Giant larvae: Prolonged planktonic larval phase in the asteroidLuidia sarsi

The bipinnaria larva of the shelf-dwelling asteroidLuidia sarsi Duben and Koren, 1845, can attain (exceptionally) a length of 35 mm; metamorphosis to the adult benthic phase usually occurs well before this size is reached. A seastar rudiment develops at the oral end of the bipinnaria and, under normal circumstances, it detaches itself from its larval body before reaching a diameter of 5 mm. Midwater trawl samples taken from the surface to 1650 m in the Porcupine Seabight during 1978 and 1979, however, includedL. sarsi larvae with post-larval rudiments of 15 mm diameter and greater. It is shown that the bipinnariae and attached post-larvae both continued to grow until a point was reached when it appeared that the young sea-star could no longer be sustained by the bipinnaria. There is evidence that the largest post-larvae had absorbed the bipinnaria tissue and this, it is concluded, is the final stage before enforced settlement. From the estimated growth rate it is likely that many specimens had been in the plankton for >1 yr, giving this species a capability for long-distance dispersal.     

Benthic invertebrate larval response to substrate characteristics at settlement: Shelter preferences of the American lobsterHomarus americanus

The factors controlling shelter selection by the first post-larval stage of the American lobsterHomarus americanus were studied in the laboratory in 1988 using an experimental approach. The relative importance of shelter size, light level within shelters, number of shelter entrances, and presence of algal-film cover in and around them were investigated. Post-larvae showed a strong preference for opaque versus transparent shelters. No difference in post-larval selectivity was observed either for shelters of different widths or heights or between shelters with different numbers of entrances. Post-larvae showed no preference for microhabitats colonized by microorganisms compared to others without colonization. The intensity of the response measured suggests a possible hierarchical organization of the different cues involved in shelter selection, the light level within the shelter apparently being the most important. Simple linear regression was used to assess the effect of shelter area on the number of post-larvae occupying a shelter. Up to four post-larvae were observed simultaneously in a shelter of 40 cm² basal area, indicating that they can cohabit at settlement. The minimum shelter area necessary to the first post-larval stage was estimated to be about 3.25 cm². The results are discussed with reference to recent hypotheses concerning the mechanisms controlling larval settlement in other benthic species with relatively weak mobility during the larval and the post-larval phases.Contribution to the programmes of GIROQ (Groupe interuniversitaire de recherches océanographiques du Québec) and of the Institut Maurice-Lamontagne     

Population structure, growth and recruitment of the euryalinid brittle-star Astrobrachion constrictum (Echinodermata: Ophiuroidea) in Doubtful Sound, Fiordland, New Zealand

The euryalinid brittle-star (snake star) Astrobrachion constrictum (Farquhar) lives coiled around the branches of black coral (Antipathes fiordensis) colonies. Twenty-two vertical transects, 10 m wide by 30 m deep, were swum in Doubtful Sound over a 2.5 yr period from 1993 to 1995. Numbers, disc diameters and colour morphotypes of brittle-stars inhabiting coral colonies were recorded. 36.3% of the coral colonies >200 mm tall (n = 292) hosted ≥1 Astrobrachion constrictum (range 0 to 12). Overall, the population was patchily distributed on the available coral habitat. The dark red colour morphotype of A. constrictum was most common (87%, n = 279) followed by the yellow, striped, and then spotted varieties. The population was comprised mainly of large (≥10 mm disc diam) individuals, and juveniles were rarely encountered, indicating low rates of recruitment or a high mortality of recruits. Disc-diameter data gathered from this and previous studies indicated that growth in A. constrictum is initially rapid, with individuals reaching a disc diameter of 15 mm in ≃2.5 yr; growth decreases with age, as in other deep-sea ophiuroids. Growth rate within years, however, was not constant, with faster growth in the spring/summer. Maximum size for A. constrictum is reached in ≃8 yr at ˜23 mm disc diam. Anecdotal evidence indicates that A. constrictum may not be confined solely to black coral colonies. Received: 25 September 1996 / Accepted: 16 October 1996     

Byssus drifting and the drifting threads of the young post-larval mussel Mytilus edulis

The long, drifting threads secreted by young post-larval mussels (Mytilus edulis L.) are simple monofilaments, distinct in form and function from the attachment byssus threads. The diameters of both thread types are in the micron or sub-micron range but, whereas the attachment threads are of restricted length and terminate in an attachment plaque, drifting threads exceed the post-larva in length by more than two orders in magnitude and are without plaques or any other structures. Transmission electron micrographs of drifting threads show no evidence of internal sub-structure. In contrast, attachment threads appear to be made up of filaments. These studies confirm that the drifting threads are highly effective in enhancing the dispersal of young mussels. The terminal sinking velocity of young drifters is typically ca. 1 mm s^-1. At this velocity the suspension range above the sea bed, assuming given values of vertical diffusivity, is estimated to be 0.5 to 5 m. Calculations of the fluid drag experienced by post-larvae in the water column show that the theoretical viscous drag force on the thread is sufficient to account for the reduced sinking rate of drifters. The calculated contribution of the thread to the total drag is approximately one order of magnitude greater than that of the post-larval body. A rapid thread-deployment strategy, shown by post-larvae which are brought into suspension, may prolong each drifting excursion and thus further enhance dispersal in turbulent marine environments.     

Reproductive biology of a deep-sea brittle star Amphiura carchara (Echinodermata: Ophiuroidea)

 New information on the brooding reproduction of Amphiura carchara, and previous studies of several deep-sea congeners, contradict the prevailing notion that direct development is exceptional among deep-sea echinoderms. Over 500 specimens of A. carchara from 2,850 to 4,100-m depths off the coast of California, USA, were studied. The species was found to be gonochoric, although most brooding species of ophiuroids are hermaphroditic. Females each brooded up to 72 embryos at a time, with up to 10 in a single bursa. The embryos of individual adults were often at different stages of development, but those brooded in a single bursa tended to be at the same stage. Thus, the species has characteristics that breach the distinctions between sequential and simultaneous brooding exhibited by shallow-water ophiuroids. The embryos developed from yolky eggs that are large for an ophiuroid, with the mean largest oocytes 0.45 mm, and ranging to 1.28 mm in diameter. Almost all late-stage embryos were positioned with their mouth and arms pressed against the wall of the bursa, possibly to facilitate the uptake of nutrients from the parent. Thus, A. carchara may be matrotrophic. The largest embryos examined had a rudimentary disk skeleton, and arms with four joints and a terminal plate. Emerging juveniles probably differ in disk diameter. The species appears to brood year round, although differences in gonad size, the incidence of brooding, and the relative numbers of early developmental stages in summer and winter samples indicated that there are seasonal trends in reproduction. Received: 14 February 2000 / Accepted: 3 July 2000     

Settled,symbiotic, then sexually mature: adaptive developmental anatomy in the deep-sea,chemosymbiotic mussel Idas modiolaeformis

The Bathymodiolinae are pervasive in reducing environments in the deep sea, yet data on post-larval and juvenile development and on the process of symbiont acquisition remain elusive. To understand how these opportunistic metazoans survive in ephemeral reducing habitats, individuals of the small bathymodiolin, Idas modiolaeformis, were examined histologically to trace their reproductive development, and with fluorescence and transmission electron microscopy to identify patterns of infection by their environmentally acquired bacterial symbionts. A size series of these mussels was retrieved from larval colonisation devices containing vegetative substrates, deployed for 51 weeks (November 2006–2007) in the central ‘Pockmarks’ region (site 2A) of the Nile deep-sea fan in the eastern Mediterranean (NDSF), a zone where methane seepage can occur (N 32° 31.97, E 30° 21.18, 1,693 m deep). Developmental patterns of germ cell migration, size at first maturity, and symbiont acquisition and localisation are presented for the post-larva to adult transition. The smallest mature adult was a male with shell length (SL) 2.35 mm. All larger individuals in the series were male (maximum SL 6.54 mm). Based on the absence of bacterial signals, plantigrades were asymbiotic, indicating strict heterotrophy in larvae and early post-larvae. During the early stages of dissoconch deposition, extracellular symbiont infection was non-specific. This was followed by increasing specificity on non-ciliated gill epithelia in adults. These observations on early development in I. modiolaeformis represent evolutionary adaptations to their ephemeral, reducing habitats.     

Preliminary rearing experiments on the larvae of Sergestes lucens (Penaedia,Natantia, Decapoda)

Sergestes lucens Hansen, a mesopelagic shrimp fished commercially in Suruga Bay, Japan, was successfully reared from egg to post-larval stage V under laboratory conditions. Chaetoceros ceratosporum and Artemia nauplii were found to be satisfactory food in the laboratory during rearing. Growth, mortality, food preference, and feeding and swimming activities during the various developmental stages were investigated. Temperature changes greatly affected the speed of development and the mortality of the larvae. The optimum temperature range for larval development was 18° to 25°C. The growth rate (length) of larval stages was as rapid as 0.16mm/ day at 20 °C and 0.21 mm/day at 23 °C. The larvae first started feeding on phytoplankton at elaphocaris stage I, and then gradually became predators in the post-larval stages. It is suggested that the critical period for the species occurs in the elaphocaris stages. Environmental data, vertical distribution of the species, and data obtained from laboratory experiments suggest that the fluctuation in the abundance of S. lucens is greatly influenced by the water temperature at around 50 m from June to August. Feeding mechanisms observed in the post-larval stages are described.     

Reproduction,development and population biology of the Caribbean ophiuroidOphionereis olivacea,a protandric hermaphrodite that broods its young

Reproduction and development of the ophiuroidOphionereis olivacea H. L. Clark, a species that broods its young, were investigated in Florida from January through December 1985 and in Belize in June 1985 and April 1986.O. olivacea has a maximum disc diameter of 5.2 mm and is a protandric hermaphrodite. Sex reversal occurs at disc diameters ranging between 2.2 and 4.0 mm; it has 400 µm diameter oocytes and is ovoviviparous. As expected from an obligate out-crosser, this ophiuroid has a similar allocation to male and female reproduction, in terms of gonad volume. Reproduction of the Florida population was monitored for one year.O. olivacea is a sequential brooder and incubates its young during the coldest months of the year. The females produce a single clutch of juveniles each year. Spawning starts in November and peaks in January and February. The ova are spawned synchronously from all the ovaries of each female into the bursae and are retained there. Fertilization is accomplished by intake of sperm into the female bursae.O. olivacea develops through a ciliated embryonic stage that appears to be a modified vitellaria larva lacking ciliary bands. These modified larvae swim in seawater in the bursae. Direct development in this species has resulted from heterochrony in the loss of ophiopluteus features. The number of brooding females in the population increases in November and reaches a maximum in March. JuvenileO. olivacea emerge from the bursae at a disc diameter of 480 µm and each arm has three segments. Recruitment was first detected in April, and juveniles were particularly abundant in June. Small size inO. olivacea is associated with paedomorphic heterochrony with precocious maturation of the males at a disc diameter of 1.5 mm, ~2 mo after taking up their free existence. Brooding as a life history mode inO. olivacea is examined and the adaptations of this species to its warm-water habitats are discussed.     

Population structure of the Spanish sardine Sardinella aurita: natural morphological variation in a genetically homogeneous population

The importance of larval dispersal in determining the distribution and abundance of benthic marine organisms is well recognized; however, the contribution of post-larval dispersal has not been measured. I compared the dispersal of swimming larvae with that of rafting colonies in a population of compound ascidians, Botrylloides sp., living attached to leaves of the eelgrass Zostera marina in Tomales Bay, California, USA in 1990–1992. Colonies rafting on broken eelgrass traveled over 200 times farther and had comparable recruitment success relative to swimming larvae. The recruitment of rafting colonies into new habitats was facilitated by the ability of thesecolonial animals to grow asexually onto surrounding substrata. Rafting colonies brooded larvae that were subsequently relased after the colony settled into a new habitat. These results suggest that colonization of new habitats can occur by post-larvae as well as larvae, and that long-range dispersal by species with short-lived larvae may occur by post-larval rafting.     

Biomineralization markers during early shell formation in the European abalone <Emphasis Type="Italic">Haliotis tuberculata</Emphasis>, Linnaeus

Larval shell formation was investigated in the European abalone Haliotis tuberculata. Stages of mineralization as well as enzymatic and endocrine biomarkers were monitored throughout larval development, from hatching to post-larval stages. Polarized light microscopy and infrared spectroscopy analyses revealed the presence of crystallized calcium carbonate arranged in aragonite polymorphs from the late trochophore stage. A correlation between the main steps of shell formation and enzymatic activities of alkaline phosphatase and carbonic anhydrase was seen. The variations of these biologic activities were related to the onset of mineralization, the rapid shell growth, and the switch from larval to juvenile shell following metamorphosis. Furthermore, a strong increase in the level of calcitonin gene-related molecules was measured in post-larvae, suggesting that endocrine control takes place after metamorphosis. The changes measured for the three biomineralization markers together with mineralogical analysis allowed us to correlate physiologic mechanisms with early steps of abalone shell formation.     

Growth,production and ecological significance of Ophiura albida and O. ophiura (Echinodermata: Ophiuroidea) in the German Bight

Growth and production of the shallow-water ophiuroids Ophiura albida and O. ophiura were investigated at two stations in the German Bight from 1988 to 1991. Growth rings visible on the vertebral ossicles of the ophiuroid arms were interpreted as annual age markers. A correction for overgrown first rings allows for more exact estimations of growth and age. In both species growth could be described by Von Bertalanffy growth functions with the asymptotic disc diameter D =10.1 mm, K=0.229 and t _o=-0.192 in O. albida and D =27.7 mm, K=0.084 and t _o=0.042 in O. ophiura. Somatic production was calculated from mass specific growth rates. Annual production:biomass (P:B) ratios were estimated at 0.32 for O. albida and 0.43 for O. ophiura.AWI Publication Number: 618     

Ontogeny of diet shifts by a microcarnivorous fish, Cheilodactylus spectabilis : relationship between feeding mechanics, microhabitat selection and growth

The mechanisms leading to ontogenetic shifts in prey selectivity are examined for the temperate microcarnivore Cheilodactylus spectabilis (Cheilodactylidae) in north-eastern New Zealand. These fish prey on invertebrates associated with benthic turf and foliose algae, using a suctorial feeding mode combined with oral sorting. All sizes of fish feed in the same shallow-water habitat using the same feeding mode. Dietary analysis revealed that while all sizes of fish consumed similar taxa, the relative proportion of taxa consumed reflected fish size. Juveniles consumed mainly gammarid amphipods while large adults targeted ophiuroids, with an abrupt shift from feeding predominantly on amphipods at 250 mm standard length. This dietary shift loosely coincided with the onset of sexual maturity and a change in growth trajectory, although dietary trends did not differ between sexes. Both juveniles and adults were found to select particular taxa from the available turf micro-fauna, with juveniles consuming smaller sizes of amphipods than adults. Microhabitat use was also found to change ontogenetically. Detailed observations on feeding mechanics suggested that size-related changes in suctorial force allowed the exploitation of a broader range of microhabitats with increasing fish size. Received: 20 June 1997 / Accepted: 1 April 1998     

Selection of substrata by seaweeds: Optimal surface relief

Artificial substrata allow one to test a single factor in a complex environment. We wanted to determine whether surface particle size could regulate settlement and growth in marine macroalgae. Three grades of discrete monolayers of hard particles differing only in diameter (0.1 to 0.5 mm, 0.5 to 1.0 mm, 1.0 to 2.0 mm) were cemented to the surfaces of three quadrants on acrylic discs while the fourth was left smooth. All surfaces were painted with dissolved plastic to ensure chemical uniformity. At different times of the year, 25 plates were bolted directly to basement rock in the low intertidal zone on an exposed coast at the mouth of Narragansett Bay in Rhode Island (Fig. 1). Thirteen conspicuous species of macroalgae colonized the coated acrylic plates during the course of this investigation. Of these, the most abundant were Chondrus crispus, Corallina officinalis, Polysiphonia harveyi and Ulva lactuca, which were observed throughout the program. Initial settlement did not differ significantly among the experimental surfaces, but with time patterns in the distribution of these algal populations correlated with the surfaces beneath them. These differences were visually striking and not the same for each species. Most of the Chondrus crispus (79.5%) and U. lactuca (85.2%) appeared on the two largest particles, but only for C. crispus was the difference in populations within these grades significant (P<0.05). Populations were considerably smaller on the smallest grade (20.1 and 13.8% respectively), and on the smooth quadrants only a few individuals of these two species appeared (0.5 and 1.0%). The number of plants of P. harveyi, on the other hand, did not differ on the three particle sizes tested, but on the smooth surfaces only 2.9% appeared. Corallina officinalis showed optimal development on the smallest grade (44.8%). On smooth surfaces, where 8.4% of its population was observed, no upright articulated portions developed. The season during which the substrata were introduced altered the patterns of development. C. officinalis was the first macroalga to be seen in late spring, but on plates set out in the fall this species did not appear until the following late spring. P. harveyi covered some discs in fall, spring and summer, and on these surfaces Chondrus crispus was delayed up to 1 year. By the end of the experimental period (15 months), C. crispus was the most conspicuous macroalgal species on most of the plates.     

The gastropod statolith: a tool for determining the age of<Emphasis Type="Italic"> Nassarius reticulatus</Emphasis>

The microstructure, shape and appearance of the growth rings in statoliths of Nassarius reticulatus (L.) were investigated. This species possesses two statocysts, each containing a single spherical statolith of calcium carbonate of up to 0.22 mm in diameter in the largest animals. The relationship between statolith diameter (SD) and total shell height (TSH) is exponential [ln(TSH)=26.3SD–0.842], although the function is site specific. Statoliths of the largest whelks (>29 mm) contained three or four clearly defined rings, corresponding to TSH values of ~1.1, 4.6–5.3, 12.0–13.5 and 18.5 mm, respectively. The first ring likely represents the metamorphic ring that was deposited at the time of larval metamorphosis when the post-larval whelk adopted a benthic lifestyle. The estimated size of the whelks at formation of the second, third and fourth statolith rings closely matched the TSH inferred from the shell rings. It is concluded that the patterns of growth rings present in statoliths can provide information about the age and growth of N. reticulatus.Communicated by O. Kinne, Oldendorf/Luhe     

Frequency of sublethal injury in a deepwater ophiuroid, <Emphasis Type="Italic">Ophiacantha bidentata</Emphasis>, an important component of western Atlantic <Emphasis Type="Italic">Lophelia</Emphasis> reef communities

The occurrence and relative abundance of tissue (arm) regeneration in the ophiuroid, Ophiacantha bidentata (Retzius), was examined in individuals collected primarily among colonies of the deep-water coral Lophelia pertusa off the southeastern United States. Seven deep-water coral sites (384–756 m), located between Cape Lookout, NC, and Cape Canaveral, FL, were sampled in June 2004 using a manned submersible. The presence of regenerative tissue was evaluated by visual inspection of each individual ophiuroid, and the proportion of regenerating arms per individual was examined relative to size of individual, geographic location, and depth of collection. Ophiacantha bidentata, the dominant brittle star collected, commonly displayed signs of sublethal injury with over 60% of individuals displaying some evidence of regeneration. These levels of regeneration rival those reported for shallow-water ophiuroids. Larger individuals (>6.5 mm disc size) had a higher incidence of regeneration than smaller individuals. Size of individual and percent of regeneration were negatively correlated with depth. Although O. bidentata was significantly less abundant in southern versus northern sites, ophiuroid abundance did not appear to be influenced by amount or density of coral substratum. Presence of dense aggregations of O. bidentata indicates that they are an important component of the invertebrate assemblage associated with deep-water coral habitat especially in the northern part of the study area. Assuming that observed frequencies of injury and subsequent regeneration represent predation events then dense ophiuroid aggregations in deep-water coral habitats represent an important renewable trophic resource within these communities.     

Feeding ecology of Liocarcinus depurator (Decapoda: Portunidae) in the Ria de Arousa (Galicia,north-west Spain): effects of habitat,season and life history

The diet of the portunid crab Liocarcinus depurator (L.) in soft-bottom areas of the Ría de Arousa (Galicia, north-west Spain) was studied by analysis of stomach contents, and by comparison of habitats of contrasting abundance, composition and diversity of prey communities. Monthly samples were taken from July 1989 to June 1990 (N=3747) in mussel (Mytilus galloprovincialis) raft-culture areas and central channel zones. Ninety-two food items were identified: crustaceans, molluscs, polychaetes, ophiuroids and fishes were the dominant prey. The raft epifauna and the mussels constituted the dominant group of prey in the raft areas and inner channel station (the epifaunal crab Pisidia longicornis comprised 30 to 52% of the diet), whereas the benthic macroinfauna was the dominant food component in the mid-outer channel (polychaetes constituted 32% of the diet). In the epifaunal community, diet selection for P. longicornis was positive and for amphipods was negative, whereas within the infauna diet selection for bivalves and ophiuroids was positive and for polychaetes negative or neutral. The seasonal importance of P. longicornis and M. galloprovincialis varied in the diet of L. depurator parallel to seasonal activities connected with mussel culture (seeding, thinning, harvesting) that determine the availability of prey from the rafts. Major changes in the composition of the diet related to the life history of L. depurator occurred during ontogeny. In the raft zones, consumption of mussels and fishes increased with increasing body size, while the consumption of Natantia, non-decapod crustaceans, gastropods, polychaetes Pectinariidae and plants decreased with increasing crab size. Maximum consumption of P. longicornis was by L. depurator individuals of intermediate size (15 to 44 mm carapace width). Stomach fullness (measured as dry weight of food) increased with increasing body size, but with negative allometry. During the late pre-moult and early post-moult periods L. depurator did not consume any food; maximum stomach fullness was recorded for the late post-moult and intermoult stages. Female food consumption decreased during egg incubation. Food consumption was greater in autumn and winter than at other seasons; this appears to be related to seasonal changes in reproduction and moulting.     

Divide and broadcast: sexual reproduction in the West Indian brittle star Ophiocomella ophiactoides and its relationship to fissiparity

It is known that asexual reproduction by fission is the dominant mode of propagation in the small (disc diameter <5.0 mm) ophiocomid brittle star Ophiocomella ophiactoides (H. L. Clark). This species is, however, able to reproduce sexually as well. Sexual reproduction occurs throughout much or all of the year in a population of O. ophiactoides at Jamaica. Gonads are often present in recently split individuals, indicating that sexual and asexual reproduction could occur simultaneously. Regeneration of new gonads in the new disc half is underway by the time an individual is competent to split again. Unsexable individuals are significantly smaller than males, which in turn are significantly smaller than females. The unsexable individuals appear to be below a threshold size for gonad production. Fecundity is low, with the largest females producing a maximum of about 7 400 eggs of small (mean diameter 80 m) size. Fertilized eggs develop into planktotrophic ophioplutei which are typical of the larvae of other species of ophiocomid brittle stars in morphology, rate of development and duration of planktonic period. Egg size and larval type for O. ophiactoides are characteristic of brittle stars with the planktotrophic mode of development, but egg number is uncharacteristically low. Fissiparity in O. ophiactoides may have evolved in association with small body size, concomitant low fecundity and a high-risk planktotrophic larva as a means of ensuring reliable recruitment. Available data, although sparse, suggest that this hypothesis may be applicable to fissiparous brittle stars in general. Fission in brittle stars has a broad systematic incidence at the familial level which suggests that it has evolved recurrently. The ability both to divide and broadcast appears to be a useful combination for O. ophiactoides: it can recruit reliably at large size to occupy favourable habitats quickly, but, it can still maintain low level dispersal of larvae which could provide escape from deteriorating habitats and the potential to colonize new habitats.Contribution No. 328 of the Discovery Bay Marine Laboratory, University of the West Indies     

Life history strategy of a southern European population of brown shrimp (Crangon crangon L.): evidence for latitudinal changes in growth phenology and population dynamics

This study provides a comprehensive examination of the life cycle dynamics of the brown shrimp (Crangon crangon L.) in the Mondego estuary, Portugal, a habitat located near the southern edge of the range of this species in European waters. The phenology of all life stages was documented (from the occurrence of ovigerous females, developing embryos, planktonic larvae and benthic post-larvae), and migration patterns of larvae into and out of the estuary were examined. Temperature-dependent functions of egg and larval development were combined with data on field abundance to predict the timing and magnitude of occurrence of larvae and recruits. Compared to brown shrimp at higher latitudes, southern conspecifics grow slower, mature earlier and have smaller brood sizes, and larvae have a more protracted settlement period. The Mondego estuary, besides acting as nursery area, is a dynamic platform for C. crangon to use in different stages, sizes and seasons.     

Cementation vs mobility: development of a cemented byssus and flexible mobility in Anomia chinensis

The mobility of Anomia chinensis Philippi was studied in relation to its byssal development stage. This species shows high mobility even after it begins cementation in its post-larval stage. Juveniles develop a calcified byssus in the post-larval stage and cement to substrata. However, juveniles up to about 10 mm in shell length can relocate by repeating a sequence of formation of the calcified byssus, abandonment of it, locomotion by crawling, reattachment, and recementation. Juvenile anomiids up to 25 mm in shell length also can move, without breaking their byssal attachments, by shifting the center of byssal calcification dorsally. Even an adult can change its orientation by forming a twisted byssus. These possible methods of movement are closely related to five stages of byssal development. Anomiids can use this mobility to seek a preferable position for attachment after initial cementation, or to adjust their orientation, and thus promote higher survivorship. Received: 18 August 1997 / Accepted: 19 July 1998     

Ecological aspects of ophiuroids from the phytal of S. W. Atlantic Ocean warm waters

Nine species of ophiuroids — Amphipholis januarii, Axiognathus squamatus, Hemipholis clongata, Ophiocnida scabriuscula, Ophiactis lymani, Ophiactis savignyi, Ophionereis reticulata, Ophioderma appressum and Ophiothrix angulata —were collected in various habitats from the mid-littoral and upper infralittoral on the northern coast of the State of São Paulo, Brazil. The abundance of 6 species occurring in 28 species of algae was investigated. A total of 220 samples was collected at monthly intervals from April, 1969 to May, 1970. The distributional pattern of the populations, as determined by Mobisita's index, shows aggregation of the ophiuroids. No ophiuroid species was limited to one algal species. Each species prefers certain algal species and/or a different level on the shore. The most abundant species on algae was Ophiactis lymani, with a maximum density of 1,510 individuals/100 ml of algae. Four species of ophiuroids occurred inside sponges. The most abundant species in sponges was O. savignyi, with a maximum density of 1,892 individuals/100 g of dry sponge. Two species of ophiuroids occurred inside the bryozoan Schizoporella unicornis. Feeding observations have shown Axiognathus squamatus to capture its food by mucous nets. Decapod crustaceans fed on ophiuroids in aquaria. The copepod Thespesiopsyllus sp. was found in the body cavity of the 2 Ophiactis species. Simultaneous sexual and asexual reproduction were abserved in O. savignyi.