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A water flow simulation device capable of adjusting flow velocity was designed in flow velocity range of 0–30 cm/s, with which an indoor experiment was conducted to simulate the movement and adhesive behaviors of different-sized Apostichopus japonicus under different flow velocities. Observation showed that, in slow flow (~5 cm/s), A. japonicus moved more distance than in still water, and hardly moved in the riptide (~30 cm/s); and the adhesive capacity of A. japonicus was related to the flow velocity and attachment time. A. japonicus were able to attach to the bottom after any attachment time in the slow flow, after 10 s in the medium flow (~15 cm/s), and after 60 s in the riptide (~30 cm/s). In addition, larger A. japonicus were stronger with adhesive ability than smaller ones. The transcriptome data showed that the expression of transient receptor potential cation channel subfamily A, member 1 (TRPA1) in the tube feet was increased significantly in a flowing water, but those in the tentacles and tube feet were not significantly changed. Fluorescence in-situ hybridization results showed that TRPA1 was expressed around the watervascular of tentacles, tube feet, body wall, and spines. Therefore, tube feet were important for sea cucumbers to keep themselves stable in relatively swift flow with adhesion ability.

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.

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.

Thermal perception is crucial for the fitness of marine invertebrates in intertidal and shallow waters. TRPA1 is a non-selective cation channel that belongs to the TRP family with pivotal roles in initiating signal transduction of thermal perception. We investigated expression patterns of SiTRPA1 in different tissues (tube feet, coelomocytes, gonads and gut) of the sea urchin Strongylocentrotus intermedius. SiTRPA1 expression patterns under acute and long-term temperature stimuli were investigated in tube feet of sea urchins. In the present study, the highest expression of SiTRPA1 was detected in tube feet of S. intermedius. The SiTRPA1 expression level in tube feet were significantly 235.7-fold, 450.0-fold and 3299.7-fold higher than those in the coelomocytes, gonads and gut (df = 3, F = 47.382, P < 0.001). Expression levels of SiTRPA1 in the other tissues (coelomocytes, gonads and gut) were not significantly different (df = 3, F = 47.382, P = 0.972). There was no significant difference of SiTRPA1 expression among all groups in the acute temperature increase experiment (df = 4, F = 0.25, P = 0.902). In the acute temperature decrease experiment, the expression of SiTRPA1 showed no significant difference among all groups (df = 4, F = 1.802, P = 0.205). With long-term exposure (6 weeks) to different temperatures, SiTRPA1 expression in the low temperature group (10°C) was significantly higher than those in the high temperature (20°C) and the control groups (15°C) (df = 2, F = 9.57, P = 0.014). There was no significant difference of SiTRPA1 expression between the high temperature (20°C) and the control temperature (15°C) groups (df = 2, F = 9.57, P = 0.808). These results indicate that SiTRPA1 expression significantly responds to long-term low temperature but not to acute temperature decrease. The present study provides new insights on the distribution and temporal expression of TRPA1 in marine invertebrates after acute and long-term temperature stimuli.

Sea urchins can easily navigate a wide range of challenging environments through the coordinated action of thousands of individually addressable rigid protective spines and flexible, reversibly adhesive tube feet. To investigate the potential implementation of these unusual locomotory appendages in a robotic context, we describe here the design, fabrication, and characterization of an untethered sea urchin-inspired robot driven by fluidic soft actuators. Due to the intrinsic design and fabrication difficulties in attempting to replicate the complexity of an adult sea urchin, we instead focused our attention on the development of a design that closely mimicked the body plan of an anatomically much simpler post-larval juvenile urchin. Consistent with its biological counterpart, our robotic prototype contained five flexible tube feet and ten rigid spines that could be independently driven by soft tripod actuators. Through the incorporation of permanent magnets into the distal ends of the flexible tube feet, our sea urchin-inspired robot could easily navigate across ferrous surfaces while adopting gaits and defensive postures that were surprisingly similar to its biological analog.

A new species of psychropotid holothurian, Psychropotes verrucicaudatus sp. nov., is described from "Jiaolong" Seamount in the South China Sea. A single specimen was taken by a manned submersible from soft bottom at a depth of 3615 m. Psychropotes verrucicaudatus has a violet body surrounded by a brim of fused tube feet, an unpaired dorsal appendage, 16 tentacles, and two rows of midventral tube feet. Both the dorsal skin and unpaired dorsal appendage are covered with conspicuous warts. The body-wall ossicles are crosses with three or four arms, and a short, central apophysis; in addition, a giant cross is present in each wart of the dorsal skin; the tentacles ossicles are rods with spines. The new species differs from its congeners in having a very short and warty dorsal appendage. We also provide the Genbank accession numbers of partial sequences of 16S rRNA and mitochondrial cytochrome oxidase subunit I gene. This is the first report of an elasipodid holothurian from the "Jiaolong" Seamount area.

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.

Background: Corticotropin-releasing hormone (CRH) mediates physiological responses to stressors in mammals by triggering pituitary secretion of adrenocorticotropic hormone, which stimulates adrenal release of cortisol. CRH belongs to a family of related neuropeptides that include sauvagine, urotensin-I, and urocortins in vertebrates and the diuretic hormone DH44 in insects, indicating that the evolutionary origin of this neuropeptide family can be traced to the common ancestor of the Bilateria. However, little is known about CRH-type neuropeptides in deuterostome invertebrates. Methods: Here, we used mass spectrometry, mRNA in situ hybridization, and immunohistochemistry to investigate the structure and expression of a CRH-type neuropeptide (ArCRH) in the starfish Asterias rubens (phylum Echinodermata). Results: ArCRH is a 40-residue peptide with N-terminal pyroglutamylation and C-terminal amidation, and it has a widespread pattern of expression in A. rubens. In the central nervous system comprising the circumoral nerve ring and 5 radial nerve cords, ArCRH-expressing cells and fibres were revealed in both the ectoneural region and the hyponeural region, which contains the cell bodies of motoneurons. Accordingly, ArCRH immunoreactivity was detected in innervation of the ampulla and podium of locomotory organs (tube feet), and ArCRH is the first neuropeptide to be identified as a marker for nerve fibres located in the muscle layer of these organs. ArCRH immunoreactivity was also revealed in protractile organs that mediate gas exchange (papulae), the apical muscle, and the digestive system. Conclusions: Our findings provide the first insights into CRH-type neuropeptide expression and function in the unique context of the pentaradially symmetrical body plan of an echinoderm.

Uncoupling protein 2 (UCP2) is a proton transporter located in the inner mitochondrial membrane,and inhibits the formation of adenosine triphosphate and reactive oxygen species by uncoupling oxidative phosphorylation. To provide a theoretical basis for the role of SiUCP2 in lipid metabolism,a 2 341-bp full-length cDNA of SiUCP2 from sea urchin Strongylocentrotus intermedius,which encodes 323 amino acids (predicted MW 36.11 kDa) was obtained,and the structure and function of the SiUCP2 gene and its expression at the mRNA and protein level were studied. SiUCP2 had high homology with UCP2 of other species. Expression of SiUCP2 was detected in the order of tube feet > gonads > coelomocytes > intestines. The expression level was the highest in prismatic larvae and lowest in the two-cell stage. Moreover,using in-situ hybridization,we found that SiUCP2 protein was expressed in the gonads and intestine. This study provided a theoretical basis for subsequent studies on the role of SiUCP2 and its regulatory mechanism in lipid metabolism,and for the improvement of gonad quality to obtain a higher economic value from sea urchins.

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.

The sea cucumber Apostichopus japonicus is an important aquaculture species in China because of its high nutritional and medicinal values. Gender, as a factor affecting the physiology of organisms, is always considered when improving the breeding efficiency of economically important animals. In the present study, protein expression profiles of the gonads and tube feet of male and female A. japonicus were investigated using a comparative proteomics approach. A set of 7499 proteins were identified, which covered a broad range of functions based on function annotations. A significant difference in protein expression profiles was observed between the gonads and tube feet of A. japonicus; gonads showed more apparent gender differences than tube feet. Moreover, the findings revealed that male A. japonicus had more specific functions and most of these functions were associated with energy consumption. Further analyses suggested that the regulation of ERK activity and the capacity of tyrosine production and virus immunity might be more powerful in male and female A. japonicus, respectively. Some candidate proteins were also recognized as potential targets for gender identification of A. japonicus. Overall, our study provides new insights into the understanding of molecular mechanisms underlying gender-based physiological differences in A. japonicus. Significance The current study aimed to reveal gender differences in the physiological characteristics of gonads and tube feet of the sea cucumber A. japonicus. To the best of our knowledge, this is the first proteomics study to analyze the differences in the protein expression profiles of external organs between male and female A. japonicus. The analysis revealed gender differences in the protein expression profiles of both gonads and tube feet of A. japonicus, and the gender differences in gonads were quite apparent. Moreover, according to the recognition of differentially expressed proteins and the enrichment analyses based on Kyoto Encyclopedia of Genes and Genomes, a draft view of how the physiological functions of A. japonicus were affected by gender was obtained. Male A. japonicus could have more specific functions related to energy consumption than females. The regulation of ERK activity and virus immunity might be more robust in male and female A. japonicus, respectively. Some candidate proteins were also recognized as potential targets for gender identification of A. japonicus. The findings presented here will improve the understanding of researchers about the molecular mechanisms underlying gender-based differences in A. japonicus and contribute to the meticulous breeding of A. japonicus.

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 starfishAsterias 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 preparationsin vitroand injection of these neuropeptidesin vivotriggers cardiac stomach retraction and inhibition of the onset of feeding inA. 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.

Somatostatin (SS) and allatostatin-C (ASTC) are structurally and evolutionarily related neuropeptides that act as inhibitory regulators of physiological processes in mammals and insects, respectively. Here, we report the first molecular and functional characterization of SS/ASTC-type signalling in a deuterostome invertebrate—the starfish Asterias rubens (phylum Echinodermata). Two SS/ASTC-type precursors were identified in A. rubens (ArSSP1 and ArSSP2) and the structures of neuropeptides derived from these proteins (ArSS1 and ArSS2) were analysed using mass spectrometry. Pharmacological characterization of three cloned A. rubens SS/ASTC-type receptors (ArSSR1–3) revealed that ArSS2, but not ArSS1, acts as a ligand for all three receptors. Analysis of ArSS2 expression in A. rubens using mRNA in situ hybridization and immunohistochemistry revealed stained cells/fibres in the central nervous system, the digestive system (e.g. cardiac stomach) and the body wall and its appendages (e.g. tube feet). Furthermore, in vitro pharmacological tests revealed that ArSS2 causes dose-dependent relaxation of tube foot and cardiac stomach preparations, while injection of ArSS2 in vivo causes partial eversion of the cardiac stomach. Our findings provide new insights into the molecular evolution of SS/ASTC-type signalling in the animal kingdom and reveal an ancient role of SS-type neuropeptides as inhibitory regulators of muscle contractility.

The radial water-vascular system of ophiuroids shows two kinds of hydraulic mechanism; one is concerned with the retraction and extension of the tube-feet, the other with their operation as effector-organs. At least in amphiurids, tube-feet are fully extended by pressure developed in the radial canal. The hydrostatic skeleton is defined by a spiral-fibre lattice, and may be further restrained by longitudinal fibres. Distortion of the lattice by serially-disposed muscles within the tube-foot permits reciprocal length change. In nematode worms and parts of some ophiuroid tube-feet, the lattice fibre angle allows a high degree of bending without buckling. A turgid latticebound tube-foot is stiff, but one restrained by longitudinal fibres is even more rigid. The load required to buckle a turgid Amphiura tube-foot 1.0 mm long is 3–5µN, and the tube-foot can itself exert approximately that force. Tube-feet of different shapes differ in their distribution of strength; some will yield first at the base, others at the tip. In this and other characters lie unsuspected adaptations to function.

The sea urchin test is composed of individual plates linked to each other in vertical and horizontal sutures either by connective tissue forming a flexible test or by skeletal processes and collagen fibres forming a rigid test. Musculature attached to the internal stereom of the test is restricted to: 1) ambulacral, peristomial and lantern muscles, e.g. in flexible sea urchins: 2) peristomial and lantern muscles, e.g. in rigid sea urchins with lantern and teeth; and 3) peristomial muscles, e.g. in rigid sea urchins without lantern and teeth. The internal muscles in the flexible test function as a pump. The lantern muscles function as a pump and take part in the feeding mechanism. The respiratory organs in sea urchins are specialized tube feet adapically situated on the test, and (’gills') orally situated on the test. One of the functions of the internal musculature in sea urchins is to pump oxygenated fluid from the respiratory organs to different parts of the body. In addition, the lantern muscles are part of the feeding mechanism.

Sea urchins have hundreds of specialized adhesive organs, the tube feet, which play a key role in locomotion, substrate attachment and food capture. Tube feet are composed by two functional units: a proximal cylindrical stem that is mobile and flexible, attached to a distal flattened disc that produces adhesive secretions. Oral tube feet discs possess a specialized duo-glandular epidermis that produces adhesive and de-adhesive secretions, enabling strong but reversible adhesion to the substrate. Due to the growing interest in biomimetic adhesives, several studies have been carried out to characterize sea urchin adhesives, and up to date, it has been shown that it is composed by proteins and glycans. The protein fraction has been the subject of several studies, that pin-pointed several adhesion-related candidates. Contrastingly, little is known about the glycans that compose sea urchin adhesives. This study aims at contributing to this topic by focusing on the characterization of the glycosidic fraction of the adhesive secreted by the sea urchin Paracentrotus lividus (Lamarck, 1816), using a battery of 22 lectins, applied to 3 complementary techniques. Our results show that five lectins label exclusively the disc adhesive epidermis and simultaneously the secreted adhesive, being, therefore, most likely relevant for sea urchin adhesion. In addition, it was possible to determine that the glycosidic fraction of the adhesive is composed by a high molecular weight glycoprotein containing N-acetylglucosamine oligomers.

The current increase in atmospheric CO2 concentration induces changes in the seawater carbonate system resulting in decreased pH and calcium carbonate saturation state, a phenomenon called ocean acidification (OA). OA has long been considered as a major threat to echinoderms because their extensive endoskeleton is made of high-magnesium calcite, one of the most soluble forms of calcium carbonate. Numerous studies addressed this question in sea urchins, but very few questioned the impact of OA on the sea star skeleton, although members of this taxon do not compensate their extracellular pH, contrary to most sea urchins. In the present study, adults of the common sea star, Asterias rubens from Kiel Fjord, a site experiencing natural acidification events exceeding pCO2 levels of 2500 µatm, were chronically exposed to different levels of simulated ocean acidification (pHT-SW 8.0, 7.4, 7.2), encompassing present and future conditions, for the duration of 109 days. Corrosion and mechanical properties of skeletal elements were studied using scanning electron microscopy, three-point bending tests as well as nanoindentation. The spines were significantly corroded at pHT-SW 7.4 and below while the ambulacral plates were only affected at pHT-SW 7.2. Nanoindentation of newly formed spines and ambulacral plates did not reveal significant CO2-induced differences in skeleton hardness or elasticity across treatments. Results of three-point bending tests revealed significantly reduced characteristic strength and fracture force of ambulacral plates from the median arm segment at pHT-SW 7.4 and below. These plates are those supporting the tube feet involved in the opening of bivalves during feeding and in the animal attachment to the substrate. Under reduced seawater pH, this might result in fracture of sea star plates during predation on mussel. The present results predict a possible impact of ocean acidification on the skeletal integrity of a marine keystone predator., info:eu-repo/semantics/inPress

In this paper, the effects of tube feet pores on the mechanical properties of Sea Urchin Skeleton (SUS) have been studied. The pore structure of drop-like Tripnenstes gratilla (a sea urchin) skeleton is characterized by Scanning Electron Microscopy (SEM). Based upon the data, the finite element method has been employed to analyze the Maximum Tensile Stress (MTS) of SUS models with different pore positions, accompanied by compressive tests on SUS-like ceramics. Results indicate that for a drop-like SUS, the MTS keeps a linear relationship with the maximum load applied on the SUS. More importantly, the mechanical performances of some perforated SUSs are better than their non-perforated counterparts due to their lower MTS values, e.g. the maximum load can thus be increased by 35% when the pore is perforated at −10°. The strengthening is attributed to the introduced pore that causes the redistribution of stress and partly reduces the stress intensity on the original MTS position. By contrast, the pore only increases the MTS value of a spherical shell under isostatic pressure or unidirectional pressing. This is a strong hint that the drop-like shape of SUS has evolved to work with the tube feet pores to better protect their bodies.

The detection of light intensity and subsequent phototaxis are essential for the fitness of sea urchins in intertidal and shallow subtidal waters, where light intensity varies in accordance with the depth and other hydrographic conditions. The molecular basis of photoresponse, however, remains largely unknown. We compared the expression of SiOpsin4, SiPax6, and SiOpsin5 among tube feet, coelomocytes, gonads, and gut of the sea urchin Strongylocentrotus intermedius. All three genes showed the significantly highest expression in tube feet. To test whether r‐opsin genes (for example, Opsin4) and Pax6 in tube feet, rather than chaopsin genes (for example, Opsin5), are involved in the molecular responses to light intensity, we investigated the expression of Opsin4, Pax6, and Opsin5 among four light intensities. Both Opsin4 and Pax6 expressions were significantly higher in the sea urchins at 1,500 lx than at 100, 300, and 700 lx, indicating a co‐upregulation of Opsin4 and Pax6 expressions in sea urchins exposed to the high light intensity (for example, 1,500 lx). However, there was no significant difference of SiOpsin5 expression among the four light intensity groups. Consistent with our hypothesis, there was no significant difference in either Opsin4 or Pax6 expression between the two light intensity environments (low light intensity environment: 50–100 lx; high light intensity environment: 330–1400 lx). This indicates that positive phototaxis and negative phototaxis probably regulate the expression of Opsin4 and Pax6 to a similar level when sea urchins are exposed to the high and low light intensities, respectively. The present study provides new insights into the molecular basis of light intensity detection and subsequent phototaxis of eyeless species.

In this study, we performed comprehensive pathology examinations on 83 Tripneustes ventricosus from 11 locations on St. Kitts to build baseline data necessary for disease diagnosis in this species. Gross abnormalities were observed in 23/83 (28%) urchins and included spine loss, visceral hyperpigmentation, test discoloration, and test ulceration. Ciliates were the only protists identified in this study via examination of tissue wet mounts and histology, documented in 50/83 (60%) urchins. Microscopic observations associated with visibly abnormal status included muscle necrosis, test and appendage inflammation, appendage (tube feet, spines, and pedicellariae) degeneration, severe coelomocytosis, and generalized hypermelanosis. Enterocyte intranuclear inclusion bodies, microbial aggregates, nerve pigmentation, enteric pigmentation, integument-associated crustaceans, and encysted metazoan parasites were of uncertain pathological significance. The etiology for any lesion was not microscopically apparent, contrasting literature implicating common marine bacteria in urchin diseases. This study highlights the importance of histopathology in urchin disease investigations and facilitates the recognition of disease in T. ventricosus.

Mass mortality of the long line culture of the sea urchin Strongylocentrotus intermedius in summer, which is greatly associated with their disease, energy storage and resistant abilities, is the most serious problem for the development of the aquaculture. Here, a feeding experiment was conducted for ~ 9 weeks to investigate the survival, growth and gonadal development of small S. intermedius (~ 3 cm) fed either brown algae Sargassum horneri or Saccharina japonica. Subsequently, we assessed their resistant abilities via observing the behaviors of righting, tube feet extension and Aristotle's lantern reflex at both moderately elevated and acutely changed water temperatures. Sea urchins fed S. horneri showed significantly fewer diseased individuals and slower gonadal development than those fed S. japonica. Consistently, significantly greater Aristotle's lantern reflex occurred in sea urchins fed S. horneri at moderately elevated temperatures. These findings suggest that S. horneri has direct application potential as food for the long line culture of S. intermedius in summer because of the advantage in health, energy storage (avoid the energy loss caused by gonadal development at small body sizes) and resistance abilities. In comparison, sea urchins fed S. japonica outperformed those fed S. horneri for all experimental behaviors under the acutely changed water temperatures. These findings clearly suggest that S. intermedius fed S. japonica is more suitable for the areas with cold water mass in summer, because it can effectively avoid or reduce the negative impacts of acute changes of water temperature on sea urchins. The present study provides valuable information into the management of the long line culture of S. intermedius in summer.

Water motion, because of its potential to dislodge intertidal organisms, plays a crucial role in shaping marine communities as it creates available spaces suitable for interactions, settlement and colonization. To understand how water flow influences the behavioural ecology of benthic species such as echinoids, we investigated how the sea urchin Paracentrotus lividus (Lamark, 1816) can cope with increasing flow velocities through a biomechanical and behavioural approach. Whereas sea urchins maintained in static conditions for several weeks showed weak adhesive properties, they immediately reacted to increasing hydrodynamic forces. Sea urchins were dislodged at a flow velocity of about 70 cm s−1, with a few individuals enduring up to 90 cm s−1. This response was modulated by two behavioural strategies: (1) at low flow velocities, an escaping strategy characterized by fast upstream locomotion relying on tube feet; and (2) above a threshold flow, a streamlining strategy characterized by changes in overall shape and spines orientation, accompanied by a fast decrease of the animal's movement until complete immobility. Although the threshold at which the switch in behaviour occurs and the detachment velocities were both probably underestimated because individuals were aquarium-acclimatized, the behavioural sequence reported reveals how P. lividus can avoid or withstand rough weather conditions. From an ecological perspective, the occurrence of a range of water velocities too slow to dislodge sea urchins but sufficient to inhibit their active movement is relevant to understand how echinoids can structure benthic communities by controlling macroalgae development through their grazing activity., SCOPUS: ar.j, info:eu-repo/semantics/published

Background: Marine biological adhesives are a promising source of inspiration for biomedical and industrial applications. Nevertheless, natural adhesives and especially temporary adhesion systems are mostly unexplored. Sea stars are able to repeatedly attach and detach their hydraulic tube feet. This ability is based on a duo-gland system and, upon detachment, the adhesive material stays behind on the substrate as a 'footprint'. In recent years, characterization of sea star temporary adhesion has been focussed on the forcipulatid species Asterias rubens.Results: We investigated the temporary adhesion system in the distantly related valvatid species Asterina gibbosa. The morphology of tube feet was described using histological sections, transmission-, and scanning electron microscopy. Ultrastructural investigations revealed two adhesive gland cell types that both form electron-dense secretory granules with a more lucid outer rim and one de-adhesive gland cell type with homogenous granules. The footprints comprised a meshwork on top of a thin layer. This topography was consistently observed using various methods like scanning electron microscopy, 3D confocal interference microscopy, atomic force microscopy, and light microscopy with crystal violet staining. Additionally, we tested 24 commercially available lectins and two antibodies for their ability to label the adhesive epidermis and footprints. Out of 15 lectins labelling structures in the area of the duo-gland adhesive system, only one also labelled footprints indicating the presence of glycoconjugates with α-linked mannose in the secreted material.Conclusion: Despite the distant relationship between the two sea star species, the morphology of tube feet and topography of footprints in A. gibbosa shared many features with the previously described findings in A. rubens. These similarities might be due to the adaptation to a benthic life on rocky intertidal areas. Lectin- and immuno-labelling indicated similarities but also some differences in adhesive composition between the two species. Further research on the temporary adhesive of A. gibbosa will allow the identification of conserved motifs in sea star adhesion and might facilitate the development of biomimetic, reversible glues.

Movement in echinoderms is facilitated by the coordinated activity of thousands of individually addressable and reversibly adhesive tube feet. To investigate the potential applicability of these unique biological actuators as a locomotory structure for robotics applications, we describe here the design, fabrication, and evaluation of an elastomeric structural analogue. The synthetic tube feet were modeled as bistable deformable domes, containing an embedded magnet to facilitate the reversible attachment to ferromagnetic materials. Two unique robots were developed using the bistability of these domes - CircleBot, which is capable of rolling on ferrous surfaces using a pull and roll technique, and PlanarBot, which uses a programmed deflection direction in the domes to move in a plane.

Pedal peptide (PP) and orcokinin (OK) are related neuropeptides that were discovered in protostomian invertebrates (mollusks, arthropods). However, analysis of genome/transcriptome sequence data has revealed that PP/OK‐type neuropeptides also occur in a deuterostomian phylum—the echinoderms. Furthermore, a PP/OK‐type neuropeptide (starfish myorelaxant peptide, SMP) was recently identified as a muscle relaxant in the starfish Patiria pectinifera. Here mass spectrometry was used to identify five neuropeptides (ArPPLN1a‐e) derived from the SMP precursor (PP‐like neuropeptide precursor 1; ArPPLNP1) in the starfish Asterias rubens. Analysis of the expression of ArPPLNP1 and neuropeptides derived from this precursor in A. rubens using mRNA in situ hybridization and immunohistochemistry revealed a widespread pattern of expression, with labeled cells and/or processes present in the radial nerve cords, circumoral nerve ring, digestive system (e.g., cardiac stomach) and body wall‐associated muscles (e.g., apical muscle) and appendages (e.g., tube feet and papulae). Furthermore, our data provide the first evidence that neuropeptides are present in the lateral motor nerves and in nerve processes innervating interossicular muscles. In vitro pharmacological tests with SMP (ArPPLN1b) revealed that it causes dose‐dependent relaxation of apical muscle, tube foot and cardiac stomach preparations from A. rubens. Collectively, these anatomical and pharmacological data indicate that neuropeptides derived from ArPPLNP1 act as inhibitory neuromuscular transmitters in starfish, which contrasts with the myoexcitatory actions of PP/OK‐type neuropeptides in protostomian invertebrates. Thus, the divergence of deuterostomes and protostomes may have been accompanied by an inhibitory–excitatory transition in the roles of PP/OK‐type neuropeptides as regulators of muscle activity.

A new species of holothurian of the genusPsolusOken, 1815 is described.Psolus rufussp. nov. was found in the central Cantabrian slope (Bay of Biscay) at 1500 m depth. The new species is characterized by having: ovoid body, reddish colourin vivo; dorsal area enclosed in a complete test composed of imbricating scales; 10 triangular plates of the same size surrounding mouth; 10 oral tentacles; no dorsal papillae; tube feet in two rows in the ventrolateral radii but one single row in the medial third or the body; ossicles are big dorsal plates and small plates in the sole, which are smooth, irregular and perforated. The molecular study of the COI gene supports the morphological results, groupingP. rufussp. nov. together with other members of the genus. However, the new species is genetically distinct from the two groups (Antarctic and Canadian) of the available sequencedPsolusspecies. Furthermore, a key to thePsolusspecies of the north-eastern Atlantic Ocean is provided.