1922; C. fervens Koehler, 1922; C. humilis (Leske, 1778); C. japonicus Döderlein, 1885; C. latissimus (Lamarck, 1816); C. pateriformis Mortensen, 1948; C. reticulatus (Linnaeus, 1758); and C. virescens Döderlein, 1885. Using type material where available, each of these species is compared and contrasted with C. brigitteae n. sp. in tables consisting of new data derived from general test shape and size, petal structure, food grooves, plate architecture, internal structure, and morphology of spines, pedicellariae, and tube feet.

Evolutionarily ancient role of cholecystokinin-type neuropeptide signalling as an inhibitory regulator of feeding-related processes revealed in an echinoderm

Cholecystokinin (CCK) / sulfakinin (SK)-type neuropeptides regulate feeding and digestion in chordates and protostomes (e.g. insects). Here we characterised CCK/SK-type signalling for the first time in a non-chordate deuterostome - the starfish Asterias rubens (phylum Echinodermata). In this species, two neuropeptides (ArCCK1, ArCCK2) derived from the precursor protein ArCCKP act as ligands for a CCK/SK-type receptor (ArCCKR) and are expressed in the nervous system, digestive system, tube feet and body wall. Furthermore, ArCCK1 and ArCCK2 cause dose-dependent contraction of cardiac stomach, tube foot and body wall apical muscle preparations in vitro and injection of these neuropeptides in vivo triggers cardiac stomach retraction and inhibition of the onset of feeding in A. rubens. Thus, an evolutionarily ancient role of CCK/SK-type neuropeptides as inhibitory regulators of feeding-related processes in the Bilateria has been conserved in the unusual and unique context of the extra-oral feeding behaviour and pentaradial body plan of an echinoderm.

Pentamera fonsecae n. sp. a new species of sea cucumber from the Pacific coast of Costa Rica (Holothuroidea: Dendrochirotida: Thyonidae)

Pentamera fonsecae n. sp. is described from seven specimens as a new species of Thyonidae from the Pacific coast of Costa Rica. It is distinguished from its congeners by having tables with ladder-shaped spires in the body wall, and tube feet with curved support tables of variable height and tables as those found in the body wall slightly smaller than those from the body wall. This species is distributed in Guanacaste, Costa Rica, from 28.5 to 40 m on muddy bottoms.