The mating behaviour of the helmet crab, Telmessus cheiragonus, was observed in the laboratory to obtain information of its fishery management and seed production. Females always moulted before copulation and all moulting females copulated with their mates, while males performed precopulatory guarding before their mates moulted. The average duration of precopulatory guarding was 11.8±5.0 SD days. Sex ratios in experimental tanks did not influence the first guarding duration of male but diminished the female's guarded duration under female-biased treatment. Competition among males for females was observed; larger males appeared to have a competitive advantage. Males started copulation in 41.2±10.9 SD min after females moulted and the copulation lasted for 110.6±6.6 SD min. Postcopulatory guarding duration was 4.0±6.6 SD h. Small males tended not to guard and to copulate with females larger than themselves. Common features and differences in mating behaviour between T. cheiragonus and Erimacrus isenbeckii is discussed.

The effects of the multiple autotomy on epibiosis infestation on embryos, on the survival of embryos, and on brooding care behaviour were examined in females of Cyrtograpsus angulatus, a south-western Atlantic intertidal and subtidal crab. The population of C. angulatus in Mar Chiquita, a coastal lagoon, presents a high incidence of limb autotomy. Newly laid embryos of both healthy and autotomized females were immediately colonized by bacteria and filamentous fungi, peritrichid ciliates, and few small animal species, while detritus was accumulated. The periphery of the embryo mass was more infested by epibionts and accumulated more detritus than the central region. Multiple autotomy in female C. angulatus increased the epibiosis and detritus accumulation in embryos and pleopods, decreased the chance of embryos to complete their development. The following behaviours related to brooding care were observed in both healthy and autotomized females: standing, chela and pereiopod probing, abdominal flapping, pleopod beating and maxilliped beating. However, the time devoted to standing and abdominal flapping was significantly higher in healthy and autotomized females, respectively. Brooding care behaviour in non-ovigerous females and in females with early and late embryos, suggests the presence of different signalling systems that trigger them. We propose that multiple autotomy modifies brood care, decreases the success of embryonic development and, consequently, reduces the contribution of autotomized females (approximately 30% of the potentially reproductive females of C. angulatus in Mar Chiquita) to the following generation.

Tributyltin (TBT) leaching from the antifouling paint on hulls of pleasure craft eliminated a population of dog-whelks Nucella lapillus from Watermouth Cove in the Bristol Channel but outside the Cove the number of snails was apparently unaffected. Following the ban on TBT in antifouling paints, the species has recovered most of its former range in the Cove. It is postulated that the recolonization was from a subtidal population of unusually large and elongated individuals. It was observed that it had taken some 13 years to recolonize a distance of 30 metres.

The functional reproductive system of three Mediterranean species of Coralliophilidae (Gastropoda: Prosobranchia), Coralliophila brevis, Coralliophila meyendorffii and Babelomurex cariniferus, was compared with that of Coralliophila squamosa and three Leptoconchus species. Differences chiefly in the pallial section of the female reproductive tract separate the Indo-Pacific genus Leptoconchus from the Mediterranean species, and subdivide the latter into three different anatomical groups. Polyphyly of the genus Coralliophila is suggested. Comparison of the reproductive system of coralliophilids with that of the related Muricidae allows identifying characters of Coralliophila brevis, Coralliophila meyendorffii and Babelomurex cariniferus that are unknown in Muricidae. The comparison also reveals a closer similarity of Coralliophila squamosa with Ocenebrinae, suggesting that this species might represent a less derived evolutionary line within Coralliophilidae. The reproductive system of some individuals of Coralliophila meyendorffii and Babelomurex cariniferus undergoing penis reduction in the laboratory is also studied. It sheds some light in the ontogeny of the female pallial reproductive tract, and provides direct evidence for the existence of protandry in these species.

Ilyanassa obsoleta (Mollusca: Gastropoda) is an abundant inhabitant of salt marshes and tidal flats on the east coast of North America. Populations of this snail may be heavily infected by larval trematodes. Three species were observed in this work, Himasthla quissetensis, Lepocreadium setiferoides, and Zoogonus rubellus. Mostly as single-species infections, all occupy snail tissues as parthenitae that produce cercariae, which are released from the snail to infect the next host. By periodically testing snails for cercarial emission, single-species infections are here shown to persist over six summers and double-species infections are also noted to be long-lived. Among the 32 snails followed, 25 released the same (or no) cercariae throughout observation periods averaging three years. The other seven indicated infection changes, but only two of these are judged to reflect actual changes. The probability that a snail changed infection status in this study is thus 2.1% y−1. Ilyanassa obsoleta individuals, and apparently their trematode infections, can persist for decades. Because species colonize and get evicted infrequently, sets of trematode species infecting I. obsoleta individuals (infracommunities) are concluded to be isolationist in character.

The morphology and growth pattern of male and female blue mussels (Mytilus edulis) from the north Norfolk coast, UK, were studied. In allometric terms, the external shell parameters of females grew faster relative to shell length than those of males. In absolute terms, females also grew more quickly than males for all external shell parameters and for most internal body parts. At a given age, females are therefore larger than males. Females had a higher shell to tissue weight ratio and a relatively heavier foot than males. A discriminant function incorporating age, weight and shell length, width, and height correctly sexed 81% of individuals in the sample from which it was derived. Both natural and sexual selection may be involved in the evolution of sexual dimorphism in blue mussels.

Mussel seed Mytilus galloprovincialis from two origins (rocky shore and collector ropes) was cultivated on a raft (submerged culture) in the Ría de Arousa (north-west Spain) from approximately 20 mm to 60 mm shell length. Absorption efficiencies (AEs) and absorption rates (ARs) of the individuals were recorded in situ throughout cultivation time from November to July (1995–1996). Absorption efficiencies varied according to a multiple model that highlighted the significant effect of quality of natural seston (f as relative organic content), time of culture and origin of mussel seed. Initial AE values were 42 and 34% of the ingested organic material for collector ropes and rocky shore mussels (P<0.01), respectively. These differences remained significant for the first two months of the culture with higher values for collector ropes mussels. A significant relationship AE vs quality of natural seston (f) was observed according to an asymptotic equation: AE=0.82[1[minus sign]e−5.01(f−0.21)] for both sources of seed (r2=0.90). Absorption rate (mg organic matter g−1 h−1) followed a seasonal pattern with low values in winter and higher values in spring–summer as a consequence of better nutritional quality of food resources. Nevertheless, exceptional peaks of organic material from sedimentary origin in January caused an increase of ingested/absorbed organic material despite its low nutritional quality. Differences in AR values between origins of mussel seed referred to the first month under culture, with higher values for collector ropes individuals. Original habitat of mussel seed usually employed in mussel culture in Galicia is responsible for long-lasting effects through physiological changes that the individuals from the rocky shore habitat presented when placed under raft-submerged culture.

The morphology of the cells during oogenesis in Amiantis umbonella (Mollusca: Bivalvia) was investigated from collections made between November 1997 and January 1999. Each stage is described and prominent features noted. A unique arrangement of auxiliary cells around the oocyte is described.

Spatial distribution of the southernmost population of the purple clam, Amiantis purpurata (Bivalvia: Veneridae), was described from systematic survey data (density and local biomass), and was related to environmental variables (depth and sediment). Geostatistical techniques were used to model and map density, and to estimate absolute biomass.

Spatial distribution was highly contagious: half of the population lives at densities up to 240 clams m−2. Higher clam abundance occur only at sites with finer and well sorted sediment and intermediate depth. Even when the demographic structure of the population was composed of three year-classes recruited between 1978 and 1980, local biomass and density exhibited a non-linear relationship between them, and discrepancies between their distributions of frequency, their relationship with depth, and variographic analysis.

The spherical model was fitted to the experimental variograms. Anisotropy was explored and introduced into the model. The resulting map shows the location and extension of the patches in the study area; they conform a fringe where the highest concentrations are oriented parallel to the coast line, interrupted by small shoals. No anisotropism was evident in the variographic analysis of local biomass. The kriged mean was 3369 g m−2; and estimated total biomass was 53,290 tn.

Such differences between density and local biomass seem to be linked to compensatory processes involving biomass, growth and mortality, originated at the scale of individual overlapping neighbourhoods.

An immunological technique has been developed, which discriminates the Pecten maximus larvae among all other species present in different plankton samples from Brest Bay. This tool was used on each plankton sample to target the temporal distribution of the larvae between summer 1997 and summer 1998. The least abundant period for larvae from April to July 1998, was confirmed and also identified P. maximus which would have been very difficult to recognize with only the help of the analysis of prodissoconch shape. Multi micro-cohort larvae principally from April to July 1998 corresponded probably with as many spawning events.

Two species of bivalves, Cerastoderma glaucum and Abra Ovata, typical inhabitants of brackish waters, were found in Vouliagmeni Lagoon. Seasonal qualitative and quantitative samples were extracted from the different types of the substratum during 1997–1998. Overall, 800 individuals of C. glaucum and 2700 individuals of A. ovata were collected and measured and their population structure studied.

The male scaled squid Lepidoteuthis grimaldii hereby reported for the first time, is equipped with a pair of grossly enlarged sabre-like hooks. These unique hooks, found only on males, are without parallel amongst cephalopods. As a sexually dimorphic character, they are more likely to be involved in reproduction than predation.

The effect of thermal stress upon pattern development in Loligo forbesi was investigated. Levels of pattern disruption and pattern asymmetry were measured by examining the chromatophores of hatchlings reared at three constant temperatures (8, 12 and 16°C). Results indicate a strong positive correlation between thermal stress and disruption of embryonic chromatophore pattern. Asymmetry in chromatophore pattern occurs non-directionally and can therefore be described as fluctuating asymmetry.

A model describing the positive correlation between variation in zooid size within bryozoan colonies and the amount of seasonal variation in temperature is tested in Panamanian encrusting bryozoans from contrasting seasonal regimes. Results reveal that in a natural setting the model provides accurate estimates of the level of seasonality experienced by the colonies.

Cryptic lineages were identified within a morphologically uniform group of sea stars distributed from Australia to Japan. Among eight populations, all of which have been referred to Patiriella pseudoexigua, we found seven unique mitochondrial DNA sequences clustered into four distinct lineages. These four lineages formed a monophyletic group in which sister clades were separated by small genetic distances but could be differentiated from each other on the basis of reproductive differences. The four lineages thus appear to be separate but very closely related species. Examination of reproduction in several Queensland populations revealed that one population (Statue Bay) consisted of hermaphroditic intragonadal brooders with live-born offspring while other populations (Townsville, Bowen, Airlie Beach) consisted of dioecious free-spawners with a planktonic larva. The brooded larvae from central Queensland populations closely resembled brooded embryos and larvae of a Japanese lineage, while the planktonic larvae from northern Queensland were similar to the original description of planktonic larvae from a Taiwan population. However, each of the viviparous lineages was more closely related to a lineage with planktonic larval development than the viviparous lineages were to each other. Patiriella pseudoexigua thus comprises at least four species with different reproductive phenotypes in which viviparous brooding appears to have evolved in parallel. Based on previous taxonomic work we propose the following names for these four lineages: the dioecious free-spawner from northern Queensland (including the P. pseudoexigua type locality) is P. pseudoexiguasensu stricto; the viviparous brooder from central Queensland is undescribed and here referred to as Patiriella sp. nov; the dioecious free-spawner from Taiwan is temporarily referred to as Patiriella sp. (a senior name for this species may be P. pentagonus); and the hermaphrodite brooder from Japan should be raised to specific status and referred to by the new combination P. pacifica.

The ability of the ophiuroid Amphiura filiformis to alert conspecifics to the presence of a predator was investigated. Our preliminary findings indicate that intraspecific communication of an alarm signal does not occur and that, ultimately, the motivation for altering behaviour in response to a stimulus is not oriented to the population as a whole

The ontogenetic changes in the diet and dietary overlap of three commercially important rajid species inhabiting the slope and shelf waters of the Falkland Islands were investigated. The white dotted skate (Bathyraja albomaculata) was a specialized amphipod and polychaete feeder. The broad nose skate (B. brachyurops) had a diverse diet, consuming a wide variety of crustaceans and fish. The grey tail skate (B. griseocauda) also had a broad diet but consumed a high proportion of amphipods and isopods (e.g. Serolis spp.). Larger individuals of the latter species were more piscivorous and consumed more squid. The diets of all three species showed a marked variation with ontogeny. Dietary overlap was greatest for smaller animals (<30 cm disk width), after which each species became more specialized in their diets. Smaller animals also showed some differences in depth of distribution, which may be an adaptation to reduce inter-specific competition.

Juvenile anemonefish Amphiprion ocellaris were tested in two behavioural laboratory set-ups for their ability to visually or chemically recognize conspecifics. Individuals of two other species of anemonefish, A. clarkii and Dascyllus aruanus, were also used as test specimens for recognition. The results indicate that juvenile A. ocellaris recognize conspecifics visually rather than by olfaction. This is contrary to their finding mechanism of their host anemone. However, the results also indicate that the juvenile A. ocellaris are neither attracted nor deterred by the presence of conspecifics. This is contrary to the settling mechanisms of the damselfish D. aruanus and D. reticulatus, and of the temperate herring Clupea harengus. Hence the results emphasize the variation of sensory abilities and behaviours in fish larvae and juveniles. It is not an area prone for generalizations.

Morphological development of larval Prolatilus jugularis from Bahia Independencia, Pisco, Peru is described. Two hundred and thirty-two specimens were collected with plankton nets in 2000; a developmental series of 40 individuals (2.5–25.9 mm: recently hatched through transformation) was assembled using morphological features and pigmentation. Prolatilus jugularis hatches at approximately 2.5 mm, notochord flexion begins at ∼5.7 mm and ends at ∼6.9 mm, and transformation begins at an unknown size between 14.2–20.3 mm (probably near 20 mm). Diagnostic features of the larvae include a robust body with large head bearing small preopercular spines that begin to form by late preflexion stage; preanal length just under half of body length early in the preflexion stage increasing to near two-thirds of body length in the postflexion stage; and pigmentation primarily on the snout, opercular region, dorsally on the head and gut, laterally above the hindgut, and on the ventral margin of the tail through early flexion stage. A broad mid-lateral stripe begins to form on the trunk and tail late in the flexion stage and dorsal pigmentation forms on the trunk and tail in the postflexion stage. Pectoral-fin rays are first to begin forming, in mid-preflexion stage, followed by principal caudal-fin rays, then by pelvic-, dorsal- and anal-fin rays which apparently begin to form simultaneously near the end of preflexion stage. The dorsal fin is long and continuous, with III–IV short spines and 27–29 soft rays, the anal fin contains 21–23 rays, the first one or two of which may be spine-like, the pelvic fins, with I spine, 5 rays, are below or slightly in front of the pectorals (18–20 rays), and there are 9+8 principal caudal-fin rays and 36–37 myomeres.

Samples of the widely distributed sand goby Pomatoschistus minutus have been investigated genetically from ten localities in the north-eastern Atlantic, North Sea, western Mediterranean and Adriatic Sea. Levels of genetic diversity and differentiation were assessed with starch (SGE) and cellulose acetate (CAGE) gel electrophoresis for 13 enzyme systems. Genetic differentiation between spatial samples points to a reduction or even absence of gene flow between the Adriatic and the other samples, including the western Mediterranean Sea (pair-wise FST=0.37 and 0.32 for SGE and CAGE respectively). The sample from the Adriatic Sea was clearly differentiated from the other samples at the lactate dehydrogenase loci LDH-A* (SGE and CAGE) and LDH-C* (CAGE). Values for genetic differentiation between Venetian and other sand gobies were of the same order of magnitude as between P. minutus and its closest relative P. lozanoi, suggesting allopatric speciation in the lagoon of Venice. At locations outside the Adriatic Sea, the sand goby has the typical features of a marine fish with a high level of gene flow and a low degree of genetic differentiation.