Progesterone metabolism by the echinoderms Asterias rubens and Marthasterias glacialis (Short Communication)

The echinoderms Asterias rubens and Marthasterias glacialis metabolize injected [4-(14)C]progesterone to give labelled 3beta-hydroxy-5alpha-pregnan-20-one and 3beta,6alpha-dihydroxy-5alpha-pregnan-20-one. These radioactive products are converted by the animals into conjugated forms that are soluble in aqueous methanol, and which have mobilities on t.l.c. similar to the asterosaponins.     

La structure fine des caecums rectaux de deux Asteriidae: Marthasterias glacialis (L) et Coscinasterias tenuispina (Lam) (Echinodermata,Asteroidea)

Résumé Dans les caecums rectaux des deux espèces étudiées, stratification tissulaire et composition cellulaire sont semblables. L'épithélium interne se compose de mucocytes et de cellules banales. Outre du glycogène, ces dernières renferment chez M. glacialis des grains de mucopolysaccharides neutres associés à des protéines tandis que chez C. tenuispina, les granules contiennent des mucopolysaccharides acides carboxylés et sulfatés également associés à des protéines. L'épithélium externe de C. tenuispina présente, outre des cellules banales, des cellules glandulaires à contenu protéique.Une attention particulière a été apportée à l'ultrastructure du pôle apical des cellules banales internes. On y remarque de nombreuses microvillosités et un flagelle central caractéristique. De plus, on observe très fréquemment des formations pinocytaires ainsi que plus rarement de la phagocytose. Les diverticules seraient donc, chez les Asteriidae, des organes digestifs à part entière se caractérisant par un grand pouvoir d'absorption et une digestion intracellulaire.Enfin, le pôle basal des cellules banales internes, très contourné, contient, par endroit, des -cytomembranes typiques. Il est possible qu'à ce niveau aient lieu des transferts de substances vers le coelome.

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The fine structure of the rectal caeca of two asteriidae: Marthasterias glacialis (L) and Coscinasterias tenuispina (Lam) (echinodermata asteroidea)

Summary Histological and cytological composition are similar in the rectal caeca of both studied species. Internal epithelium is composed of mucocytes and of banal cells. Besides glycogen, these cells contain in M. glacialis neutral mucopolysaccharides associated with proteins, while in C. tenuispina, the granules contain acidic carboxyled and sulfated mucopolysaccharides also associated with proteins. The external epithelium of C. tenuispina presents, besides banal cells, granular secretory cells with proteic content.Special attention has been payed to the ultrastructure of the apical pole of the internal banal cells. One notices numerous microvilli and a characteristic central flagellum. Moreover, one frequently observes pinocytic formations as well as—more rarely—phagocytosis. The rectal diverticula would thus be, in the Asteriidae, real digestive organs provided with a great capacity of absorption and intracellular digestion.The basal pole of the internal banal cells contains from place to place typical -cytomembranes. Transfers of substances to the coelom can occur at that level.

Madame Klinkert, Mademoiselle Bricourt et Monsieur Harray ont collaboré à la réalisation technique de ce travail. Nous les en remercions grandement. — Le séjour à la station zoologique de Naples a eu lieu grâce à l'appui financier du Ministère de l'Education Nationale et de la Culture.     

Acrosomal reaction and early events at fertilization in Marthasterias glacialis (Echinodermata: Asteroidea)

When the spermatozoon of M glacialis contacts the mature oocyte jelly it adheres to it. Following this, there is a slight tumefaction of the acrosome, which is followed by the disruption of the apical acrosomal vesicle and cytoplasmic membranes. Acrosomal vesicle contents are liberated and spread along the outer surface of the oocyte jelly. Meanwhile, the acrosomal process begins to extend, penetrates all the jelly extension, then the vitelline layer, and finally contacts the cytoplasmic egg membrane. Nevertheless, the sperm cell continues lying at the outer border of the jelly. From the beginning of the acrosome reaction the dense and finely fibrillar subacrosomal material is connected, by some expansions, to the basal acrosomal vesicle membrane. Both nuclear and mitochondrial diameters have diminished.     

Fine structural study of the acrosome formation in the starfish Marthasterias glacialis (Echinodermata, Asteroidea)

The fine structure of the spermatogenic cells in the starfish Marthasterias glacialis was studied regarding acrosome formation. The main finding in the spermatogenesis of M. glacialis is that the formation of the pro-acrosomal vesicles seems to be initiated in late spermatogonia. Small dense bodies resulting from the division of large granulofibrillar masses were also observed in the cytoplasm of late spermatogonia. During spermiogenesis the inner acrosomal vesicle membrane becomes coated first with dense materials originated from the cytoplasmic dense bodies and then with cisternae of endoplasmic reticulum. Both coating materials are incorporated in the periacrosomal space of the mature acrosome. Besides being involved in the genesis of the periacrosomal material, cytoplasmic dense bodies were also seen in close relationship with intercellular bridges and midpiece structures of spermatids. These findings are discussed in comparison with other echinoderm spermatogenesis.     

Phylogeny and classification of the Asteroidea (Echinodermata)

Post-Palaeozoic asteroids share a large number of derived characters of the ambulacral column and the mouth frame, and constitute the crown group of the monophyletic group Asteroidea. This crown group is here called the Neoasteroidea (new subclass). The stem species of the crown group lived in the Permian or early Triassic and so the evolution of the asteroids parallels that of the echinoids. Character distribution within the Neoasteroidea, especially morphology of the skeleton, digestive system, larvae and tube feet, allows subdivision into four orders (Paxillosida, Notomyotida, Valvatida, Forcipulatida). The latter three orders possess the synapomorphy of suckered tube feet and are united as the Surculifera (new superorder); the Paxillosida are their primitive sister group. Palaeozoic asteroids represent the stem group of the class, and may be divided into plesions according to the order of appearance of synapomorphies with the crown group. Classification of Palaeozoic asteroids requires much further study. The appearance of new characters within the crown group asteroids, such as suckered tube feet, implies that these were absent in the stem group. The range of life-habits possible in Palaeozoic asteroids can thus be partly deduced from evidence provided by living asteroids. Palaeozoic asteroids are deduced to have lacked suckered tube feet and were presumably unable to evert the stomach; hence they were precluded from life on hard substrates and extraoral feeding on epifaunal organisms. It is suggested that they lived on soft substrates by deposit feeding, scavenging and predation on small benthos.     

Choanocyte-like cells in the digestive system of the starfish Marthasterias glacialis (Echinodermata)

Two types of choanocyte-like cells have been found in the digestive tract of the starfish. Type I choanocytes are in the lining epithelium of all organs of the digestive system. These are narrow, columnar cells strongly anchored basally and expanded apically into a protuberance projecting into the lumen. A prominent flagellum surrounded by microvilli projects from the center of this protuberance. Apical cytoplasm contains numerous mitochondria, secondary lysosomes, and multivesicular bodies. A distinctive characteristic of these cells is a filament bundle that traverses the length of the cell from its region of attachment on the rootlet of the flagellar basal body to its terminus on the basal plasma membrane. Between the attenuated basal ends of type I cells are the nerve fibers of an intraepithelial nerve plexus. Thickness of the plexus is correlated with the quantity of type I cells in the epithelium. Type II choanocytes are in the cuboidal coelomic epithelium that forms the outer layer of digestive tract organs. These cells are smaller than those of type I, and they have an apical collar surmounted by a ring of 13 microvilli. Within the collar is a cup-shaped depression with a central flagellum. Coated vesicles, secondary lysosomes, and phagocytic infoldings are observed in and near the collar cytoplasm. Filament bundles similar to those in type I choanocytes are also observed in coelomic epithelial cells that are sufficiently tall. Injection of peroxidase into the stomach and ferritin into the coelom results in phagocytic uptake of these macromolecules by type I and type II choanocytes, respectively.     

The aboral haemal system of the sea star,Asterias rubens (Echinodermata,Asteroidea): An ultrastructural and histochemical study

Summary The aboral parts of the haemal system of the sea star Asterias rubens are described, based on light and electron microscopy. These parts are (1) the mesenteric strands along the pyloric caeca and the pyloric stomach, (2) the gastric haemal tufts, and (3) the aboral haemal ring. The mesenteric haemal strands are very limited in size and distribution and, therefore, do not seem to have a major function in nutrient translocation. The myoepithelial cells of the gastric haemal tufts have the typical features of choanocytes; their ultrastructural characteristics corroborate the possible absorptive role of the gastric haemal tufts. The myoepithelial cells of the aboral haemal ring often show distinct apical bulbs of cytoplasm suggesting apocrine secretion of PAS-positive materials which are found in the surrounding aboral coelomic ring. These cells contain large stores of particulate glycogen and typical 1–2 m electrondense globules.The ground substance of the haemal tissues, which contains collagen fibers, reticular fibrils, and numerous amoeboid phagocytes, has been analyzed histochemically. Sulfated glycosaminoglycans are almost completely absent; the predominant components are polysaccharides, proteins, and/or glycoproteins. Lipids have not been demonstrated.The possible functions of the haemal tissues and associated coelomic channels are discussed.     

A chemical alarm response in Pycnopodia helianthoides (Echinodermata: Asteroidea)

Adult Pycnopodia helianthoides exhibit a classic alarm response, moving away from fragments and tissue fluid of the tube feet, pyloric caeca, and body wall of conspecific individuals.     

Skeletal growth in the echinoderm Asterias rubens L. (Asteroidea,Echinodermata) estimated by 45Ca-labelling

The skeletal dry weight of the 4.4 ± 0.2 cm size class of Asterias rubens L. from Kiel Bay in the western Baltic is 0.34 ± 0.08 g. The sum of calcium and magnesium carbonates in the skeleton amounts to 94.0 ± 1.3% while the individual concentrations are 86.9 ± 1.3% CaCO₃ and 7.1 ± 0.7% MgCO₃. The MgCO₃ is 4% lower than expected for a magnesium calcite precipitated under Baltic temperature conditions (8°C). Strontium was not determined but strontium carbonate is known to be in the region of 0.4%. The remainder is organic matter and this gives rise to 2.9 ± 1.3% organic carbon.Animals studied were at the ‘waiting stage’ and their actual growth was minimal. Uptake of ⁴⁵Ca in the skeleton consists of a fast step followed by a slow step. The fast step is attributed to saturation of exchangeable skeletal pools while the slow step is due to net deposition of CaCO₃. Skeletal growth at the waiting stage calculated from the second rate constant was found to be 0.76 μg CaCO₃j-mg skeleton^?1 · day^?1 or 0.09% · day^?1 compared with 9.3 μg CaCO₃ · mg skeleton^t1̄ · day^?1 or 1.1% · day^?1 at log phase. The isotope method is considered superior to size-frequency analysis in that it is capable of detecting differences in growth rate in individuals of the same size class and thus provides an insight into asteroid population structure.     

Fine structure of the spermatozoon of Marthasterias glacialis (Linnaeus) (Echinodermata; Asteroidea), with special reference to acrosomal morphology

The sperm of Marthasterias glacialis (Linnaeus) was studied by light and electron microscopy. It is a long uniflagellated cell of the “primitive” type. The head has a spherical shape and contains a nucleus with a spheroid acrosome lying in a cup-shaped anterior fossa. The acrosome is formed by an acrosomal vesicle surrounded by the periacrosomal material. The basal specializations of the acrosomal vesicle show a clear differentiation of its constituents resembling the structure of membrane. The midpiece contains a very large annular mitochondrion which encircles two perpendicular centrioles. The distal centriole is in close association with a pericentriolar radial complex. The tail, containing a common microtubular axoneme, is projected to a variable position.     

Functional morphology of the pedicellariae of the asteroid Marthasterias glacialis (Echinodermata)

Summary Marthasterias glacialis bears two kinds of pedicellariae. The straight pedicellariae are single and occur everywhere on the asteroid body surface except in the ambulacral groove. The crossed pedicellariae are clustered on mobile structures (the rosettes) build around marginal and abactinal spines.Basically, each pedicellaria has a head and a stalk. A skeleton occurs only in the pedicellarial head. It consists of two valves and a basal piece. Muscular bundles are anchored on these skeletal ossicles. The straight pedicellariae have two pairs of adductor muscles (the inner and the outer adductors) and one pair of abductor muscles, these latter being weakly developed. Longitudinal muscle fibers occur all along the stalk of straight pedicellariae. The crossed pedicellariae have two pairs of adductor muscles (the distal and the proximal adductors) and two pairs of abductor muscles (the distal and the proximal abductors). The proximal adductors of crossed pedicellariae are homologous to the stalk muscles of straight pedicellariae.The pedicellariae are able to react to direct and indirect tactile stimuli. There is a great deal of individual variation among pedicellarial responses. Moreover, the reactions occur at random and lack coordination. The seemingly aberrant behavior of the pedicellariae is interpreted as a preventive activity that protects the asteroid body surface against unwanted materials and organisms.     

Anatomy of the ovaries of the starfish Asterias rubens (Echinodermata)

Summary The ovaries of the starfish Asterias rubens were studied histologically and ultrastructurally. The reproductive system in female specimens consists of ten separate ovaries, two in each ray. Each ovary is made up of a rachis with lateral primary and secondary folds: the acini maiores and acini minores. The ovarian wall is composed of an outer and an inner part, separated by the genital coelomic sinus. The ovarian lumen contains oocytes in various phases of oogenesis, follicle cells, nurse cells, phagocytosing cells and steroid-synthesizing cells.Oogenesis is divided into four phases: (i) multiplication phase of oogonia, (ii) initial growth phase of oocytes I, (iii) growth phase proper of oocytes I, and (iv) post-growth phase of oocytes I. The granular endoplasmic reticulum and the Golgi complex of the oocytes appear to be involved in yolk formation, while the haemal system, haemal fluid and nurse cells may also be important for vitellogenesis. The haemal system is discussed as most likely being involved in synchronizing the development of the ovaries during the annual reproductive cycle and in inducing, stimulating and regulating the function of the ovaries.Steroid-synthesizing cells are present during vitellogenesis; a correlation between the presence of these cells and vitellogenesis is discussed.     

Nitric oxide (NO) synthase immunoreactivity in the starfish Marthasterias glacialis

The neuroendocrine system of the starfish Marthasterias glacialis was investigated immunocytochemically using antisera specific for rat neuronal, bovine aortic endothelial, and mouse macrophage, nitric oxide (NO) synthases. Immunoreactivity was detected only with the antibodies specific for the neural enzyme, in the ectoneural and hyponeural tissues of the radial nerve cords and in the basiepithelial plexus and endocrine cells of the digestive tract. The pyloric stomach showed more immunoreactive structures than the other digestive organs, with the rectal caeca showing the least activity. Immunoreactive endocrine cells were located in the cardiac and pyloric stomachs and in the pyloric caeca. Co-localization of the enzyme immunoreactivity, and the staining for NADPH-diaphorase, demonstrate the presence of NO synthase in echinoderms. These results provide further evidence that NO is a neuronal messenger of early phylogenetic origin which has been conserved throughout evolution.     

Re-evaluation of the Devonian family Helianthasteridae Gregory, 1899 (Asteroidea: Echinodermata)

Because of their taxonomic and morphologic diversity, the asteroids of the Lower Devonian Hunsrück Slate of Germany are important to both an understanding of the history of the class Asteroidea and to the interpretation of community evolution during the Paleozoic. Helianthaster Roemer, 1863, a large multiarmed Hunsrück asteroid, is redescribed. The Helianthasteridae Gregory is restricted to Helianthaster and Arkonaster Kesling, 1982 (Middle Devonian, Canada); Lepidasterella Schuchert is similar to the other two genera but known specimens are of poor quality and as a result the status of the genus is uncertain. Helianthaster is noteworthy in part because its size, multiarmed state, and presence of pedicellariae suggest certain crown-group genera, yet aspects of the arrangement of the ambulacral column are characteristic of the Paleozoic asteroid evolutionary grade. Neither Helianthaster nor other Hunsrück asteroids appear closely linked to the crown group; instead, functional patterns apparently re-emerged through time, although identification of specific behavior of ancient asteroids is difficult to impossible.      

Salinity effects on arm regeneration in Luidia clathrata (Echinodermata: Asteroidea)

The effect of salinity (20, 25, and 30?psu) on regeneration of two arms of adult starfish Luidia clathrata (n?=?8 per salinity treatment group collected from Pensacola Bay, Florida, USA 30° 20′ N, 87° 13′ W) was examined in a laboratory experiment (November 2009 to March 2010) to test the hypothesis that L. clathrata is adapted to euryhaline conditions found in bays with regards to arm regeneration. Regenerating arm condition (lengths and weights) relative to treatment was 20-psu treatment?<?25-psu treatment?<?30-psu treatment, and non-regenerating arm condition was 20-psu treatment?<?25-psu treatment?=?30-psu treatment. Luidia clathrata is not adapted to lower salinity conditions found in bays with regard to arm regeneration, despite the common occurrence of the species in bays. Lower salinity in bays should reduce the ability of L. clathrata to recover from damage sustained during, or just prior to, low-salinity periods.     

Identification of protein phosphatases-1 and 2A and inhibitor-2 in oocytes of the starfish Asterias rubens and Marthasterias glacialis

Protein phosphatases present in the particulate and soluble fractions of oocytes of the starfish Asterias rubens and Marthasterias glacialis have been classified according to the criteria used for these enzymes from mammalian cells. The major protein phosphatase activity in the particulate fraction had very similar properties to protein phosphatase-1 from mammalian tissues, including preferential dephosphorylation of the beta subunit of phosphorylase kinase, sensitivity to inhibitor-1 and inhibitor-2, inhibition of phosphorylase phosphatase activity by protamine and heparin, and retention by heparin-Sepharose. The major protein phosphatase in the soluble fraction had very similar properties to mammalian protein phosphatase-2A, including preferential dephosphorylation of the alpha subunit of phosphorylase kinase, insensitivity to inhibitors-1 and 2, activation by protamine and heparin, and exclusion from heparin-Sepharose. An acid-stable and heat-stable protein was detected in the soluble fraction of starfish oocytes, whose properties were indistinguishable from those of inhibitor-2 from mammalian tissues. It inhibited protein phosphatase-1 specifically, and its apparent molecular mass on SDS polyacrylamide gels was 31 kDa. Furthermore, an inactive hybrid formed between the starfish oocyte inhibitor and the catalytic subunit of mammalian protein phosphatase-1 could be reactivated by preincubation with MgATP and mammalian glycogen synthase kinase-3. The remarkable similarities between starfish oocyte protein phosphatases and their mammalian counterparts are indicative of strict phylogenetic conservation of these enzymes. The results will facilitate further analysis of the role of protein phosphorylation in the control of starfish oocyte maturation by the hormone 1-methyladenine.     

Secretory Radial Glia in the Ectoneural System of the Sea Star Asterias rubens (Echinodermata)

Previous studies of epithelial nervous systems have focused on the neuronal elements, but generally neglected the origin of neuro–glial interactions. In this study, we use a polyclonal antiserum directed against Reissner's substance to label non-neuronal bipolar cells in the ectoneural part of the radial nerve cord in the sea star Asterias rubens. Ultrastructural results show secretory activity in these bipolar cells. Immunolabelled material is released into the extracellular matrix in the hyaline layer as well as in the region of the basal end-feet. As a first step towards characterising the antigen, a specific protein band of 36 kD was demonstrated with immunoprecipitation. Cells of this type: (1) traverse the epithelium to full extent from the outer surface to the basal lamina; (2) carry a single apical cilium; (3) contain conspicuous bundles of intermediate filament; (4) produce a secretion which is, at least in part, homologous to the Reissner's substance which is produced by a primitive radial glia cell type in chordates. It is concluded that the bipolar cells in the ectoneural part of the surface epithelium of the sea star Asterias rubens are secretory radial glia, which evidently have a common origin to the radial glia which secretes Reissner's substance in chordates.     

Determination of polyamines in digestive and reproductive tissues of adult Asterias vulgaris (Echinodermata: Asteroidea)

1. The polyamines spermine, spermidine and putrescine were extracted from tissues of Asterias vulgaris and quantitated using thin layer chromatography. 2. In the pyloric caeca, mean (+/- SE) levels of spermine, spermidine and putrescine were 138(15), 86(24) and 415(77) nmol/g wet wt tissue, respectively. In the testes, levels were 95(12), 13(6) and less than 6 nmol/g wet wt. In the ovaries, levels were 105(9), 11(0.8) and 15(8) nmol/g wet wt. 3. High levels of polyamines in the pyloric caeca may be related to secretion or excretion in this tissue. 4. We hypothesize that polyamines will be important in the regulation of cellular activity in these tissues during the annual reproductive cycle.