Arm autotomy in brittlestars (Echinodermata: Ophiuroidea)

Although ophiuroid arm shedding has long been accepted as an example of autotomy, there has been little investigation of the phenomenon to substantiate this. This paper describes the outwardly visible aspects of autotomy and the function of the internal components of the arm during detachment. Observations are focussed on Ophiocomina nigra, some comparisons being made with eight other species.
Ophiuroid autotomy is characterized by its occurrence close to the point of stimulation, its rapidity, and by the pattern of intervertebral muscle separation at the insertions which is constant for a given species. Evidence is presented showing the important role played by the intervertebral ligament. Both this and the muscle insertions are collagenous, and it is suggested that they and the other intersegmental connective tissues facilitate autotomy by undergoing a drastic, nervously mediated loss in tensile strength which enables the animal to part from its arm with a minimum of effort. Comparable properties have been ascribed to other echinoderm connective tissues, and their role in asteroid and holothurian autotomy has been acknowledged, but such a mechanism has not previously been suggested for ophiuroid arm autotomy.     

The fine structure of Comanthus japonica (Echinodermata: Crinoidea) from zygote through early gastrula

The fine structure of the early embryo of Comanthus has been described by scanning and transmission electron microscopy at approximately 20-min intervals from zygote (20 min) through early gastrula (260 min). In normally developing (and presumably monospermic) embryos, some non-fertilizing sperm were invariably trapped in the perivitelline space; this suggests that there is an effective block to polyspermy at the level of the plasma membrane. No trace of a hyaline layer is encountered in the pervitelline space. At first cleavage, which begins unilaterally at the animal pole, the contractile ring filaments are rather thick (50–150 Å) in comparison to those known for other marine invertebrates. From first cleavage through early gastrula, the lateral surfaces of the blastomeres are broadly adherent, and there is an intercellular material, presumably an adhesive, in the intercellular space. The blastocoel first appears during the four-cell stage. From the eight-cell stage through the start of gastrulation, only one opening, the vegetal pore, connects the blastocoel with the perivitelline space. Gastrulation begins at the 50–100-cell stage, while the vegetal pore is still open, and a clearly defined blastula stage is bypassed. Gastrulation is by a novel process, which I have called holoblastic involution. At gastrulation the eight most vegetal blastomeres, which encircle the vegetal pore, shoot out erect, unbranched filopodia for many microns through the blastocoel. The filopodia adhere to the blastocoelic surfaces of the animal blastomeres and contract, pulling the vegetal blastomeres into the blastocoel. The migrated vegetal blastomeres adhere to one another, forming the entoderm in the vegetal region of the embryo; the remaining blastomeres become the ectoderm. Soon after the completion of cell migration, the entodermal blastomeres appear to cast off their contractile microappendages and adhesive membranes into the blastocoel.     

Ultrastructure of Axial Vascular and Coelomic Organs in Comasterid Featherstars (Echinodermata: Crinoidea)

Abstract The spongy body of Davidaster rubiginosa, D. discoidea, and Comactinia meridionalis, is an axial haemal plexus consisting of two structurally similar, but positionally distinct, regions: an oral circumesophageal part and an aboral part which lies lateral to the axial organ. The axial organ is a large axial blood vessel which is infiltrated by hollow cellular tubes lined with monociliated epithelial cells. The spongy body plexus is a tangle of small blood vessels overlain by podocytes and myocytes. The spongy body and the axial organ are situated in the axial coelom, which is confluent with the perivisceral coelom, the water vascular system, and the parietal canals. The parietal canals open to the exterior via ciliated tegmenal ducts and surface pores. The crinoid spongy body is morphologically similar to the axial gland of asteroids, ophiuroids, and echinoids (AOE). Although the axial glands of these three classes of echinoderms are mutually homologous structures, the homology of the crinoid spongy body and the AOE axial gland is questionable because of differences in organization and developmental origin. Alternatively, the crinoid spongy body may be homologous to asteroid gastric haemal tufts, which are podocyte-covered blood vessels suspended in the perivisceral coelom. The functional organization of the spongy body suggests a filtration nephridium and predicts an excretory function. An alternative hypothesis is that the spongy body is a site of nutrient transfer from the blood vascular system to the perivisceral coelom.     

Microscopical Anatomy of the Cyrtocrinid Cyathidium meteorensis (sive foresti) (Echinodermata,Crinoidea)

Light microscopy and scanning electron microscopy of three specimens of Cyathidium meteorensis (order Cyrtocrinida) revealed some special morphological features. The brachial articulation is provided with a long tendon at the aboral side; the entire articulation surface, including the areas where ligaments attach is built up by labyrinthic stereom. The calycinal ossicle lacks any internal vestiges of a pentameric composition; vertical planes with changing stereom direction lie irrespectively of radial or interradial planes. Gut, ovary and testis are histologically inconspicuous, and the location of the gonads inside the calyx is quite unusual. Both sexes develop outer gonoducts which probably are functionally adapted madreporic canals. The coelomic system differs from that of other crinoids in that a chambered organ is completely lacking. Simultaneously, the aboral nervous subsystem has no aboral nerve centre and simply terminates aborally in the ring-shaped commissure. A glandular axial organ is absent, as are typical sacculi. The data are in accordance with two proposals made previously for Holopus rangii, viz., that the animals can feed raptorially, and that cyrtocrinids probably have evolved by loss of aboral calycinal ossicles of ancestors. In part, our observations differ from those in Cyathidium foresti, so we have chosen to use the species name meteorensis which has been considered a synonym of foresti.     

The fine structure of the fertilization membrane of the feather star Comanthus japonica (Echinodermata: Crinoidea)

Scanning electron microscopy reveals that the outer surface of the Comanthus fertilization membrane bears a network of 14 µ high ridges outlining rows of polygonal facets; however, no spines are present. The so-called spines reported previously by light microscopists were simply optical cross sections of the ridges. Transmission electron microscopy reveals that the fertilization membrane has (1) an outer component consisting mainly of dense, granular material, and (2) an inner component consisting mainly of an interlacing network of 50 Å fibers of moderate electron density. Associated with the fibers of the inner component are dense granular rods and dense lentoid discs.     

Haemal and coelomic circulatory systems in the arms and pinnules ofFlorometra serratissima (Echinodermata: Crinoidea)

Summary The haemal and coelomic circulatory systems in arms and pinnules of a stalkless crinoid are described by transmission electron microscopy, and the coelomic topography is revealed by scanning electron microscopy of corrosion casts and peritoneal surfaces. In addition, the route of the coelomic circulation in the living crinoid is shown by injection of carmine particles, and sites of peritoneal phagocytosis are demonstrated by injection of latex beads. The most important morphological findings are: the controversial hyponeural circulation is haemal and not coelomic; peritoneal ciliation is general and not limited to the cells of the ciliated pits; and occur smooth muscle cells occur below the peritoneum. Carmine particles injected into the central body coelom rapidly travel outward toward the arm and pinnule tips via the aboral canals; the particles return to the central body via the subtentacular canals. Latex beads injected intracoelomically are taken up by peritoneal cells throughout the subtentacular, genital and aboral canals. The possible functions of the haemal and coelomic circulatory systems of crinoids are discussed.     

Regrowth of the stalk of the sea lily, Metacrinus rotundus (Echinodermata: Crinoidea)

Sea lilies are critical to understanding the evolution of the echinoderm body plan, because they are the only extant group whose adults possess a stalk, a prevalent feature in the radiation of a number of primitive echinoderm lineages. Extensive crown regeneration ability has been reported in Metacrinus rotundus, but the regenerative potential of the stalk has never been determined in any species of sea lilies. In this study, we show that M. rotundus whose stalks have been completely excised are capable of stalk regeneration. The process is similar to the growth of the original stalk, but much slower, and the regenerated stalks are not morphologically identical to the original stalk. Since stalk regeneration, in contrast to well-studied regeneration events, probably requires little additional activation of morphogenetic programs, we refer to the stalk regeneration phenomenon as "stalk regrowth" to distinguish it as a special form of regeneration. Since specimens whose entire stalk below the basal plates had been removed were able to regrow, the basal plates, and probably the aboral nerve center within them, are essential for stalk regrowth. Sea lily stalk regrowth is described in detail, and the evolution of feather stars is discussed in light of the growth pattern of the sea lily stalk.     

Circumpolar dataset of sequenced specimens of Promachocrinus kerguelensis (Echinodermata,Crinoidea)

This circumpolar dataset of the comatulid (Echinodermata: Crinoidea) Promachocrinus kerguelensis (Carpenter, 1888) from the Southern Ocean, documents biodiversity associated with the specimens sequenced in Hemery et al. (2012). The aim of Hemery et al. (2012) paper was to use phylogeographic and phylogenetic tools to assess the genetic diversity, demographic history and evolutionary relationships of this very common and abundant comatulid, in the context of the glacial history of the Antarctic and Sub-Antarctic shelves (Thatje et al. 2005, 2008). Over one thousand three hundred specimens (1307) used in this study were collected during seventeen cruises from 1996 to 2010, in eight regions of the Southern Ocean: Kerguelen Plateau, Davis Sea, Dumont d’Urville Sea, Ross Sea, Amundsen Sea, West Antarctic Peninsula, East Weddell Sea and Scotia Arc including the tip of the Antarctic Peninsula and the Bransfield Strait. We give here the metadata of this dataset, which lists sampling sources (cruise ID, ship name, sampling date, sampling gear), sampling sites (station, geographic coordinates, depth) and genetic data (phylogroup, haplotype, sequence ID) for each of the 1307 specimens. The identification of the specimens was controlled by an expert taxonomist specialist of crinoids (Marc Eléaume, Muséum national d’Histoire naturelle, Paris) and all the COI sequences were matched against those available on the Barcode of Life Data System (BOLD: http://www.boldsystems.org/index.php/IDS_OpenIdEngine). This dataset can be used by studies dealing with, among other interests, Antarctic and/or crinoid diversity (species richness, distribution patterns), biogeography or habitat / ecological niche modeling. This dataset is accessible through the GBIF network at http://ipt.biodiversity.aq/resource.do?r=proke.     

Fine structure of syzygial articulations before and after arm autotomy in florometra serratissima (Echinodermata: Crinoidea)

Summary About 1 s after appropriate stimulation, arms of Florometra serratissima break at articulations called syzygies that are specialized for autotomy. The fine structure of unreacted and of newly broken syzygies is described. The unreacted syzygy includes (1) ligament fibers consisting of collagen fibrils interconnected by interfibrillar strands and (2) axons filled with presumed neurosecretory granules. The newly broken syzygy includes (1) ruptured ligament fibers consisting of swollen collagen fibrils associated with interfibrillar globules and (2) axons containing few presumed neurosecretory granules, some of which are fixed in the act of exocytosis; moreover, the calcareous skeleton adjacent to the broken syzygy is partly eroded. The observations before and after breaking suggest that the autotomy mechanism may comprise the following sequence of events: rapid neural transmission from stimulation site to syzygy triggers a massive exocytosis of granules from presumed neurosecretory axons; the released neurosecretions (which could include chelating agents, strong acids, proteolytic enzymes or enzyme activators) etch the skeleton and lower the tensile strength of the ligament fibers by weakening the collagen fibrils and/or the interfibrillar material; breakage of the ligament fibers, the major connective tissue of the articulation, is quickly followed by rupture of all the other tissues at the syzygy.     

Catalogue of neritic-benthonic echinoderms (Echinodermata: Crinoidea, Echinoidea, Holothuroidea) from the Cuban Archipelago

This is an updated taxonomic catalogue of neritic-benthonic Echinodermata (Crinoidea, Echinoidea, Holothuroidea) from Cuba, that includes locality, range, habitat and depth where each species is found. The species list is based on the collections of the Oceanology Institute; Havana, and the "Felipe Poey" Museum (Havana University) Specimens for those collections were captured by a variety of field techniques, narcotized with Cloral hydrate, fixed in formalin and stored in 70-80% alcohol. A total of 53 species were recorded (eight Crinoids, 22 Echinoids and 23 Holothuroids), in 37 genera, 19 families and 12 orders. Ocnus suspectus (Ludwig, 1874) and Phyllophorus (Urodemella) occidentalis (Ludwig, 1885) are new records for Cuban waters.     

Development of Cyathidium foresti (Echinodermata: Crinoidea, Cyrtocrinida) from early attached larvae to adult-like juveniles

To date, knowledge about ontogenetic development of crinoids has been exclusively based on comatulid species, since early stages of other crinoid taxa have not been available so far. The authors now present a scanning electron microscopical and light microscopical study on a developmental series of young sessile individuals of the cyrtocrinid Cyathidium foresti. This species displays a developmental type of its own. In some aspects, the early stages resemble the early attached larva of comatulids (e.g. vestibulum, enteric sac, somatocoelomic cavity) but differ clearly in other (e.g. far oral position of hydrocoelomic primordium, pattern of podia formation, early splitting of the roof, absence of chambered organ). Therefore a specific term is proposed for this new kind of larva: cyathidula. Older juveniles are quite similar to adults; the developmental course is direct. Consequently the group of holopodid crinoids to which Cyathidium and Holopus belong, can be concluded to originate phylogenetically from neotenic larvae.     

The fine structure of the embryo during the gastrula stage of Comanthus japonica (Echinodermata: Crinoidea)

The fine structure of the embryo of Comanthus has been described by scanning and transmission electron microscopy at two-hourly intervals throughout the gastrula stage (from the fifth through the fifteenth hours of development). At 5 hr, gastrulation has occurred in the absence of any structure comparable to the echinoid hyaline layer; therefore, at least one important mechanism proposed for echinoid gastrulation cannot occur in this crinoid. At 7 hr, the blastocoelic basal lamina has formed, and all ectodermal and entodermal nuclei contain dense aggregates, which are probably perichromatin fibrils. At 9 hr, the blastocoel contains mesenchyme cells, presumably of entodermal origin. At 11 hr, ciliogenesis has started at the apical surfaces of the ectoderm cells and at the archenteral surfaces of the entoderm cells; many of the newly formed cilia are swollen subterminally. At 13 hr, a conspicuous glycocalyx is beginning to cover the apical ends of the ectoderm cells, and the fertilization membrane is beginning to dissolve from its inner surface. Between 5 and 13 hr, there is a gradual development of a junctional complex associating the apicolateral margins of the ectoderm cells ; the zonula adherens part of the complex appears at 5 hr and is well developed by 7 hr, and then the septate junction part of the complex appears at 9 hr and is well developed by 13 hr. At 15 hr, the blastopore has closed, the ectodermal glycocalyx is fully developed, some mesenchyme cells appear to be differentiating into skeleton forming cells, and the fertilization membrane is in the last stages of dissolution.     

In situ stalk growth rates in tropical western Atlantic sea lilies (Echinodermata: Crinoidea)

Despite their greater familiarity as fossils, stalked crinoids, or sea lilies, remain important components of hard-substrate assemblages at bathyal depths in both tropical western Atlantic and Pacific regions. To determine stalk growth rates, specimens collected along the western margin of Little Bahama Bank using the submersibles Johnson Sea Link I and II were measured, tagged with color-coded cable ties, returned to the sea floor either to the site at which they were collected or to different habitats or depths, and recovered several months to over a year later. This paper examines stalk growth rates in Neocrinus decorus, Cenocrinus asterius, and the subspecies of Endoxocrinus parrae (E. parrae parrae, E. parrae prionodes and E. parrae carolinae) and their variations relative to depth and current flow. Studies were carried out at three different depth sites: 249 m, 372-435 m and 540-576 m. N. decorus produces substantially more stalk per year than any subspecies of E. parrae or C. asterius (10-17 cm y^− 1 versus no more than 3.6 cm y^− 1) but contributes no more than twice as much skeletal volume to the sediment because of its more slender stalk. To examine environmental control of growth, E. parrae parrae was transplanted beyond its local depth range to the habitat at which deeper-dwelling E. parrae prionodes occurs (572 m). E. parrae parrae grew at 0.6 ± 0.4 cm y^− 1 (n = 6) here, significantly more slowly than in 404 m and more slowly than E. parrae prionodes (2.1 ± 0.6 cm y^− 1; n = 4), supporting the hypothesis that these two morphs exhibit distinct growth strategies. Growth rates for E. parrae parrae and N. decorus do not differ significantly between adjacent high and lower current-velocity habitats at the same depth, although both exhibit significantly shorter stalk lengths and crown elevations on raised topography apparently subject to stronger flow.     

Cretaceous and Paleogene Bourgueticrinina (Echinodermata,Crinoidea) of the USSR

The theca and the columnals of twenty-two lateCretaceous species of the genus Bourgueticrinus (including two new species), of one species of the genus Democrinus, of four species of the genus Conocrinus (including one new species) and of one species of the genus Paleobathycrinus known from USSR are figured and shortly described. Biometric reconstructions of stems for B. aequalis, B. bellus, B. danicus, B. fischeri and C. tauricus nov. sp. are given. A new index is used to suggest the relative flexibility of stem. Decrease in dimension and flexibility of the arms in several species take place simultaneously with an increase of stem flexibility. This fact seems to be closely related to environmental changes.     

Morphologically Specialized Sperm from the Ovary of Isometra vivipara (Echinodermata — Crinoidea)

The morphology of the sperm of Isometra vivipara is markedly different from the spherical-headed sperm typical of crinoids in general. The sperm head of Isometra has a flattened, oval shape. In addition to a nucleus, the head includes a lateral acrosome on one flat surface and a lateral mitochondrion on the opposite flat surface. From the latter surface of the sperm head, a tail flagellum arises adjacent to the mitochondrion. The discussion considers the relationships between reproductive habits and sperm morphology in Isometra and other crinoids.     

Late Cretaceous (Santonian-Campanian) sea lilies (Echinodermata,Crinoidea) from the glacial rafts of northwestern Poland

Seven Santonian (Isocrinus? minutus, Tetracrinus jagti, Cyathidium senessei, Bourgueticrinidae indet., Notocrinidae indet., Glenotremites paradoxus, Marsupites testudinarius) and seven Campanian (Nielsenicrinus carinatus, Austinocrinus sp., Bourgueticrinidae indet., Bourgueticrinus cf. constrictus, B. ellipticus, B.? suedicus, Roveacrinina gen. et sp. indet.) crinoid taxa from the Cretaceous glacial rafts of northwestern Poland (near Wolin Island) are described for the first time. The taphonomy and palaeogeographic implications are discussed. The present assemblage differs taxonomically from the crinoid faunules recently described from the glacial rafts of eastern Poland. However, these faunules are similar to crinoids from the autochthonous Upper Cretaceous sediments of southern and eastern Poland (Miechów Trough, Kraków-Cz?stochowa Upland, Middle Vistula River valley). An update of Late Cretaceous crinoids from the Miechów Trough and Kraków-Cz?stochowa Upland is also given.