Water Vascular System Research Articles

Feeding postures as indicators of mutable collagenous tissue in extinct echinoderms.

Echinoderms are a diverse phylum with a rich fossil record. The five extant classes of echinoderms are characterised by a pentameral (or pseudo-pentameral) symmetry, a water vascular system, a mesodermal skeleton of calcite stereom, and Mutable Collagenous Tissue (MCT), a unique type of connective tissue. Difficulties in tracing the geologic history of these traits complicates phylogenetic analyses of echinoderms. We present evidence herein of MCT in an extinct class of echinoderms, the Blastoidea. Blastoids have composite hair-like structures, brachioles, which formed a feeding filtration fan. Rare specimens from the Devonian of Germany demonstrate the presence of MCT by preserving brachioles as long rigid structures making a feeding fan with MCT in a rigid state. Specimens show brachioles in different configurations in the same specimen, which may indicate nervous control of MCT in individual brachioles. Other specimens appear to indicate the transition of MCT from a rigid to a compliant state as rigid brachioles begin to curve. Still other specimens show a majority of brachioles as limp hair-like structures swept by currents while a minority of brachioles remain rigid. These remarkable specimens could capture MCT transitioning from its rigid to compliant states in individual specimens indicating rapid burial and preservation.

Endocrine regulation of reproductive biology in echinoderms: An evolutionary perspective from closest marine invertebrate relatives to chordates

Echinoderms are a phylum of invertebrate deuterostomes, which contain echinoids, asteroids, holothuroids, crinoids, and ophiuroids. Echinoderms have special evolutionary position and unique characteristics, including pentamerous radial body structure, elaborate calcareous endoskeletons, and versatile water vascular system. Echinoderms exhibit extraordinarily diverse reproductive modes: asexual reproduction, sexual reproduction, sexual reversal, etc. Endocrine regulation plays important well-known roles in sex differentiation, gonadal development and maturation, gametogenesis, and reproductive behavior in vertebrates. However, the entire picture of reproductive endocrinology in echinoderms as an evolutionary model of the closest marine invertebrate relatives to chordates has not been revealed. Here, we reviewed previous and recent research progress on reproductive endocrinology in echinoderms, mainly including two sections: Sex steroids in echinoderms and neuropeptide regulation in echinoderm reproduction. This review introduces a variety of endocrine regulatory mechanisms in reproductive biology of echinoderms. It discusses the vertebrate-like sex steroids, putative steroidogenic pathway and metabolism, and reproduction-related neuropeptides. The review will provide a deeper understanding about endocrine regulatory mechanisms of gonadal development in lower deuterostomes and the application of endocrine control in economic echinoderm species in aquaculture.

Skeletal elements controlled soft-tissue preservation in echinoderms from the Early Ordovician Fezouata Biota

Exceptional fossils preserve non-biomineralized tissues in the geological record and provide crucial information on the evolution of life on Earth. Exceptionally preserved fossils are rarely discovered complete, challenging their morphological description and their palaeontological interpretation. Although decay experiments reconstructing degradation sequences in modern animals are necessary to better understand taphonomic processes involved in exceptional preservation, their applicability to some enigmatic and/or extinct fossil taxa remains limited. Here, based on a representative sample of 423 specimens collected from a single stratigraphic level from the Early Ordovician Fezouata Biota, we reconstruct the degradation sequence of both skeletal remains and soft tissues of stylophorans, an extinct clade of echinoderms. The rare preservation of the water vascular system can be explained by the rapid post-mortem opening of the cover plates resulting from the fast decay of associated muscles and the action of ligaments. In contrast, the proximal aulacophore and associated stylocone formed a particularly decay-resistant closed module, thus favouring the preferential preservation of included soft parts (fore-gut). The non-random location and frequency of pyritised intra-skeletal structures strongly suggest that skeletal elements dictated the preservation of underlying soft parts. As such, taphonomic investigations should not only focus on the environment surrounding a decaying animal, but also on the different environments created within a particular carcass.

A Bionic Starfish Adsorption Crawling Soft Robot

A variety of soft wall-climbing robots have been developed that can move in certain patterns. Most of these soft robots can only move on conventional surfaces and lack adaptability to complex surfaces. Improving the adaptability of soft robots on complex surfaces is still a challenging problem. To this end, we study the layered structure of the starfish tube foot and the valve flap structure in the water vascular system, and use an ultrasonic stress detector to study the stiffness distribution of the arm structure. Inspired by the motion of the starfish, we present a bionic soft wall-climbing robot, which is driven by two groups of pneumatic feet and achieves body bending through active adaptation layers. We design the structure of the foot to flex to provide driving force, and there are suction cups at the end of the foot to provide suction. The soft foot has a simple structure design, adapts to a variety of surfaces, and does not damage the surface of the substrate. Variable stiffness layers achieve stiffness changes by the principle of line blocking. The Central Pattern Generator theory is introduced to coordinately control the multiple feet of the robot. After experiments, we verify the adaptability of the soft robot to curved surfaces. The research may provide a reference for the design and development of crawling soft robots on complex surfaces.

Analysis of the P. lividus sea urchin genome highlights contrasting trends of genomic and regulatory evolution in deuterostomes

Sea urchins are emblematic models in developmental biology and display several characteristics that set them apart from other deuterostomes. To uncover the genomic cues that may underlie these specificities, we generated a chromosome-scale genome assembly for the sea urchin Paracentrotus lividus and an extensive gene expression and epigenetic profiles of its embryonic development. We found that, unlike vertebrates, sea urchins retained ancestral chromosomal linkages but underwent very fast intrachromosomal gene order mixing. We identified a burst of gene duplication in the echinoid lineage and showed that some of these expanded genes have been recruited in novel structures (water vascular system, Aristotle's lantern, and skeletogenic micromere lineage). Finally, we identified gene-regulatory modules conserved between sea urchins and chordates. Our results suggest that gene-regulatory networks controlling development can be conserved despite extensive gene order rearrangement.

About the Cover

Next article FreeAbout the CoverPDFPDF PLUSFull Text Add to favoritesDownload CitationTrack CitationsPermissionsReprints Share onFacebookTwitterLinked InRedditEmailQR Code SectionsMoreA defining feature of echinoderms is their five-fold symmetry, which arises during the metamorphosis of a bilaterally symmetrical larva. During echinoderm metamorphosis, the coelomic cavities undergo an elaborate transformation from early mesodermal pouches to a complex system of tubes and rings that make up the numerous internal components of the animal. In this issue (pp. 283–298), H. C. Sweet and several undergraduate research students (G. Azriel, N. Jaff, J. Moser, T. A. Riola, C. Ideman, M. Barton, J. Nelson, and M. M. Lenhart) demonstrate the origin of the coelomic structures and their morphogenesis in the vitellaria larva of the brittle star Ophioplocus esmarki. Many of the structures first form when the archenteron becomes subdivided into an unpaired axocoel, hydrocoel, somatocoel, and stomach rudiment. The right somatocoel and part of the left somatocoel originate as bilateral invaginations of the larval ectoderm. This supports the findings of others that ectodermal invagination of the somatocoels is an unusual feature of brittle star development. Confocal microscopy and 3D modeling were used to document the later morphogenesis of the coelomic cavities as they form juvenile structures with five-fold symmetry.The cover image demonstrates the complex structure of the vitellaria larva. The image shows the color-coded coelomic cavities superimposed with an image of the skeleton and an outline of body of the vitellaria larva. At this stage, the outer ectoderm has ciliary bands on raised ridges that are used for swimming (grayscale outline), but most of the internal structures are patterned in five-fold symmetry with the axial complex near the anterior end (top). Coelomic structures include the water vascular system derived from the hydrocoel (yellow), hypogastric coelom derived from the left somatocoel (purple), genital coelom (peach) derived from the left somatocoel, epigastric coelom derived from the right somatocoel (magenta), pericardial coelom (green), axial coelom (orange), and pore canal (red). The juvenile skeletal plates form adjacent to the coelomic structures and the overlying ectoderm. The image was generated with confocal microscopy, polarized light imaging, and image colorizing and processing in GIMP and Fiji.Credits: Photo, Hyla C. Sweet; cover design, Olivia Kinker. Next article DetailsFiguresReferencesCited by The Biological Bulletin Volume 243, Number 3December 2022 Published in association with the Marine Biological Laboratory Article DOIhttps://doi.org/10.1086/724434 © 2022 The University of Chicago. All rights reserved.PDF download Crossref reports no articles citing this article.

The pentameric hydrocoel lobes organize adult pentameral structures in a sea cucumber, Apostichopus japonicus

Despite being one of the bilaterians, the body plan of echinoderms shifts from bilateral symmetry to five-fold radial, or pentaradial symmetry during embryogenesis or their metamorphosis. While the clarification of the developmental mechanism behind this transition will be a basis for understanding their unique body plan evolution, it is still poorly understood. With this regard, the hydrocoel, a mesodermal coelom formed on the left side of bilateral larva, would be a clue for understanding the mechanism as it is the first pentaradial structure that appears before metamorphosis and develops into the water vascular system of adults. By analyzing the development of a sea cucumber, Apostichopus japonicus, we found that the hydrocoel expresses genes related in muscle and neural formation such as myosin heavy chain, tropomyosin, soxC, and elav, implying that cells of the hydrocoel contributes to muscle and neural structures in the adult. Furthermore, ablation of one of the hydrocoel lobes led to incomplete development of adult pentameral structures. The ablation of primary hydrocoel lobes resulted in the reduction in tentacles and the ablation of secondary hydrocoel lobes resulted in the reduction in water vascular canals and nerve cords. Our findings suggest that the hydrocoel lobes may serve as a potential organizing center for establishing the pentaradial body plan in echinoderms.

Scope for Developmental Plasticity of Feeding Larvae of a Holothuroid, Contrasted with Other Echinoderm Larvae.

AbstractFeeding larvae of echinoderms appear to differ in scope for adaptive developmental plasticity in response to food. Extension of the ciliary band on narrow arms supported by skeletal rods, as in echinoid and ophiuroid larvae, may enable a greater increase in maximum clearance rate per cell added, conferring greater advantages from developing longer ciliary bands when food is scarce. Formation of the juvenile mouth and water vascular system at a new site, as in echinoid and asteroid larvae, permits extensive growth of the juvenile rudiment during larval feeding, with advantages from earlier or more growth of the rudiment when food is abundant. In contrast, plasticity in storage of nutrients is unrelated to the form of the ciliary band or the site of formation of the juvenile's mouth. Feeding larvae (auriculariae) of holothuroids lack arms supported by skeletal rods and formation of the mouth at a new site but as a unique feature store nutrients in hyaline spheres. In this study, more food for auriculariae of Apostichopus californicus resulted in juveniles (pentactulae) with longer and wider bodies and larger hyaline spheres, but effects of food supply on the size of most body parts of auriculariae were small. Auriculariae with more food developed relatively larger stomachs and larger posterior hyaline spheres, indications of greater nutrient storage. Auriculariae with less food developed relatively wider mouths and differed in some exterior dimensions, which might enhance the capture of food. Plasticity is limited in rudiment development and perhaps in structures for feeding, but plasticity in nutrient storage can provide advantageous compromises between duration of growth as a feeding larva and the condition of juveniles formed at metamorphosis.

Psolidium bathygalego nom. nov. (Echinodermata, Holothuroidea) from bathyal bottoms of Galicia (NW Iberian Peninsula).

It is proposed to name the Atlantic holothuria Psolidium complanatum Cherbonnier, 1969, whose denomination is already occupied by Psolidium complanatum (Semper, 1867) from the Philippines, as Psolidium bathygalego nom. nov. 843 specimens of Psolidium bathygalego nom. nov., collected between 417 and 1191 m deep in the NW and W of Galicia and in the Galicia Bank, were studied. A detailed description of the external and internal anatomy of Psolidium bathygalego nom. nov. is made by studying the ossicles and the skeletal structure by means of scanning electron microscopy (SEM) as well as the introvert, calcareous ring, retractor muscles, water-vascular system, digestive system, respiratory trees, and reproductive system by means of micro-computed tomography (micro-CT). The habitat, feeding system, and geographical distribution of Psolidium bathygalego nom. nov. are also described.

Soil Bioassay for Detecting Magnaporthiopsis maydis Infestation Using a Hyper Susceptible Maize Hybrid.

Magnaporthiopsis maydis is the causal agent of severe maize late wilt disease. Disease outbreak occurs at the maize flowering and fruit development stage, leading to the plugging of the plant’s water vascular system, resulting in dehydration and collapse of the infected host plant. The pathogen is borne by alternative hosts, infected seeds, soil, and plant residues and gradually spreads to new areas and new countries. However, no soil assay is available today that can detect M. maydis infestation and study its prevalence. We recently developed a molecular quantitative Real-Time PCR (qPCR) method enabling the detection of the M. maydis DNA in plant tissues. Despite the technique’s high sensitivity, the direct examination of soil samples can be inconsistent. To face this challenge, the current work demonstrates the use of a soil bioassay involving the cultivation of a hyper-susceptible maize genotype (Megaton cultivar, Hazera Seeds Ltd., Berurim MP Shikmim, Israel) on inspected soils. The use of Megaton cv. may facilitate pathogen establishment and spread inside the plant’s tissues, and ease the isolation and enrichment of the pathogen from the soil. Indeed, this cultivar suffers from severe dehydration sudden death when grown in an infested field. The qPCR method was able to accurately and consistently identify and quantify the pathogen’s DNA in an in vitro seed assay after seven days, and in growth-chamber potted plants at as early as three weeks. These results now enable the use of this highly susceptible testing plant to validate the presence of the maize late wilt pathogen in infested soils and to evaluate the degree of its prevalence.

How sea urchins face microplastics: Uptake, tissue distribution and immune system response

Plastic pollution represents one of the major threats to the marine environment. A wide range of marine organisms has been shown to ingest microplastics due to their small dimensions (less than 1 mm). This negatively affects some biological processes, such as feeding, energy reserves and reproduction. Very few studies have been performed on the effect of microplastics on sea urchin development and virtually none on adults. The aim of this work was to evaluate the uptake and distribution of fluorescent labelled polystyrene microbeads (micro-PS) in the Mediterranean sea urchin Paracentrotus lividus and the potential impact on circulating immune cells. Differential uptake was observed in the digestive and water vascular systems as well as in the gonads based on microbeads size (10 and 45 μm in diameter). Treatment of sea urchins with particles of both sizes induced an increase of the total number of immune cells already after 24 h. No significant differences were observed among immune cell types. However, the ratio between red and white amoebocytes, indicative of sea urchin healthy status, increased with both particles. This effect was detectable already at 24 h upon exposure to smaller micro-PS (10 μm). An increase of intracellular levels of reactive oxygen and nitrogen species was observed at 24 h upon both micro-PS exposure, whereas at later time these levels became comparable to those of controls. A significant increase of total antioxidant capacity was observed after treatment with 10 μm micro-PS. Overall data provide the first evidence on polystyrene microbeads uptake and tissue distribution in sea urchins, indicating a stress-related impact on circulating immune cells.

A new ophiocistioid with soft-tissue preservation from the Silurian Herefordshire Lagerstätte, and the evolution of the holothurian body plan.

Reconstructing the evolutionary assembly of animal body plans is challenging when there are large morphological gaps between extant sister taxa, as in the case of echinozoans (echinoids and holothurians). However, the inclusion of extinct taxa can help bridge these gaps. Here we describe a new species of echinozoan, Sollasina cthulhu, from the Silurian Herefordshire Lagerstätte, UK. Sollasina cthulhu belongs to the ophiocistioids, an extinct group that shares characters with both echinoids and holothurians. Using physical-optical tomography and computer reconstruction, we visualize the internal anatomy of S. cthulhu in three dimensions, revealing inner soft tissues that we interpret as the ring canal, a key part of the water vascular system that was previously unknown in fossil echinozoans. Phylogenetic analyses strongly suggest that Sollasina and other ophiocistioids represent a paraphyletic group of stem holothurians, as previously hypothesized. This allows us to reconstruct the stepwise reduction of the skeleton during the assembly of the holothurian body plan, which may have been controlled by changes in the expression of biomineralization genes.

Exceptionally preserved soft parts in fossils from the Lower Ordovician of Morocco clarify stylophoran affinities within basal deuterostomes

The extinct echinoderm clade Stylophora consists of some of the strangest known deuterostomes. Stylophorans are known from complete, fully articulated skeletal remains from the middle Cambrian to the Pennsylvanian, but remain difficult to interpret. Their bizarre morphology, with a single appendage extending from a main body, has spawned vigorous debate over the phylogenetic significance of stylophorans, which were long considered modified but bona fide echinoderms with a feeding appendage. More recent interpretation of this appendage as a posterior “tail-like” structure has literally turned the animal back to front, leading to consideration of stylophorans as ancestral chordates, or as hemichordate-like, early echinoderms. Until now, the data feeding the debate have been restricted to evaluations of skeletal anatomy. Here, we apply novel elemental mapping technologies to describe, for the first time, soft tissue traces in stylophorans in conjunction with skeletal molds. The single stylophoran appendage contains a longitudinal canal with perpendicular, elongate extensions projecting beyond hinged biserial plates. This pattern of soft tissues compares most favorably with the hydrocoel, including a water vascular canal and tube feet found in all typical echinoderms. Presence of both calcite stereom and now, an apparent water vascular system, supports echinoderm and not hemichordate-like affinities.

Starfish routing for sensor networks with mobile sink

Wireless Sensor Networks (WSNs) with mobile sinks were proven to provide extended network lifetime and better data delivery services. This was achieved by minimizing routing costs and avoiding development of any hot-spot zones in the network. However, existing routing strategies in the literature have limitations to offer end-to-end data delivery delay and throughput required by the real-time sensing and monitoring applications. In this paper, following the principle of water vascular system of a Starfish, we have designed a routing backbone consisting of a central ring-canal and a number of radial-canals across the network. The radius of the ring-canal and the number of radial-canals are dynamically determined based on the transmission range of sensor nodes and size of the network. The proposed Starfish routing backbone guarantees that each source sensor node gets single-hop access to a backbone node, which in turn facilitates to reduce data delivery delay and increases fairness of energy consumption load distribution on network nodes. The results of the simulation experiments, carried out in NS-2, prove the efficiency of the proposed Starfish routing backbone in terms of end-to-end data delivery delay, throughput and energy consumption compared to state-of-the-art works.

Histological characterization of skin and radial bodies of two species of genus Isostichopus (Echinodermata: Holothuroidea)

Surface morphological structure of the body, and radial organs in sea cucumbers Isostichopus sp. aff badionotus, Isostichopus badionotus morphotype I and I. badionotus morphotype II were characterized by histological techniques. The three morphotypes studied demonstrated differences between them in gross morphology and in the distribution of body fleshy projections in the dorsal region. The body wall consists of a layer of epidermal cells covered by a thin cuticle, a superficial dermis formed by a compact layer of cells with large cytoplasmic contents, slack dermis or delimited connective tissue into the body by a layer of muscle of circular lined by mesothelial cells. Radial bodies are made up of a nerve cord, two channels systems, a channel of water vascular system and five pairs of longitudinal muscles in the ambulacral region. Integument tissue structure showed no differences in the ventral or dorsal region. However, vascular channels through the integument give rise in the dorsal region to different fleshy protrusions wart-like, or fleshy papillae distinctive of each species while in the ventral region ends in podiums. Caribbean sea Isostichopus genus shows good quality skin structure and are able to be commercialized as sandfish or Bêche de mer in international markets.

Regeneration of coelomocytes after evisceration in the sea cucumber, Apostichopus japonicus

Sea cucumber, Apostichopus japonicus, is one of the most important holothurian species cultured in China. Severe evisceration induced by various natural and artificial factors commonly occurs during transport and culture of A. japonicus. Evisceration causes higher mortality and lower yield. Along with the visceral regeneration process, sea cucumbers also regenerate coelomocytes in order to recover immune function. In this study, evisceration of A. japonicus was induced by intracoelomic injection of 0.35 M KCl. Regeneration of coelomocytes was investigated by time course cell counting as well as detection of DNA replication by the EdU labeling technique. Coelomic fluid volume was restored to the pre-evisceration level within 2 h after evisceration. Total coelomocyte count (TCC) reached a peak at 6 h post-evisceration, followed decreased and then increased with a slight fluctuation, restored to the pre-evisceration level at 35 d post-evisceration. The change in different subtypes of coelomocytes was consistent with that of total coelomocytes. However, there were some variations in the regeneration of coelomocyte subtypes. At the end of the study, only the counts of amoebocytes and morula cells recovered to the pre-evisceration level. DNA replication assay showed EdU-positive cells accounted for 9.5% before evisceration and 4.7% at 6 h post-evisceration. However, the percentage of EdU-positive cells significantly increased, reaching 18.6% at 3 d after evisceration, then declined. Therefore, we analyzed the observed increase in coelomocytes at 6 h post-evisceration, which may be due to coelomocyte migration from the water-vascular system into the coelom rather than de novo cell proliferation.

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.

An edrioasteroid from the Silurian Herefordshire Lagerstätte of England reveals the nature of the water vascular system in an extinct echinoderm.

Echinoderms are unique in having a water vascular system with tube feet, which perform a variety of functions in living forms. Here, we report the first example of preserved tube feet in an extinct group of echinoderms. The material, from the Silurian Herefordshire Lagerstätte, UK, is assigned to a new genus and species of rhenopyrgid edrioasteroid, Heropyrgus disterminus The tube feet attach to the inner surface of compound interradial plates and form two sets, an upper and a lower, an arrangement never reported previously in an extant or extinct echinoderm. Cover plates are absent and floor plates are separated creating a large permanent entrance to the interior of the oral area. The tube feet may have captured food particles that entered the oral area and/or enhanced respiration. The pentameral symmetry of the oral surface transitions to eight columns in which the plates are vertically offset resulting in a spiral appearance. This change in symmetry may reflect flexibility in the evolutionary development of the axial and extraxial zones in early echinoderm evolution.

Characterisation of artisanal mine waste on Buru Island, Indonesia and toxicity to the brittle star Amphipholis squamata

Artisanal small-scale gold mining (ASGM) using mercury (Hg) amalgamation commenced on Buru Island, Indonesia, in 2012, but was halted in 2015 due to concerns of widespread Hg contamination. Much of the Hg used in the mining process is lost to trommel waste which is disposed of in settlement ponds that drain into adjacent waterways and into Kayeli Bay. Several thousand unmanaged trommel sites and associated tailing ponds exist on Buru Island. This study shows that waste from the Marloso trommel at the Gogrea site contained 203 mg/kg total Hg (THg), with a negligible proportion present as bioavailable methyl Hg (MeHg) and a low total organic carbon content. There are currently very few tools available for ecotoxicological risk assessment of mine tailings for tropical marine ecosystems, and we support the development of Tailings Toxicity Tests (TTTs) and describe laboratory toxicity test methods using the cosmopolitan benthic echinoderm Amphipholis squamata. Undiluted trommel waste caused 100% mortality of A. squamata within 48 h, and a 96-h LC50 of 6.7% w/w trommel waste (4 mg/kg THg) was estimated. Sub-lethal effects on the water vascular system of the brittle star were assessed by quantification of the Ability to Right Itself (ARI), and a 48-h EC50 of 7.3% w/w trommel waste (14.4 mg/kg THg) was estimated. The results show that trommel waste produced on Buru Island is highly contaminated with THg and is acutely toxic, raising serious concern for receiving ecosystems where Hg methylation to more toxic and bioavailable forms is likely.

Effects of CO2, pH and temperature on respiration and regeneration in the burrowing brittle stars Hemipholis cordifera and Microphiopholis gracillima

Hemipholis cordifera and Microphiopholis gracillima are burrowing brittlestars that differ in burrow architecture and oxygen obtaining strategies: M. gracillima actively ventilates a gallery while H. cordifera has a simple chamber and instead relies on oxygen being transported from arms exposed to the overlying water using hemoglobin in its water vascular system. To determine the possible effects of near future climate change on both species, in terms of metabolism and regeneration, they were exposed to current (25°C & 28°C) and elevated (32°C) temperatures, as well as normal (8.1) and hypercapnia/lowered pH (7.8 & 7.6) in all combinations for six weeks. Oxygen uptake was measured weekly during this period. As expected, M. gracillima had a higher overall oxygen uptake rate than H. cordifera. Both species had highly variable oxygen uptake and were significantly affected by the week was measured. H. cordifera experienced increased oxygen uptake at the higher temperature (32°C) and as a result of interactive effects of time and pH7.6. Both species experienced interactive effects of pH and temperature, but there was no clear pattern. Increased temperature positively affected arm regeneration in H. cordifera, increasing both length and percent recovery. There were no effects on disc regeneration observed in M gracillima, however lower pH decreased the dry weight in both intact and regenerating animals. Calcification, measured as percent inorganic content, was not affected in either species by regeneration, temperature or pH. Despite the minor effects on its physiology, M. gracillima experienced lower percent survivorship than H. cordifera. Temperature had the most effect, with survivorship higher at 28°C, than at 25°C or 32°C. These results indicate that both species are operating near or at their physiological limits and may be unable to cope with future drastic changes.