Tube Feet Research Articles

Role of Double Layers in the Formation of Conditions for a Polarization Phase Transition to the Superradiancestate in the Io Flux Tube

A possibility of the electron phase transition into cyclotron superradiance mode in a vicinity of the Io flux tube foot in the Jovian magnetosphere has been considered. A high power of cyclotron superradiance allows it to be considered as the main mechanism of decameter Jupiter radiation generation in the form of S-bursts. It was found that the downward electron beams emitted by Io are able to create electric double layers in the form of shock waves. Such waves, when moving along the flux tube, accelerate electrons in the magnetosphere. As a result, the temperature of the electron plasma component decreases considerably. The emerging upward electron beams create conditions favorable for the phase transition into the cyclotron superradiance mode to take place.

The structural and chemical basis of temporary adhesion in the sea star Asterina gibbosa.

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.

Gene expression across tissues, sex, and life stages in the sea urchin Tripneustes gratilla [Toxopneustidae, Odontophora, Camarodonta

The pan-tropical sea urchin Tripneustes gratilla is an ecologically and economically important shallow water algal grazer. The aquaculture of T. gratilla has spurred growing interest in the population biology of the species, and by extension the generation of more molecular resources. To this purpose, de novo transcriptomes of T. gratilla were generated for two adults, a male and a female, as well as for a cohort of approximately 1000 plutei larvae. Gene expression profiles of three adult tissue samples were quantified and compared. These samples were of gonadal tissue, the neural ring, and pooled tube feet and pedicellariae. Levels of shared and different gene expression between sexes, as well as across functional categories of interest, including the immune system, toxins, genes involved in fertilization, and sensory genes are highlighted. Differences in expression of isoforms between the sexes and Sex determining Region Y-related High Mobility Group box groups is observed. Additionally an expansion of the tumor suppressor DMBT1 is observed in T. gratilla when compared to the annotated genome of the sea urchin Strongylocentrotus purpuratus. The draft transcriptome of T. gratilla is presented here in order to facilitate more genomic level analysis of emerging model sea urchin systems.

Echinoderm-Inspired Tube Feet for Robust Robot Locomotion and Adhesion

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.

Molecular characterization and expression of NLRP10 in the antibacterial host defense of the sea cucumber (Apostichopus japonicus)

The nucleotide-binding oligomerization domain-like receptors (NOD-like receptors, NLRs) can regulate the innate immune process and is an important part of inflammatory body. In this study, we use transcriptome sequencing and the rapid amplification of cDNA ends approach to identify a novel NLRP gene in Apostichopus japonicus. We designated the gene as AjNLRP10. The full-length of AjNLRP10 is 4509 bp. The putative open reading frame comprising 3489 bp encodes a polypeptide with 1162 amino acid residues. The predicted molecular mass of AjNLRP10 is 132.87 kDa and its theoretical pI is 5.60. AjNLRP10 comprises a signal peptide with two Ig superfamily (IgSF) domains and a NACHT [NAIP (neuronal apoptosis inhibitory protein), CIITA (MHC class II transcription activator), HET-E (incompatibility locus protein from Podospora anserina) and TP1 (telomerase-associated protein)] domain. Spatial distribution expression analysis detected AjNLRP10 in all of the tissues tested, but with higher expression in the coelomocytes, medium expression in the intestine and respiratory tree, and slightly weaker expression in the body wall, tube feet, and longitudinal muscle. The expression levels of AjNLRP10 in the respiratory tree and intestines of sea cucumbers with skin ulceration syndrome were increased by 4-fold and 2.7-fold compared with those in healthy sea cucumbers, respectively. We investigated expression profiles of AjCasepase-1 (Cysteinyl aspartate specific proteinase-1) and AjMMP37 (mitochondrial protein-37) after AjNLRP10 knock-down and discovered that AjCasepase-1 was raised by 2.60-fold and AjMMP37 was raised by 3.84-fold. The study showed that AjNLRP10 has inhibitory effect in the immune process. In conclusion, this study showed that the AjNLRP10 protein found in the sea cucumber involved with the innate immune responses against bacterial infection. It has a similar structure and biological function to that in other organisms, where it appears to be involved with these results provide insights into the innate immune mechanism in the sea cucumber as well as suggesting new strategies for disease prevention, molecular therapy, and the development of novel drugs for sea cucumbers.

Crown-of-Thorns Sea Star Acanthaster cf. solaris Has Tissue-Characteristic Microbiomes with Potential Roles in Health and Reproduction.

ABSTRACTOutbreaks of coral-eating crown-of-thorns sea stars (CoTS; Acanthaster species complex) cause substantial coral loss; hence, there is considerable interest in developing prevention and control strategies. We characterized the microbiome of captive CoTS and assessed whether dysbiosis was evident in sea stars during a disease event. Most tissue types had a distinct microbiome. The exception was female gonads, in which the microbiomes were highly variable among individuals. Male gonads were dominated (>97% of reads) by a single Mollicutes-related operational taxonomic unit (OTU). Detailed phylogenetic and microscopy analysis demonstrated the presence of a novel Spiroplasma-related bacterium in the spermatogenic layer. Body wall samples had high relative abundance (43 to 64% of reads) of spirochetes, likely corresponding to subcuticular symbionts reported from many echinoderms. Tube feet were characterized by Hyphomonadaceae (24 to 55% of reads). Pyloric cecal microbiomes had high alpha diversity, comprising many taxa commonly found in gastrointestinal systems. The order Oceanospirillales (genera Endozoicomonas and Kistimonas) was detected in all tissues. A microbiome shift occurred in diseased individuals although differences between tissue types were retained. The relative abundance of spirochetes was significantly reduced in diseased individuals. Kistimonas was present in all diseased individuals and significantly associated with diseased tube feet, but its role in disease causation is unknown. While Arcobacter was significantly associated with diseased tissues and Vibrionaceae increased in diversity, no single OTU was detected in all diseased individuals, suggesting opportunistic proliferation of these taxa in this case. This study shows that CoTS have tissue-characteristic bacterial communities and identifies taxa that could play a role in reproduction and host health.IMPORTANCE Coral-eating crown-of-thorns sea stars (CoTS; Acanthaster species complex) are native to the Indo-Pacific, but during periodic population outbreaks they can reach extreme densities (>1,000 starfish per hectare) and function as a pest species. On the Great Barrier Reef, Australia, CoTS have long been considered one of the major contributors to coral loss. There has been significant investment in a targeted control program using lethal injection, and there is interest in developing additional and complementary technologies that can increase culling efficiencies. The biology of CoTS has been studied extensively, but little is known about their associated microbiome. This cultivation-independent analysis of the CoTS microbiome provides a baseline for future analyses targeting the functional role of symbionts, the identification of pathogens, or the development of reproduction manipulators.

Biomechanics and behaviour in the sea urchin Paracentrotus lividus (Lamarck, 1816) when facing gradually increasing water flows

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.

Formation of the ectodermal organs during the metamorphosis and definitive organogenesis in the holothurian Apostichopus japonicus

The fine structure of the ectodermal organs (epidermis and nervous system) in late doliolaria, pentactula, and 1-month-old juveniles of the holothurian Apostichopus japonicus was studied. The definitive structure of the epidermis is shown to start forming prior to metamorphosis. The cell types of late doliolaria epidermis are the same as those in adult holothurian epidermis, consisting of support, secretory, and granular cells. The rivet-like structures are also present already at this stage of development. The ciliary rings of late doliolaria represent ribbon-like aggregations of tall ciliary cells. The destruction of ciliary rings is due to the programmed death of ciliary cells, which are then utilized by mesenchymal cells. Changes to the epidermis during metamorphosis are linked to the sinking of the cells into the underlying extracellular matrix, resulting in the formation of the typical sunken epidermis of the body and appendages. The nervous system in late doliolaria consists of a nerve ring, five radial nerve cords, and tentacle and tube foot nerves. The nerve ring and the radial nerve cords represent epithelial tubes. First hyponeural cells appear in the mid-ventral nerve cord during the late doliolaria stage. In the rest of the nerve cords, the hyponeural part begins developing only after the settlement. Functioning of the adult nervous system in holothurians begins only after metamorphosis, following the complete loss of provisory organs and the switch to benthic life.

Biochemical, Anatomical, and Pharmacological Characterization of Calcitonin-Type Neuropeptides in Starfish: Discovery of an Ancient Role as Muscle Relaxants.

Calcitonin (CT) is a peptide hormone released by the thyroid gland that regulates blood Ca2+ levels in mammals. The CT gene is alternatively spliced, with one transcript encoding CT and another transcript encoding the CT-like neuropeptide calcitonin-gene related peptide (α-CGRP), which is a powerful vasodilator. Other CT-related peptides in vertebrates include adrenomedullin, amylin, and intermedin, which also act as smooth muscle relaxants. The evolutionary origin of CT-type peptides has been traced to the bilaterian common ancestor of protostomes and deuterostomes and a CT-like peptide (DH31) has been identified as a diuretic hormone in some insect species. However, little is known about the physiological roles of CT-type peptides in other invertebrates. Here we characterized a CT-type neuropeptide in a deuterostomian invertebrate—the starfish Asterias rubens (Phylum Echinodermata). A CT-type precursor cDNA (ArCTP) was sequenced and the predicted structure of the peptide (ArCT) derived from ArCTP was confirmed using mass spectrometry. The distribution of ArCTP mRNA and the ArCT peptide was investigated using in situ hybridization and immunohistochemistry, respectively, revealing stained cells/processes in the nervous system, digestive system, and muscular organs, including the apical muscle and tube feet. Investigation of the effects of synthetic ArCT on in vitro preparations of the apical muscle and tube feet revealed that it acts as a relaxant, causing dose-dependent reversal of acetylcholine-induced contraction. Furthermore, a muscle relaxant present in whole-animal extracts of another starfish species, Patiria pectinifera, was identified as an ortholog of ArCT and named PpCT. Consistent with the expression pattern of ArCTP in A. rubens, RT-qPCR revealed that in P. pectinifera the PpCT precursor transcript is more abundant in the radial nerve cords than in other tissues/organs analyzed. In conclusion, our findings indicate that the physiological action of CT-related peptides as muscle relaxants in vertebrates may reflect an evolutionarily ancient role of CT-type neuropeptides that can be traced back to the common ancestor of deuterostomes.

Identification and characterization of microRNAs from the tube foot in the sea urchin Strongylocentrotus intermedius

MicroRNAs (miRNAs) play critical roles in regulating many bio-processes of eukaryotes. The sea urchin Strongylocentrotus intermedius (an important fishery resource) is of great economic importance in Japan, North Korea, Russia, and China. In the current study, miRNAs of tube foot in S. intermedius were firstly identified and characterized. Data in this study can provide more genomic information for the further understanding of the complex regulation network in sea urchins and present a new way for monitoring the health status of cultured sea urchins.

Discovery and functional characterisation of a luqin-type neuropeptide signalling system in a deuterostome

Neuropeptides are diverse and evolutionarily ancient regulators of physiological/behavioural processes in animals. Here we have investigated the evolution and comparative physiology of luqin-type neuropeptide signalling, which has been characterised previously in protostomian invertebrates. Phylogenetic analysis indicates that luqin-type receptors and tachykinin-type receptors are paralogous and probably originated in a common ancestor of the Bilateria. In the deuterostomian lineage, luqin-type signalling has been lost in chordates but interestingly it has been retained in ambulacrarians. Therefore, here we characterised luqin-type signalling for the first time in an ambulacrarian – the starfish Asterias rubens (phylum Echinodermata). A luqin-like neuropeptide with a C-terminal RWamide motif (ArLQ; EEKTRFPKFMRW-NH2) was identified as the ligand for two luqin-type receptors in A. rubens, ArLQR1 and ArLQR2. Furthermore, analysis of the expression of the ArLQ precursor using mRNA in situ hybridisation revealed expression in the nervous system, digestive system and locomotory organs (tube feet) and in vitro pharmacology revealed that ArLQ causes dose-dependent relaxation of tube feet. Accordingly, previous studies have revealed that luqin-type signalling regulates feeding and locomotor activity in protostomes. In conclusion, our phylogenetic analysis combined with characterisation of luqin-type signalling in a deuterostome has provided new insights into neuropeptide evolution and function in the animal kingdom.

Identification of a novel antimicrobial peptide from the sea star Patiria pectinifera

Antimicrobial peptides (AMPs) are components of innate immunity found in many forms of life. However, there have been no reports of AMPs in sea star (Phylum Echinodermata). Here we report the isolation and characterization of a novel antimicrobial peptide from the coelomic epithelium extract of the sea star Patiria pectinifera. The isolated peptide comprises 38 amino acid residues, is cationic (pI 9.2), has four cysteine residues that form two disulfide bonds (C1-C3 and C2-C4), is amidated at the C-terminus, and is designated P. pectinifera cysteine-rich antimicrobial peptide (PpCrAMP). Synthetic PpCrAMP identical to the native peptide exhibited the most potent antimicrobial activity compared to analogs with different disulfide bond configurations. Expression analysis of PpCrAMP precursor transcripts revealed constitutive expression in the coelomic epithelium and tube feet of P. pectinifera. Analysis of genomic DNA and cDNA encoding the PpCrAMP precursor protein revealed that an intron splits the coding region of the mature peptide into a positively charged N-terminal domain and a C-terminal domain harboring four cysteine residues and a glycine for C-terminal amidation. No significant homology with other known AMPs was observed, while orthologs of PpCrAMP were found in other echinoderm species. These findings indicate that PpCrAMP is the prototype of a family a novel cysteine-rich AMPs that participate in mechanisms of innate immunity in echinoderms. Furthermore, the discovery of PpCrAMP may lead to the identification of related AMPs in vertebrates and protostome invertebrates.

Estimation of length of endotracheal tube insertion by foot length in newborns

Background: Intubation is a common procedure for neonates. This study was designed to determine whether the foot length (FL) can predict the depth of endotracheal (ET) tube insertion in newborns.Methods: This one year prospective cross-sectional study was done on 50 neonates admitted to NICU under the Department of Paediatrics, Rajarajeswari Medical College and Hospital, Bangalore from January 2016 to June 2017. The FL was measured and compared with the optimal depth of ET tube insertion. The data was analysed using SPSS version 20.0.Results: The mean FL was 7.42±0.75cms and mean optimal ET tube length was 7.70±0.71cm. The correlation between optimal ET tube length and foot length was noted in 70% of the babies and significant strong positive correlation was noted between optimal ET tube length and FL (r=0.780; p<0.001; R2=0.607). Significant differences were noted in mean FL and mean optimal depth of ET tube in term newborns (p=0.013) and those with normal weight (p=0.016).Conclusions: Foot length could be used as a simple and easy predictor in the estimation of endotracheal tube length in newborns.

Memory of direction of locomotion in sea urchins: effects of nerves on direction and activity of tube feet

Memory and learning in invertebrates with decentralized nervous systems is poorly understood and sea urchins are no exception. Following up on previous studies of locomotory direction in sea urchins, the regular sea urchin, Hemicentrotus pulcherrimus was used to examine whether they have directionality and ‘memory’ of direction in locomotion. Experiments were conducted in 2011–2013 on urchins collected from the subtidal rocky area off the Aburatsubo coast, Kanagawa, Japan. The sea urchins locomoted mainly with their tube feet. Individuals retained their directional locomotion in two successive trials separated by a resting period. This implies memory of the original direction and is termed “directional memory”. This memory was retained when the resting period was 5 min but disappeared when the period was extended to 10 min. Such directional memory was also observed in cutaway preparations in which the aboral one-third of the test was removed along with the viscera. The radial nerves (RNs) were severed in cutaway preparations to study their roles in memory and activities of the tube feet. The speed of locomotion was proportional to the total length of the RNs. When all RNs were separated from the nerve ring, the preparation continued to attach firmly to the substrate. When all RNs but one were cut at the midpoint, preparations locomoted keeping the ambulacrum with the uncut, longest RN forward. When all RNs were cut at the midpoint, directional memory was observed without the interference of the longest RN. A model in which each ambulacrum assumes one of four modes (leading, trailing, attached, or retracted) with its tube feet being controlled and coordinated by the RN, and where mode switching is caused by the mechanical pull of other ambulacra and or via the RN–ring system accounts for these findings.

Pharmacological Disruption of Sea Urchin Tube Foot Motility and Behavior.

The understanding of the molecular basis of sea urchin behavior and sensory and motor systems lags far behind that of many other animal species. To investigate whole-animal behavior pharmacologically, we first demonstrated that immersion in drug solution is an effective drug administration route for sea urchins, whereas oral drug administration was found to be ineffective. Although intracoelomic injection was found to be effective at administering drugs, it was also found that injection itself can disrupt normal sea urchin behavior. Using the drug immersion procedure, we demonstrate that sea urchin locomotion and the sea urchin righting response are inhibited in a dose-dependent manner by the phosphodiesterase inhibitor theophylline and the transient receptor potential channel inhibitor 2-aminoethoxydiphenyl borate. The sea urchin righting response was also inhibited by the nitric oxide synthase inhibitor N(G)-nitro-l-arginine methyl ester and the Ca2+ channel inhibitor diltiazem, which, along with theophylline and 2-aminoethoxydiphenyl borate, would all be expected to disrupt smooth muscle function, based on studies in other animals. In addition, the removal of extracellular Ca2+ also inhibited the righting response, whereas an inhibitor of intracellular Ca2+ release, thapsigargin, did not affect the righting response, indicating that extracellular Ca2+ rather than intracellular Ca2+ stores are required for righting.

Non-destructive tissue sampling and the use of PCR-RFLPs in two edible sea cucumbers from the north-eastern Atlantic, Holothuria mammata Grube, 1840 and H. sanctori Delle Chiaje, 1823 (Echinodermata: Holothuroidea)

Historically, the harvest and consumption of sea cucumbers have been largely restricted to Asian countries. Recently, however, the western world has witnessed a rapid growth of holothurian-related industries, and Holothuria mammata Grube, 1840 and H. sanctori Delle Chiaje, 1823 are now being commercially harvested in European and North African countries. The identification of holothurian species tends to be difficult and time-consuming, and in many cases needs experienced taxonomists. We suggest a simple non-destructive DNA sampling, using tube feet or oral tentacles from these two species. We also describe a simple and fast method of diagnose based on polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) using restriction nuclease Sau3AI on 16S rRNA fragments. The use of RFLPs to rapidly and inexpensively identify species with no need for taxonomical or genetic expertise could prove a valuable asset for conservation and fishery purposes targeting commercially harvested animals such as the holothurians in the north-east Atlantic and the Mediterranean Sea.

Functional characterization of a second pedal peptide/orcokinin-type neuropeptide signaling system in the starfish Asterias rubens.

Molluscan pedal peptides (PPs) and arthropod orcokinins (OKs) are prototypes of a family of neuropeptides that have been identified in several phyla. Recently, starfish myorelaxant peptide (SMP) was identified as a PP/OK‐type neuropeptide in the starfish Patiria pectinifera (phylum Echinodermata). Furthermore, analysis of transcriptome sequence data from the starfish Asterias rubens revealed two PP/OK‐type precursors: an SMP‐type precursor (A. rubens PP‐like neuropeptide precursor 1; ArPPLNP1) and a second precursor (ArPPLNP2). We reported previously a detailed analysis of ArPPLNP1 expression in A. rubens and here we report the first functional characterization ArPPLNP2‐derived neuropeptides. Sequencing of a cDNA encoding ArPPLNP2 revealed that it comprises eleven related neuropeptides (ArPPLN2a‐k), the structures of several of which were confirmed using mass spectrometry. Analysis of the expression of ArPPLNP2 and neuropeptides derived from this precursor using mRNA in situ hybridization and immunohistochemistry revealed a widespread distribution, including expression in radial nerve cords, circumoral nerve ring, digestive system, tube feet and innervation of interossicular muscles. In vitro pharmacology revealed that the ArPPLNP2‐derived neuropeptide ArPPLN2h has no effect on the contractility of tube feet or the body wall‐associated apical muscle, contrasting with the relaxing effect of ArPPLN1b (ArSMP) on these preparations. ArPPLN2h does, however, cause dose‐dependent relaxation of cardiac stomach preparations, with greater potency/efficacy than ArPPLN1b and with similar potency/efficacy to the SALMFamide neuropeptide S2. In conclusion, there are similarities in the expression patterns of ArPPLNP1 and ArPPLNP2 but our data also indicate specialization in the roles of neuropeptides derived from these two PP/OK‐type precursors in starfish.

Water vascular system architecture in an Ordovician ophiuroid.

Understanding the water vascular system (WVS) in early fossil echinoderms is critical to elucidating the evolution of this system in extant forms. Here we present the first report of the internal morphology of the water vascular system of a stem ophiuroid. The radial canals are internal to the arm, but protected dorsally by a plate separate to the ambulacrals. The canals zig-zag with no evidence of constrictions, corresponding to sphincters, which control pairs of tube feet in extant ophiuroids. The morphology suggests that the unpaired tube feet must have operated individually, and relied on the elasticity of the radial canals, lateral valves and tube foot musculature alone for extension and retraction. This arrangement differs radically from that in extant ophiuroids, revealing a previously unknown Palaeozoic configuration.

Influence of body size on tube feet morphology and attachment capacity in the sea urchin Holopneustes purpurascens (Temnopleuridae)

Body size is an important feature of how species interact with their environment, and can influence predation risk, requirements and type of diet consumed, habitat suitability, and susceptibility to environmental pressures. Echinoderms, such as sea urchins, often inhabit areas subjected to wave disturbance and tidal flow, and are able to withstand such forces using a unique method of gel adhesion that allows individuals to adhere to the substratum in these hostile environments. We assessed attachment capacity in relation to body size for the Australian sea urchin Holopneustes purpurascens, which lives enmeshed in two distinct types of algae, attached by tube feet. Relationships between the tube feet, which occur around the entire body, and body size were examined. The number of tube feet, tube foot disc surface area, and fully attached footprints increased as individual body size increased. Our results also demonstrated that all tube feet were functionally adhesive, enabling full enmeshment in the host alga. Our findings indicate that the attachment capacity is positively correlated with body size and that H. purpurascens display both morphological and adhesive characteristics that enable a size-driven host plant distribution. This change in attachment capacity may play an important role in the ontogenetic shift observed in H. purpurascens, with future research suggested to explore the relationship between attachment capacity and adhesive tenacity within this species and other echinoderms.

A taxonomic revision of the genus Apostichopus (Holothuroidea: Stichopodidae) from Japan.

Complete redescriptions of sea cucumbers in the genus Apostichopus Liao, 1980 are provided using the type specimens and specimens deposited in the National Museum of Nature and Science, Tsukuba, Japan. The genus consists of A. armatus (Selenka, 1867) and A. japonicus (Selenka, 1867), which can be distinguished by some spicules in the dorsal body wall; the rim of reduced table spicules in A. armatus is spinous, while that in A. japonicus is smooth. Spicules from the tentacles, papillae, tube feet, and cloaca are similar for both species.