Water Vascular System Research Articles

Testing for homologies in the axial skeleton of primitive echinoderms

AbstractThe extraxial axial theory is used to investigate homology of ambulacral and oral plating because it predicts terminal branching and terminal addition of plates in the axial skeleton, although exceptions to the former may occur in some Paleozoic echinoderms. The variety of morphological designs and anomalous individuals also provide tests of plate homology. Homology of ambulacra is generally accepted, with the hydropore and/or single gonopore in Carpenter’s CD interray. In the 2-1-2 ambulacral pattern the unbranched ambulacrum is always in Carpenter’s A ray. All ambulacral morphology requires just three instructions: ‘grow,’ ‘branch,’ and ‘stop.’ The range of variation in echinoderms with fewer than five ambulacra implies that both the ‘branch’ and ‘stop’ instructions acted independently in all five rays. Numbers of ambulacra may or may not correlate with numbers of orals. Two basic patterns of ‘cystoid’ oral plating occur; with a single radial (circum-oral, CO) plate from each ambulacrum plus a sixth in the CD interray, and with all six interradial peri-oral (PO) plates, with two in the CD interambulacrum. Five ‘orals’ may involve loss of PO3 or PO6. Erect ambulacral structures are lost first in taphonomy and so poorly known. All ambulacral skeletal elements bear the same topological relationship to ambulacral soft tissues. Where branched ambulacra occur, the trunk or flooring plates are often modified first brachiolars or pinnulars. Both brachioles and pinnules may arise from facets developed on one or two flooring plates. Terminal addition of plates, spacing of brachioles/pinnules, and lack of musculature to open cover plates all suggest that ‘cystoids’ had extensions of the water vascular system in their ambulacra.

Microscopic anatomy of the axial complex and associated structures in the sea cucumber Chiridota laevis Fabricius, 1780 (Echinodermata, Holothuroidea)

The absence of axial and pericardial coeloms and the axial organ, presence of a mesocoelomic tentacular apparatus, correspondence of the larval sagittal plane with the madreporic plane of the adult, and some other peculiarities set holothurians apart from all other echinoderms. We studied the holothuroid Chiridota laevis with histological methods and constructed a 3D-model. The bilateral symmetry of the water-vascular system is clear in spite of a peculiar coelomic connection with one of the tentacles in radius D. The somatocoelomic and axocoelomic perihaemal coeloms are absent. There are perioral and water-vascular circumoral coelomic rings. The hyponeural ring is absent. Each radial complex includes a water-vascular canal, a hyponeural canal, two nerve bands (ectoneural and hyponeural), and the non-coelomic epineural canal. The stone canal starts from the water ring on the aboral side in the CD interradius and ends with a madreporic ampulla, from which a few pores open into the perivisceral coelom, and one pore canal opens into the environment. This organization seems to be the intermediate state between most echinoderms, in which the madreporic pores open into the environment, and the typical organization of holothurians, in which the madreporic pores open into the perivisceral coelom. The histological structure of the oral haemal ring resembles the axial organ of other Eleutherozoa. The haemocoel lacune of the stone canal communicates with the haemal system of the gonad, the oral haemal ring, and the gut haemocoel lacunae. The genital coelom is represented by narrow spaces surrounding the “genital rachis” of the gonad.

Population pharmacokinetics of enrofloxacin in purple sea stars (Pisaster ochraceus) following an intracoelomic injection or extended immersion.

OBJECTIVE To determine population pharmacokinetics of enrofloxacin in purple sea stars (Pisaster ochraceus) administered an intracoelomic injection of enrofloxacin (5 mg/kg) or immersed in an enrofloxacin solution (5 mg/L) for 6 hours. ANIMALS 28 sea stars of undetermined age and sex. PROCEDURES The study had 2 phases. Twelve sea stars received an intracoelomic injection of enrofloxacin (5 mg/kg) or were immersed in an enrofloxacin solution (5 mg/L) for 6 hours during the injection and immersion phases, respectively. Two untreated sea stars were housed with the treated animals following enrofloxacin administration during both phases. Water vascular system fluid samples were collected from 4 sea stars and all controls at predetermined times during and after enrofloxacin administration. The enrofloxacin concentration in those samples was determined by high-performance liquid chromatography. For each phase, noncompartmental analysis of naïve averaged pooled samples was used to obtain initial parameter estimates; then, population pharmacokinetic analysis was performed that accounted for the sparse sampling technique used. RESULTS Injection phase data were best fit with a 2-compartment model; elimination half-life, peak concentration, area under the curve, and volume of distribution were 42.8 hours, 18.9 μg/mL, 353.8 μg•h/mL, and 0.25 L/kg, respectively. Immersion phase data were best fit with a 1-compartment model; elimination half-life, peak concentration, and area under the curve were 56 hours, 36.3 μg•h/mL, and 0.39 μg/mL, respectively. CONCLUSIONS AND CLINICAL RELEVANCE Results suggested that the described enrofloxacin administration resulted in water vascular system fluid drug concentrations expected to exceed the minimum inhibitory concentration for many bacterial pathogens.

Anterior regeneration after fission in the holothurian Cladolabes schmeltzii (Dendrochirotida: Holothuroidea).

The regeneration of the anterior portion of the body after fission was studied in the holothurian Cladolabes schmeltzii using electron microscopy methods. Following fission, the posterior portion of the digestive tube, cloaca, and respiratory trees remain in the posterior fragment of the body. The regeneration comprises five stages. In the first stage, connective-tissue thickening (an anlage of the aquapharyngeal bulb) occurs on the anterior end between the torn-off ends of the ambulacra. Most of the lost anterior organs developed in the second and third stages. The structures of water-vascular system and nerve ring form through dedifferentiation, proliferation, and migration of cells of the radial water-vascular canals and the radial nerve cords, correspondently. The lost digestive system portion is restored through the formation and merging of two anlagen. The digestive epithelium of the esophagus and pharynx develops from lining cells of microcavities near the central portion of the connective-tissue thickening, which probably migrate from the epidermis. The second gut anlage develops through transformation of the anterior gut remnant portion. The enterocytes partly dedifferentiate, but the epithelium retains integrity. The gut anlage grows down the mesentery and joins the regenerating aquapharyngeal bulb. In the fourth and fifth stages, all lost organs are formed and have nearly normal structure. The regeneration was concluded to occur through morphallactic rearrangements of the remaining parts of organs. Epithelial morphogenesis is the key development mechanism of the digestive, water-vascular, and nervous systems.

Low coverage sequencing of three echinoderm genomes: the brittle star Ophionereis fasciata, the sea star Patiriella regularis, and the sea cucumber Australostichopus mollis

BackgroundThere are five major extant groups of Echinodermata: Crinoidea (feather stars and sea lillies), Ophiuroidea (brittle stars and basket stars), Asteroidea (sea stars), Echinoidea (sea urchins, sea biscuits, and sand dollars), and Holothuroidea (sea cucumbers). These animals are known for their pentaradial symmetry as adults, unique water vascular system, mutable collagenous tissues, and endoskeletons of high magnesium calcite. To our knowledge, the only echinoderm species with a genome sequence available to date is Strongylocentrotus pupuratus (Echinoidea). The availability of additional echinoderm genome sequences is crucial for understanding the biology of these animals.FindingsHere we present assembled draft genomes of the brittle star Ophionereis fasciata, the sea star Patiriella regularis, and the sea cucumber Australostichopus mollis from Illumina sequence data with coverages of 12.5x, 22.5x, and 21.4x, respectively.ConclusionsThese data provide a resource for mining gene superfamilies, identifying non-coding RNAs, confirming gene losses, and designing experimental constructs. They will be important comparative resources for future genomic studies in echinoderms.Electronic supplementary materialThe online version of this article (doi:10.1186/s13742-016-0125-6) contains supplementary material, which is available to authorized users.

Biological characterization of the reproductive cycle of the sea urchin (Paracentrotus lividus) in the western central region of Portugal (Peniche)

Biological characterization of the reproductive cycle of the sea urchin (Paracentrotus lividus) in the western central region of Portugal (Peniche)

Lesions of Copper Toxicosis in Captive Marine Invertebrates With Comparisons to Normal Histology

Despite increasing concern for coral reef ecosystem health within the last decade, there is scant literature concerning the histopathology of diseases affecting the major constituents of coral reef ecosystems, particularly marine invertebrates. This study describes histologic findings in 6 species of marine invertebrates (California sea hare [Aplysia californica], purple sea urchin [Strongylocentrotus purpuratus], sunburst anemone [Anthopleura sola], knobby star [Pisaster giganteus], bat star [Asterina miniata], and brittle star [Ophiopteris papillosa]) with spontaneous copper toxicosis, 4 purple sea urchins with experimentally induced copper toxicosis, and 1 unexposed control of each species listed. The primary lesions in the California sea hare with copper toxicosis were branchial and nephridial necrosis. Affected echinoderms shared several histologic lesions, including epidermal necrosis and ulceration and increased numbers of coelomocytes within the water-vascular system. The sunburst anemone with copper toxicosis had necrosis of both epidermis and gastrodermis, as well as expulsion of zooxanthellae from the gastrodermis. In addition to the lesions attributed to copper toxicosis, our results describe normal microscopic features of these animals that may be useful for histopathologic assessment of marine invertebrates.

The effect of copper and temperature on juveniles of the eurybathic brittle star Amphipholis squamata – Exploring responses related to motility and the water vascular system

The limited availability of test organisms that represent tropical and deeper water environments is a significant concern when assessing the risk of contaminants in these environments. Amphipholis squamata (Delle Chiaje 1828) is a widely distributed brittle star with many phylogenetic clades reported from different latitudes, and it also occurs from the intertidal zone to a depth of ∼1300m. In the present study, the effect of copper on four behavioural responses and mortality of A. squamata were quantified at four different temperatures including 25, 20, 15 and 10°C. At 25°C the four behavioural responses and mortality were relatively sensitive to copper, with 96h EC50 values of 25 (confidence interval 18–44), 24 (7–26), 32 (24–41), 29 (9–41)μgL−1 for the measured ability to turn from the oral surface up to oral surface down, curling behaviour, tube foot movement, and tube foot retraction respectively. The average 96-h LC50 value for copper at 25°C was 46μgL−1. Some endpoints investigated showed significant effects of reduced temperature compared to the optimal temperature. These effects were enhanced with increasing copper concentrations and significant differences in copper toxicity between temperature treatments were most notable when measuring the ability to turn from the oral surface up to oral surface down where the EC50 changed from 25 (18 to 44) to 6 (−18 to 14) μgL−1 with a reduction of temperature from 25 to 15°C. The results showed that A. squamata is relatively sensitive to copper and that further investigation into the effects of other stressors on these endpoints is warranted.

Sea urchin Diadema africanum mass mortality in the subtropical eastern Atlantic: role of waterborne bacteria in a warming ocean

A widespread mass mortality event of the sea urchin Diadema africanum was detected in the subtropical eastern Atlantic, extending from Madeira to the Canary Islands, covering a straight- line distance of >400 km. This is the first disease- related die-off of a diadematid documented in the eastern Atlantic Ocean. Diseased individuals showed deterioration of the epidermis and water-vascular system, resulting in epidermal necrosis and release of spines. Despite some spatial heterogeneity in disease incidence at the study sites, there was a 65% overall reduction in urchin abundance after the mortality event compared to numbers pre-mortality. However, the reduction in urchin numbers did not compromise the species' reproductive success; the settlement peak following the mortality event was of a similar magnitude to that in prior years. Bacterial isolation and cul ture techniques, and subsequent laboratory in fection experiments, strongly suggested that Vibrio alginolyticus was involved in the disease. We hypo thesize that the mass mortality event devel- oped due to anomalously high seawater tempera- tures recorded in the 2 studied archipelagos and that warmer temperatures enabled infection of D. africa - num by waterborne pathogenic bacteria. Fluctua- tions in urchin populations are key in de termining the structure and functioning of benthic ecosystems: under the current seawater warming scenario, dis- ease may result in more frequent phase shifts, aiding the persistence of macroalgae.

Development of the sea urchins Temnopleurus toreumaticus Leske, 1778 and Temnopleurus reevesii Gray, 1855 (Camarodonta: Temnopleuridae)

Sea urchin larvae near metamorphosis form an adult rudiment that is a complex of the juvenile structures. However, the details of the mechanisms that form the adult rudiment are unknown. The temnopleurid sea urchins Temnopleurus toreumaticus and Temnopleurus reevesii occur in Japan, but the development of their juvenile morphology has not been described. In this study, we observed their development by light and scanning electron microscopy to follow the adult rudiment formation and to consider the mechanisms of evolution of juvenile morphology in sea urchins. The prism embryos of both species formed two primary pore canals that elongated from the left and right coelomic sacs; the left canal connected the presumptive water vascular system to the hydropore. These organs were formed bilaterally and symmetrically in T. toreumaticus and with left-right asymmetry in T. reevesii. The right canal of both species had degenerated by the four-armed larval stage. At the prism stage, about six cells from the left oral ectoderm located between the left post-oral arm and the oral lobe formed a cell mass. The cell mass grew in diameter stepwise in T. toreumaticus by cell migration and by the formation of an epithelial pouch during the four- to six-armed larval stages and more rapidly in T. reevesii by the formation of a thin epithelium during the six-armed larval stage. In both species, the adult rudiment was formed by attachment of the cell mass to the hydrocoel. The larvae of T. toreumaticus metamorphosed from a tiny hole on the left ectoderm between the post-oral and postero-dorsal arms. These findings suggest that the developmental process involving the formation of two primary pore canals and a cell mass may have been acquired and conserved as common traits in the early development of indirect-developing temnopleurid species during evolutionary divergence from the Cidaroida.

Comparison of cells free in coelomic and water-vascular system of sea cucumber, Apostichopus japonicus

The sea cucumber, Apostichopus japonicus possesses a variety of cells populating in both the coelomic (cells in the coelomic are called coelomocytes) and water-vascular system. In this study, we compared cells in these two systems of A. japonicus on total cell number, cell types and surface antigens through monoclonal antibodies against coelomocytes. The results demonstrated that the cell types observed in coelomic also could be found in water-vascular system, but the total cell number and percentages of each type were different. The total number of coelomocytes was 2–3 times of that in water-vascular system. Lymphoid cells were numerically dominant in coelomic system, while spherulocytes with pseudopods in water-vascular system. Results of indirect immunofluorescence assay technique showed that both coelomocytes and cells in water-vascular system could be recognized by the corresponding MAbs, and the distribution of its positive signals was not different. In conclusion, cell types and surface antigens in coelomic and water-vascular system were same, but the total cell number and percentages of each type were different. And further researches are needed on whether there are differences in functions of the different composition.

Morphologic and systematic revision of the solute Maennilia estonica (Homoiostelea, Echinodermata) from the Upper Ordovician of Estonia

Maennilia estonica Rozhnov and Jefferies was first described as a stem-chordate but restudy shows it is an unusually large homoiostelean echinoderm. Its feeding structure, an erect ambulacrum, extending exothecally from the peristomial frame plates, bears a large internal tunnel that opens directly into the body cavity. This type of feeding appendage is now recognized to be unique to homoiosteles. It bears no evidence for water vascular system impressions adjacent to its food groove. The theca has poorly developed marginal plates and a narrow rim that, in contrast to some other homoiosteles, does not extend over either lower or upper thecal face. Maennilia appears to have inhabited the deeper portions of a near-shore environment in limey muds adjacent to a linear zone of bryozoan and microbial bioherms.

Re‐evaluating the palaeobiology and affinities of the Ctenocystoidea (Echinodermata)

Synopsis Ctenocystoids are a poorly understood group of fossil deuterostomes, with little known about their morphology, palaeobiology or affinities. A three‐dimensional specimen of the ctenocystoid Ctenocystis utahensis from the Middle Cambrian Spence Shale (western USA) was imaged using X‐ray microtomography and digitally reconstructed. This allowed the species to be described in greater detail than previously possible, providing a number of morphofunctional insights. Two openings are identified: (i) an anterior opening controlled by moveable plates in the distinctive ctenoid apparatus and (ii) a wide posterior periproct. A putative third body opening (hydropore and/or gonopore) is not present, contrary to previous reconstructions. Ctenocystis utahensis was most probably epibenthic, facing into water currents during life. Suspended food particles entered paired lateral grooves within the ctenoid apparatus through gaps between neighbouring ctenoid plates; when the ctenoid apparatus was open, material could pass from these lateral grooves to an internal chamber, which led into the main body cavity. Our reconstruction demonstrates that the plates of the ctenoid apparatus and the lateral feeding grooves are not homologous with paired brachioles, refuting suggestions that ctenocystoids are derived blastozoans. Instead, it is probable that ctenocystoids are basal stem‐group echinoderms, sharing several plesiomorphies (a bilateral body plan, pharyngeal gill slits and a paired water vascular system) with the latest common ancestor of echinoderms plus hemichordates. Reconstructing the anatomy of ctenocystoids in three‐dimensions is critical to a full understanding of their palaeobiology and phylogenetic position.

The oldest cinctan carpoid (stem-group Echinodermata), and the evolution of the water vascular system

A new cinctan (Protocinctus mansillaensis gen. et sp. nov.), from the early Middle Cambrian of the Iberian Chains (north-east Spain), is described with the aid of X-ray microtomography and three-dimensional computer models. Investigation in this manner was possible because of the unusual condition of the fossils, which are preserved as recrystallized calcite. Protocinctus gen nov. possesses an elongate body with a single left anterior feeding groove and an open posterior marginal frame (in ventral view): this combination of characters is unique amongst cinctans. Through the study of original specimens and ‘virtual fossils’ it was possible to reconstruct the palaeobiology of Protocinctus gen. nov.: cinctans are interpreted as pharyngeal basket feeders with a U-shaped gut, using their posterior appendage to aid stability on the sediment surface. Cinctans are critical to understanding the evolutionary history of the echinoderm stem group, as they illustrate the transition from a paired water vascular system (basal) to one constructed from just the left hydrocoel (derived). The former condition is also observed in another group of stem-group echinoderms, the ctenocystoids, and is hypothesized for the latest common ancestor of the echinoderms and hemichordates.

Phylum Echinodermata*

The Phylum Echinodermata, comprising approximately 7,000 living species, and 13,000 fossil species, is epitomized by the familiar sea star, a universal symbol of the marine realm. This distinctive group of animals may be briefly defined as possessing a skeleton of calcium carbonate in the form of calcite; a unique water-vascular system which mediates feeding, locomotion, and other functions; and a more or less conspicuous five-part radial symmetry. A closer look at some extant echinoderms will show that some taxa of sea cucumbers lack calcite in their body walls, some taxa of sea stars have “outgrown” five-part symmetry and may have 50 or more arms, and many echinoderms show a more or less conspicuous bilateral symmetry superimposed upon a radial pattern. Fossil echinoderms can be even more puzzling, for some are decidedly asymmetrical, and others may lack evidence of a water-vascular system. Perhaps the only truly reliable taxonomic character of the phylum is that its members today are restricted to the marine realm.

Echinoderms

Echinoderms

The pre‐radial history of echinoderms

AbstractGene sequence data now identify a robust phylogeny of deuterostomes and provide a framework within which the evolution of echinoderms can be interpreted. The topology of the molecular tree makes a number of important predictions about the morphological characters of the earliest echinoderm at its split from hemichordates: it possessed gill slits (but not a notochord), had a bilaterally symmetrical body plan in the adult and, less certainly, underwent torsion during development. Carpoids, a highly contentious group of extinct deuterostomes with a plated calcite skeleton that have variously been interpreted as stem‐ and crown‐group chordates, stem‐group echinoderms or stem‐ and crown‐group echinoderms, display many of these basal characters and provide critical evidence for how the latest common ancestor of hemichordates and echinoderms was transformed into a pentaradiate crown‐group echinoderm.Cinctans have a large atrial opening in addition to mouth and anus, and are interpreted as pharyngeal basket feeders. The paired grooves associated with the mouth indicate the presence of a hydrovascular system, but not necessarily one built along the echinoderm plan (that is, derived from just the left hydrocoel). Stylophorans have a bilateral body plan that is externally masked by torsion and possess gills, either unpaired and external, or paired and internal, opening into an atrial cavity. Their bilateral appendage is a locomotory organ, not an ambulacrum, and there is no evidence that stylophorans ever possessed a well‐developed hydrovascular system homologous to the water vascular system of echinoderms and the tentacles of pterobranch hemichordates. Solutes are the most crownward, having a true echinodermal ambulacral system with a single hydropore and no pharyngeal gill openings. Copyright © 2005 John Wiley & Sons, Ltd.

Comparative histological and immunohistochemical study of sea star tube feet (Echinodermata, Asteroidea)

Adhesion in sea stars is the function of specialized structures, the tube feet or podia, which are the external appendages of the water-vascular system. Adhesive secretions allow asteroid tube feet to perform multiple functions. Indeed, according to the sea star species considered, the tube feet may be involved in locomotion, fixation, or burrowing. Different tube foot shapes usually correspond to this variety of function. In this study, we investigated the variability of the morphology of sea star tube feet as well as the variability of the composition of their adhesive secretions. This second aspect was addressed by a comparative immunohistochemical study using antibodies raised against the adhesive material of the forcipulatid Asterias rubens. The tube feet from 14 sea star species representing five orders and 10 families of the Class Asteroidea were examined. The histological study revealed three main tube foot morphotypes, i.e., knob-ending, simple disc-ending, and reinforced disc-ending. Analysis of the results suggests that tube foot morphology is influenced by species habitat, but within limits imposed by the evolutionary lineage. In immunohistochemistry, on the other hand, the results were very homogeneous. In every species investigated there was a very strong immunolabeling of the adhesive cells, independently of the taxon considered, of the tube foot morphotype or function, or of the species habitat. This indicates that the adhesives in all the species considered are closely related, probably sharing many identical molecules or, at least, many identical epitopes on their constituents.

The aboral surface of Asterias rubens L. (Echinodermata: Asteroidea) during metamorphosis with particular reference to the hydropore and madreporite

Summary The aboral development of the asteroid Asterias rubens L. is described for the first time using scanning electron microscopy (SEM). The study extends from the advanced brachiolaria stage of the larva until the postmetamorphic stage of the juvenile. Special emphasis is given to the fate of the hydropore and the appearance of the madreporite, which have never been documented with SEM before. Contrary to expectation, SEM has shown that the hydropore is resorbed during the final stage of metamorphosis, and the madreporite arises as a strongly ciliated, sinuous groove, near the closed hydropore. Consequently, the hydropore cannot be the primary madreporite pore, and A. rubens may go through a transitional period without a functional metanephridial system where it also lacks other vital functions. Additionally, it is shown that initially the juvenile has no madreporite, papulae and pedicellariae. These structures first appear on the surface after metamorphosis has been completed. The function of the aboral test appendages, the pore canal-hydropore complex (larval metanephridial system) and the axial complex (adult metanephridial system) are discussed. The axial complex succeeds the pore canal-hydropore complex during the radical metamorphosis which includes (1) resorption and dedifferentiation of larval structures, and (2) differentiation and growth of adult structures. The former complex may be functional by the time the pore openings appear at the bottom of the grooves of the madreporite at the postmetamorphic stage. Seen from the traditional view, the presence of the madreporite also indicates that the juvenile has a functional water vascular system in every respect.

Toxic effects of endocrine disrupters on freshwater sponges: common developmental abnormalities

Endocrine disrupters are of substantial concern, in large part because effects of these compounds on the growth and development of many aquatic organisms are unknown. We examined toxic effects of three substances (ethylbenzene, nonylphenol, and bisphenol A), that are known to be hormonally active in many animals, on growth and development of two species of freshwater sponge. A common developmental abnormality was observed when sponges were treated with each of these compounds. The three compounds also caused significant reductions in growth rates. Lower concentrations resulted in malformed water vascular systems in several replicates. The utility of freshwater sponge bioassays is discussed as it relates to understanding possible mechanisms of action of endocrine disrupters on aquatic invertebrates.