Comparative Analysis of Two Populations of the Brittle Star Amphiura filiformis (Echinodermata: Ophiuroidea) with Different Life History Strategies Using RAPD Markers

Random amplified polymorphic DNA (RAPD) analysis was applied to individuals of Amphiura filiformis sampled from two geographic locations that have previously been reported to have different life history strategies. Of thirty-one 10-mer RAPD primers screened initially, four were chosen and used in a comparative analysis of A. filiformis individuals collected from Galway Bay (Ireland) and Concarneau Bay (France). The results show much variation within A. filiformis populations. Although there are some rare alleles particular to each population, overall the populations were not genetically differentiated with the methods employed. Analysis of molecular variance (AMOVA) showed that a minimum of 93% of genotypic variance occurred among individuals within populations. The statistical significance of this pattern was supported by permutation tests. F _ST values were not significantly different from and UPGMA cluster analyses based on three distance metrics did not separate the two populations. Received March 18, 1999; accepted September 10, 1999.     

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.     

Effects of variable water motion on regeneration of Hemipholis elongata (Echinodermata, Ophiuroidea)

Abstract. To determine whether increased water motion affects patterns of regeneration in the subtidal burrowing brittlestar Hemipholis elongata (phylum Echinodermata), individuals were subjected to laboratory-controlled turbulence conditions. Half of each replicate aquarium experienced oscillatory (wave-like) turbulence while the other half had no turbulence. Individual brittlestars from which arm-tips had been removed were allowed to burrow and to regenerate. Regenerated arm-tip length and weight were tested for differences between organisms in calm and turbulent conditions. Regenerated arm-tip length differed significantly between control and treatment, but arm-tip dry weight and skeleton/tissue ratio of regenerated arm-tips did not. To quantify plasticity in the skeleton, 15 morphological measurements made on the proximal face of vertebral ossicles (using scanning electron microscopy) were integrated as an index of overall ossicle size. We found a significant difference in the overall size index of the vertebral ossicles between treatments, but could not determine which of the measurements contributed most to the difference. The results indicate that regeneration in H. elongata is a complex process that can be modified by environmental conditions.     

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.     

Global diversity of brittle stars (Echinodermata: Ophiuroidea)

This review presents a comprehensive overview of the current status regarding the global diversity of the echinoderm class Ophiuroidea, focussing on taxonomy and distribution patterns, with brief introduction to their anatomy, biology, phylogeny, and palaeontological history. A glossary of terms is provided. Species names and taxonomic decisions have been extracted from the literature and compiled in The World Ophiuroidea Database, part of the World Register of Marine Species (WoRMS). Ophiuroidea, with 2064 known species, are the largest class of Echinodermata. A table presents 16 families with numbers of genera and species. The largest are Amphiuridae (467), Ophiuridae (344 species) and Ophiacanthidae (319 species). A biogeographic analysis for all world oceans and all accepted species was performed, based on published distribution records. Approximately similar numbers of species were recorded from the shelf (n = 1313) and bathyal depth strata (1297). The Indo-Pacific region had the highest species richness overall (825 species) and at all depths. Adjacent regions were also relatively species rich, including the North Pacific (398), South Pacific (355) and Indian (316) due to the presence of many Indo-Pacific species that partially extended into these regions. A secondary region of enhanced species richness was found in the West Atlantic (335). Regions of relatively low species richness include the Arctic (73 species), East Atlantic (118), South America (124) and Antarctic (126).     

Brittle stars from Southern Ocean (Echinodermata: Ophiuroidea)

The present biogeographic study on the ophiuroid fauna from the Southern Ocean (SO) contains an updated checklist, based on a compilation of all the published information provided for the Antarctic and sub-Antarctic regions as well as the information available in SCAR-MarBIN database. Faunal composition and geographical and bathymetric distribution are included. So far, 219 species have been recorded, of which 126 are endemic to the SO, 76 are exclusive to Antarctic waters, and 30 are exclusive to sub-Antarctic waters. This study corroborated the circumpolar and eurybathic character of the ophiuroid fauna of the SO, but some differences are discussed when considering shelf and deep-sea fauna in the whole SO, or in the Antarctic and sub-Antarctic regions separately. The biogeographic affinities of 17 areas considered in the SO are revised, based on a presence/absence datamatrix of the 219 species. This similarity analysis shows three main groups, two of them including sub-Antarctic areas and one for Antarctic areas. The faunal movement patterns between the main geographical connections have been based on historical site records of each species. These movements have a level of faunal exchange that exceeds that of other Antarctic benthic groups. Such movements are mainly from Antarctic and sub-Antarctic regions to the subtropical waters of South America, and from New Zealand and southern Australian waters to sub-Antarctic areas. In this context, the origin of the ophiuroid Antarctic fauna is discussed.     

Variable tensility of the oral arm plate ligaments of the brittlestar Ophiura ophiura (Echinodermata: Ophiuroidea)

The oral arm plates of the brittlestar Ophiura ophiura L. are connected to lateral arm plates at distal and proximal ligamentous junctions. The distal junction is mobile and is disrupted during arm autotomy; the proximal junction is more rigid and does not participate in autotomy. Aspects of the morphology and mechanical properties of the distal and proximal oral arm plate ligaments have been investigated in order to determine if their tensility is under physiological control. By means of creep tests it was found that elevation of the external potassium (K⁺) ion concentration causes a decrease in the viscosity of the distal ligament which is either transient or continues until rupture intervenes. In forced vibration tests the distal ligament often shows a biphasic stiffening then softening response to excess K ^- ions. Anaesthetics block the softening phase but enhance the stiffening component of this response. This ligament is also softened by repetitive electrical stimuli but stiffened by excess calcium ions and by acetylcholine. The proximal ligament appears to have the capacity for only transient changes in mechanical properties. Both ligaments are penetrated by the processes of juxtaligamental cells whose perikarya are arranged in clusters innervated by hyponeural nerves. These cells are thought to modulate the interfibrillar cohesion of the ligaments. It is concluded that the distal and proximal ligaments are mutable collagenous structures which in their stiffened condition help to maintain arm posture without the need for continuous muscular activity, and that at autotomy the distal ligament undergoes a profound loss of tensile strength which facilitates arm detachment.     

Fine structure of the dorsal arm plate of Ophiocoma wendti: Evidence for a photoreceptor system (Echinodermata,Ophiuroidea)

Summary Three structures in the dermis of the dorsal arm plate (DAP) of the brittlestar, Ophiocoma wendti, appear to comprise a photoreceptor system. The upper surface of the DAP bears transparent, knob-like, microscopic structures which are expanded peripheral trabeculae (EPT) of the calcite stereom. The EPT are part of the photoreceptor system and can facilitate light transmission through the DAP by decreasing light refraction, reflection and absorption that occur at stereom/stroma interfaces. Bundles of nerve fibres located below the EPT are a second component of the system, and may function as primary photoreceptors. The intensity of light impinging on the putative sensory tissue is regulated by the diurnal activity cycle of chromatophores, the third element of the system. During the day the chromatophores cover the EPT and thereby shade the nerve fibres. At night they retract into inter-trabecular channels, uncovering the EPT and thereby exposing the nerve fibres to transmitted light. Thus, the transparent stereom may play a role in photoreception, in addition to its generally recognized skeletal function. Although ciliated cells that may be sensory are present in the epidermis of Ophiocoma wendti, they do not appear to be photoreceptors. Functional analogues of the brittlestar photoreceptor system in other echinoderms are discussed, emphasizing the relationship between photosensitivity and the transparency of the stereom in several classes of Echinodermata.     

Brittle stars (Echinodermata: Ophiuroidea) of the Cooperation Sea,Eastern Antarctica

The brittle stars inhabiting the Cooperation Sea, Eastern Antarctica, are described. Since the publication by Fritz Jensenius Madsen (1967), who completed analysis of the data collected by the British, Australian, and New Zealand Antarctic Research Expedition after Theodor Mortensen, the list of brittle stars has somewhat changed and currently comprises 44 species. It was found that the brittle stars of the Cooperation Sea in their species composition are the closest to the brittle stars of the Weddell and Cosmonauts seas.     

Stereom morphogenesis and differentiation during regeneration of adambulacral spines of Asterias rubens (Echinodermata,Asteroida)

Summary The very first mineral deposits appearing in regenerating fractured adambulacral spines of Asterias rubens are minute polyhedrons that cover the surface of fractured trabeculae. Polyhedrons fuse together forming a fold from which a microspine differentiates. Microspines develop into long linear trabeculae which send out lateral processes at regular length intervals. Lateral processes from adjacent trabeculae fuse together, bridging the trabeculae and giving the regenerate the typical meshwork structure of stereom. Most of the regenerate is built up according to this growth pattern which ensures its longitudinal growth. Simultaneously, the initial fascicular stereom of the stub sends out short radial processes which branch into upward and downward directed subprocesses. The latter fuse with their equivalents located above or below, building up longitudinal rows of stereom meshes. These rows then bridge together by additional branched or unbranched lateral processes, so forming a new stereom layer which progressively covers the whole stub. Up to three new layers of stereom are formed in this way at the stub periphery. These become continuous with the stereom layers of the regenerate by fusion of reciprocal subprocesses, so ensuring the continuity between the stub and the regenerate. In both structures the first stage of mineralization results in an open stereom. Stereom thickening occurs in a second stage of mineralization (that is chronologically separated from the formation of the open stereom) and results in the differentiation of the original stereom fabrics (i.e. fascicular stereom). Regeneration of removed spines starts with the formation of a new spine base made of labyrinthic stereom. The development of the latter mostly relies on short branched and unbranched processes which fuse with each other or with predifferentiated meshes. After completion of its base, the regenerating spine lengthens and thickens similarly to the regenerating fractured spines. The diversity of the stereom growth processes observed in the present work may be reduced to the combination of one to three elementary events, viz. the development of long linear processes, of short unbranched processes and of short branched processes. A survey of the literature allows the suggestion that the implementation of these elementary events is sufficient to describe most types of stereom morphogenesis.Senior research assistant NFSR (Belgium)     

Effects of salinity and feeding on arm regeneration in the starfish Luidia clathrata (Say, 1825) (Echinodermata: Asteroidea)

The aim of this study was to determine: (1) salinity that maximizes arm regeneration in the starfish Luidia clathrata; and (2) if low food consumption or low salinity is the cause of the reduced rate of arm regeneration seen at low salinities.. An estimated salinity of 33 g kg^?1 produced maximum regeneration of two arms in L. clathrata. This salinity is typically greater than that found in bays that are the usual habitat for the species. Equivalent food consumption by L. clathrata in salinities of 20 g kg^?1 and 30 g kg^?1 resulted in greater regeneration in salinity of 30 g kg^?1, suggesting lower food consumption at low salinities is not the primary reason for lower regeneration. Higher food consumption compared to lower food consumption, both tested in salinity of 30 g kg^?1, did not increase regeneration, but resulted in more storage of energy in the pyloric caeca.     

A new genus Squamophis of Asteroschematidae (Echinodermata, Ophiuroidea, Euryalida) from Australia

Squamophis, a new genus of brittle star is described. Two species are included in the genus: Squamophis amamiensis (Okanishi & Fujita, 2009) from south-western Japan and Squamophis albozosteressp. n. from north-western Australia. Squamophisgen. n. is distinguished from the other genera of the family Asteroschematidae by the following characters: each radial shield is single-layered and is completely covered by plate-shaped epidermal ossicles, and the relative length of the longest arm spine throughout the arms is as long as the length of the corresponding arm segment. Squamophis albozosteressp. n. is distinguished from Squamophis amamiensis in having white, slightly domed, plate-shaped epidermal ossicles on the aboral side of the body, the ossicles on aboral and lateral portion of the arms form transverse rows, and the other part of aboral side of disc and basal to middle portion of arms are brown but tip of the arms are light purple.     

Peptidergic and serotonergic immunoreactivity in the metamorphosing ophiopluteus of Ophiactis resiliens (Echinodermata, Ophiuroidea)

Abstract. Antibodies against the echinoderm-specific neuropeptide S1 and against 5HT were used to examine the fate of the larval nervous system during metamorphosis in the ophiuroid Ophiactis resiliens . In contrast to most echinoderms, the onset of peptidergic and serotonergic expression was delayed to the advanced ophiopluteus stage, in particular for 5HT. In advanced ophioplutei, peptidergic immunoreactivity was located in simple fibres associated with the ciliated bands, a stomach nerve ring, and cells along the antero-lateral arms. 5HT immunoreactivity was concentrated in 2 oral ganglia in the adoral projections, located at the posterior rim of the mouth. Clusters of 5HT-positive cells were also found along the antero-lateral arms. The ophiopluteus lacked a serotonergic (or peptidergic) anterior ganglion. In echinoids, holothuroids, and crinoids, anterior ganglia are thought to have a sensory role in settlement and metamorphosis. Given that ophioplutei metamorphose in the plankton and that larval structures degenerate before settlement, the absence of apical ganglia correlates with the lack of a functional role for larval structures in substrate selection and settlement. Although most of the larval nervous system degenerated during metamorphosis, the adoral projections and associated oral ganglia appeared to be incorporated into the juvenile mouth, suggesting a potential role for larval neurons in contributing to oral neuronal structures in the adult. S1-positive neurons and fibres in the rudiment developed de novo and in parallel with development of the epineural canal. This structure gives rise to the primordia of the adult circumoral nerve ring and radial nerves, indicating that differentiation of the adult nervous system begins in the early stages of metamorphosis.     

Development of Amphioplus abditus (Verrill) (Echinodermata: Ophiuroidea): I. Larval biology

A fraction rich in secretory granules was prepared from the pyloric caeca of Asterias amurensis by sucrose density gradient centrifugation. The freshly prepared fraction exhibited no casein-hydrolyzing activity- but showed nine times as much specific activity as that of tissue homogenates after incubation at 37 degrees C for thirty minutes. Electron microscopy showed that the secretory granules were membrane-bound granules measuring 0.5-290 mu in diameter and contained dense and/or light amorphous substances.     

The salinity tolerance of Ophiothrix angulata (Say) (Echinodermata: Ophiuroidea) in latitudinally separate populations

Ophiothrix angulata (Say) from an estuary in South Carolina were less tolerant of reduced salinity than those from an estuary in Florida. Animals from North Inlet, South Carolina, became incapacitated more rapidly after exposure to a reduced salinity, and were less able to recover after return to normal salinity. This difference probably results from the more severe selection for salinity tolerance at Cedar Key, Florida. The Florida estuary has a lower average salinity (25‰) than that in South Carolina (30‰), and has more frequent extended periods of reduced salinity. The two populations are of different color varieties and size; there may be differences in the breeding seasons as well. The South Carolina and Florida populations of Ophiothrix angulata may represent different races.     

Feeding biology of the Antarctic brittle star Ophionotus victoriae (Echinodermata: Ophiuroidea)

Summary The diet and feeding behavior of the brittle star Ophionotus victoriae were studied in 1981–1983. Frequency-of-occurrence and points methods were used to examine stomach contents of 2475 specimens from 19 stations representing seven general localities along the Antarctic Peninsula and South Sandwich Islands. Results of the two methods were in agreement and indicated this species is an opportunistic generalist with high diet plasticity. The most abundant component of the stomach contents was sediment but the diet derived from at least 13 phyla. Crustaceans, notably euphausiids and amphipods, were most important at some locations. Diet composition varied significantly between locations and years, but did not differ among brittle star size groups. Stomach content data and laboratory studies indicate that O. victoriae utilizes a variety of feeding methods but not suspension feeding.