The naupliar development of the barnacle Balanus spongicola is described, from larvae reared in the laboratory. The planktotrophic nauplii of B. spongicola reached the cyprid stage 11 days after hatching, at 20°C, and only eight days after hatching, at 25°C. Larval development includes six naupliar and one cyprid stage, following the typical pattern of the thoracican Cirripedia. Naupliar stages have a broad pear-shaped cephalic shield with a straight anterior margin and a pair of fairly short posterior spines in stages IV–VI. Dorsal and marginal spines are absent. Frontolateral horns are of medium length, directed forward from stage III. Small teeth on the median labral lobe found in some warm-water species are only weakly pronounced. The arrangement of abdominal spines and larval setation are in the usual balanoid pattern. The larvae of B. spongicola share some features with earlier described nauplii of Solidobalanus fallax, a non-native UK species inhabiting British waters. Balanus spongicola, however, possess more typical balanoid larvae. Its nauplii are more elongated (the cephalic shield is longer than broad). Thoraco-abdominal processes and posterior shield spines in B. spongicola are shorter than those in S. fallax. The abdominal process remains shorter than the dorsal thoracic spine until stage VI in B. spongicola but becomes nearly equal in S. fallax.

The red whelk, Neptunea antiqua (Mollusca: Prosobranchia) is a dioecious prosobranch species with internal fertilization, and lecithotrophic larval development. Sexual dimorphism, sexual ratio, the size and age at sexual maturity, and the annual breeding and hatching periods of this subtidal neogastropod were investigated in the central western Irish Sea. Sexual dimorphism was evident as female whelks were larger in both length and weight. Subtle differences in shell morphology were also detected between the sexes. All samples taken together indicated an equal male to female sexual ratio for the studied population. Size and age at sexual maturity were noted to differ between sexes, occurring at 75–90 mm (shell length), or four to five years in males, and 95–110 mm, or six to nine years in females. Quantitative and qualitative techniques identified an annual spawning period between late spring and early summer. Egg masses containing between 14 and 84 egg capsules were observed attached to the dorsal surface of whelk shells in the succeeding months. An average fecundity of 63·78 juveniles was estimated per egg mass deposited. Juveniles were observed to hatch after 6–7 months in laboratory maintained aquaria, indicating a hatching period from October to January in the Irish Sea.

Loripes lucinalis, a littoral bivalve harbouring endocellular sulphur-oxidizing bacteria within its gills, was studied between September 1991 and September 1992 at the Moulin Blanc beach (Brittany, France). The general macro-anatomy of the gill consists of bacteriocyte channels and cylinders made up of two cell types, namely bacteriocytes and intermediate cells. In addition to the usual assortment of cell organelles, the bacteriocytes contain bacterial cells, electron-dense inclusions and large granular bodies. The bacteria are numerous within the bacteriocyte zone, representing 55±8% of the gill cross-sectional surface area. Acid phosphatase activity is detectable within the gill tissue both in proximity to and within the bacterial cells. The electron-dense inclusions and large granular bodies also stain positively for acid phosphatase suggesting that these bodies represent different phases of endosymbiont digestion. Bacterial lysis may be an important means of providing L. lucinalis with its nutritional requirements. The granular bodies stain positively for acid polysaccharides and the percentage of the gill cross-sectional area occupied by lysed granular zones varied as a function of sampling period. The percentage of total body weight represented by the gill was significantly lower in March compared to September, October and January, all other months being intermediate. The decrease in gill percentages and the levels of gill lysis correspond remarkably well to gamete development.

Allopetrolisthes spinifrons is an ectocommensal crab of the sea anemone Phymactis clematis. The population biology of A. spinifrons in north central Chile was examined between January and December 1996. During 1996, 74% of P. clematis in the rocky intertidal zone hosted at least one commensal crab. In most cases, one sea anemone was inhabited by a single adult crab, either male or female. A few sea anemones hosted two or more crabs, one usually being an adult and the others juveniles or small crabs that just had recruited to the host. The sex ratio of adult crabs was ∼1:1 during most months. Reproduction occurred with similar intensity throughout the year as indicated by the continuous presence of reproductive females. Similarly, recruitment of A. spinifrons occurred throughout the year with the exception of late winter when no megalopae and small juveniles were found on sea anemones. Fecundity of female crabs varied between 121 and 5661 eggs per female (6·9–19·2 mm carapace length) and was significantly higher during the austral winter (July) than during the summer (December). The fact that most sea anemones were inhabited by a single adult crab indicates that hosts may be monopolized by individual crabs. Resource requirements may prohibit adult crabs from sharing a host individual with another large crab, while adult tolerance towards juveniles may facilitate the maintenance of local populations.

The pedunculate barnacle Koleolepas avis is a symbiont of the sea anemone Calliactis japonica, which lives on gastropod shells carried by large hermit crabs, usually Dardanus arrosor. Relationships with the host sea anemone, distribution on the gastropod shell, left–right asymmetry and reproduction of the barnacle were investigated. A larger number of barnacles occurred on shells with greater ‘cylindroid dimensions’ of sea anemones. Distribution of barnacles on shells was not random: assuming the in situ position of the shell carried by the hermit crab (∼45° inclination), there were more barnacles along the lower part of the anemone disk than the upper part. Large barnacles lie on either the left or right sides of their capitula, and those lying on the left side (Type L individuals) tended to occur along the left side of the host, and those on the right side (Type R) along the right side. Barnacles [ges ]0·016 g in wet weight had egg masses, and there was a positive relationship between body weight and number of eggs. Koleolepas avis has both hermaphrodites and dwarf (complementary) males attached to them. Large hermaphrodites tended to have larger dwarf males than smaller hermaphrodites.

This study examined the association pattern of two snapping shrimp species that inhabit burrows at exposed rocky shores of the Chilean Pacific coast. The two species Alpheus inca and Alpheopsis chilensis were frequently found to share the same burrows. In most burrows an heterosexual pair of each species was found. A strong positive correlation between the body length of female and male conspecifics cohabiting in a burrow was found both for Alpheus inca and for Alpheopsis chilensis. Similarly, a positive correlation existed between the mean body length of Alpheus inca and that of Alpheopsis chilensis occurring together in one burrow. Thus, a size-relationship between burrow cohabitants exists both in the intra-specific as well as in the inter-specific association of these shrimps. Most females, regardless of their reproductive stage, were accompanied by males. Within a particular burrow, females of the two species often were in the same reproductive stage, i.e. both were with embryos in a similar developmental stage, or both were without embryos. These data suggest that male and female conspecifics, as well as the pairs of the two species, remain together in the same burrow for relatively long time periods. It is proposed that the intra-specific communication system of snapping shrimp facilitates the development of inter-specific associations, such as the one reported herein.

In order to find the most suitable parameter for measuring the nereidid Laonereis acuta, correlations between total length or weight and eight morphological measurements: width of prostomium and 2nd, 6th, 13th and 19th setigers, length of the prostomium, length through segment 6th and length through segment 13th, were established. The width measurements showed the highest values of r, and were the most reliable indicators of size. Comparisons between weight and morphological measurements showed a similar pattern as well as negative allometric growth.

Samples were collected from six pools in order to examine the distribution, body length, base colour and phenotypic diversity (chromatophore pattern) of Idotea granulosa populations on five different species of algae (Ceramium, Corallina, Chondrus, Fucus and Enteromorpha), on each of two shores. Holbeck (HOL) pools had significantly higher habitat heterogeneity in terms of algal species diversity than did those on the more exposed Filey Brigg (FB). Idotea densities were significantly higher and mean body size significantly smaller on Corallina than the other algal species. Isopods were significantly larger on Fucus. There was no significant difference in base colour frequencies between shores but there was a positive association between the brown base colour and Corallina and the green colour and Fucus.  The commonest chromatophore pattern morph was the granulosa-maculata that occurred in 44% of the isopods sampled and five out of ten chromatophore patterns accounted for <10% of the population. The uniformis morph was rare on both shores. There was no significant difference in chromatophore pattern frequency between the sexes. The lineata-maculata morph and maculata morphs showed a positive association with Corallina and Fucus respectively. There was a significant difference in chromatophore pattern frequency between adults and juveniles. The uniformis and maculata patterns occurred in higher frequencies than expected in the adult population whereas the reverse was true of the granulosa-maculata and lineata-maculata morphs.  A total of 85 different phenotypes were recorded from both shores, with 51 of these being exclusively found in HOL pools. Holbeck pools had a significantly higher isopod phenotypic diversity than did those from FB. There was no significant difference in phenotypic diversity between adult and juvenile Idotea at HOL, however juveniles had a significantly higher phenotypic diversity than did adults at FB. Overall, there was a significant positive correlation between rockpool algal diversity and isopod phenotypic diversity.

The population of Paguristes erythrops (Crustacea: Anomura) was studied based on seasonal abundance, size–frequency distribution, sex ratio and reproductive period (percentage of ovigerous females). Specimens were collected monthly by SCUBA diving in the infralittoral area of Anchieta Island, Ubatuba. A total of 543 individuals was analysed. Animal size (minimum and maximum shield length, respectively) was 1·7 and 11·8 mm for males, 1·7 and 10·3 mm for non-ovigerous females, and 3·2 and 7·8 mm for ovigerous females. The sex ratio was 0·91:1. Sexual dimorphism was recorded by the presence of males in the largest size-classes. The absence of ovigerous females during winter months (June to August) and their high incidence from January to March indicated discontinuity in the reproductive cycle, suggesting that females become ovigerous and breed in the summer, with the spawning period lasting from spring to autumn. This strategy of reproduction probably was based on competition with other coexisting species in this area.

The effects of sublethal tributyltin (TBT) concentrations on the growth and development of Ruditapesdecussatus larvae were studied. Veliger larvae of R. decussatus were exposed to TBT nominal concentrations of 25, 50, 75 and 100 ng Sn l−1 in the water for a period up to 13 d. Larval growth and development were chosen as endpoints for evaluation of TBT toxicity. Growth of R. decussatus larvae was severely affected by TBT concentrations (25–100 ng Sn l−1). A 3- to 6-fold reduction growth was observed in these early larval stages. Furthermore, R. decussatus larvae exposed to TBT did not develop further than D-larvae while the unexposed ones reached the umbonated stage.

This study examined the role of predation in restricting early benthic phase (EBP) lobsters to shelter-providing substrata. In the field, the survival of animals provided with cover in the form of cobble and gravel substrata was significantly higher than unsheltered controls. Small benthic fish, particularly gobies Pomatoschistus minutus and rockling Ciliata mustela were the primary predators subtidally while crabs Carcinus maenus appeared to be the dominant intertidal predator. Predatory attack primarily occurred within minutes of the lobsters being deployed. The study reinforces the role played by predation in restricting EBP European lobsters to shelter-providing substrata.

Commensal and parasitic copepods (Arthropoda: Crustacea: Copepoda) of two common species of sea squirts, Phallusia mamillata and Ciona intestinalis have been investigated in the sea of Taranto (southern Italy).

A total of 2590 specimens of copepods were collected (five families, eight genera and 13 species). The sex ratio on 2582 specimens was 1228 males (47·56%) to 1354 females (52·44%).

The species were identified by the hosts in which they were found, their sex ratio host by host, and the specific variability and affinity analysis by means of the Sørensen index and the diversity index by means of the Shannon application.

Some species of copepods have been found for the first time as in Ciona intestinalis (Hermannella rostrata) and in Phallusia mamillata (Notodelphys canui, Doropygus pulex, Pachypygus gibber, Notopterophorus auritus, Lichomolgus albens, Hersiliodes latericia). The association Notodelphys canui–Doropygus pulex—Notopterophorus auritu–Lichomolgus albens is noted for the first time in the Mediterranean Sea.

The population structure of the deep-sea sponge-associated shrimp Spongicola japonica was investigated, and the mechanism of pair formation analysed from field samples. The composition pattern of shrimp in host sponges was divided into three patterns by sex and number as follows: solitary, a solitary inhabitant; sexually paired, a pair with a male and a female; grouped, multiple individuals excluding those designated as sexually paired. Juveniles usually remained grouped or solitary in a host cavity until the size at which gonadal maturity starts. Before forming sexual pairs, shrimp appear to have a free-living period outside the host, when the ovarian stages of females correspond to early to late vitellogenesis. Re-invasion is just before the first spawning, when females are in the ovarian stage of late vitellogenesis.

Two populations of Clibanarius erythropus from Mediterranean and Atlantic rocky shores were studied to provide data on morphometry, population structure and shell use under different environmental contexts. Hermit crab sex and size were analysed as well as genus, dimension and status of the inhabited shells. A comparison between the two populations gave particular emphasis to the morphological and eco-ethological plasticity of this hermit species.

Three species of microgastropods, Eatoniella atropurpurea, Eatonina rubrilabiata and Amphithalamus incidata, are common in various habitats at mid to low levels on intertidal shores in New South Wales, Australia. These habitats include patches of sediment, pebbles and algal turf. These species are very patchy, varying in abundance within and among habitats at scales of centimetres to many metres. This study describes laboratory experiments which tested hypotheses about differences in mortality and growth rates for each species in three different habitats: sediment, pebbles and coralline turf. There was greater mortality in coralline turf without sediment for E. rubrilabiata and A. incidata, whereas Eatoniella atropurpurea showed a greater mortality in sediment. Moreover, Eatonina rubrilabiata had a faster rate of growth in sediment, whereas Eatoniella atropurpurea grew more rapidly in coralline turf. The different rates of mortality and growth for these species in different habitats provide mechanisms which may partially explain the patterns of abundance in the field.

Responses of the Antarctic limpet Nacella concinna (Mollusca: Gastropoda) to meltwater exposure were studied at Adelaide Island (67°34′S 68°08′W). Limpets in crevices could be bathed in pure meltwater, though animals in large pools often avoided significant exposure to lowered salinity because of marked halocline formation. Small pools containing limpets showed extremely demanding osmotic environments with fluctuations between salinities of 3 and 30 psu being recorded within 1–2 min because of alternating meltwater and wave action. Analysis of haemolymph osmolarities in animals taken from the field demonstrated significant falls in osmolality (to 600–800 mOsm kg−1) compared with control animals living in seawater (1000 mOsm kg−1). A few moribund animals had osmolarities <600 mOsm kg−1. Nacella concinna are stenohaline osmoconformers with a median lower lethal salinity (96 h) of 20·9 psu and a median lethal time for freshwater exposure of 2 h 18 min. A 1 h exposure to freshwater caused a 14% increase in body volume and a 27% loss of body fluid ions. Nacella concinna responds behaviourally to meltwater by short-term, ineffective, clamp down of the shell, retraction of the head, cephalic tentacles and mantle margin tentacles. On vertical surfaces limpets respond actively to freshwater exposure by rapid detachment; 50% of animals lose adhesion within 5 min. Consideration of tidal regimes at Adelaide Island suggests that an individual intertidal limpet has a risk of being exposed to severe meltwater exposure about once per year.

The reproductive biology, in response to temperature, season and copper, of a coastal population of opossum shrimps (Crustacea: Mysidacea) was measured. The reproductive pattern for Praunus flexuosus at Keyhaven (west Solent, southern England) has maximum activity in April and maximum reproductive effort in May/June. Increasing temperature decreases incubation time and the reproductive pattern is adapted to compensate for temperature effects. Reproduction was inhibited with copper exposure. Fertilization of the eggs did not occur in any copper treatment (5, 25, 75, 200 μg l−1 copper added). Brooding females exposed to copper suffered a high abortion rate. The inability to produce broods, appears to be a long-term effect, as specimens previously exposed to copper did not produce any broods after two weeks in seawater controls.

The major by-catch species retained during twice yearly dredge surveys of great scallop, Pecten maximus, and queen scallop, Aequipecten opercularis, (both Mollusca: Pectinidae) populations on 13 fishing grounds in the northern Irish Sea, over a period of five years, were identified and enumerated. Additionally, the damage sustained by the by-catch was assessed and related to a range of physical parameters recorded during the survey. A number of species captured in the spring-toothed dredges exhibited differences in abundance and damage sustained between years, and also between the start and end of the closed season for great scallop fishing (1 June–31 October). The by-catch assemblage varied geographically, dependent upon the underlying community structure, as well as putative factors including gear efficiency and substratum type. Two clear assemblage types were identified by multivariate analysis, one to the south-west of the Isle of Man, the other covering fishing grounds to the north, east and south of the island. There is a hierarchy of species sensitivity to damage in great and queen scallop dredges, probably related to morphological and behavioural characteristics. This selective mortality of a fraction of the community may have long-term implications at the ecosystem level. The degree of damage sustained by many species is related to both the volume of stones retained in the dredge, and the total volume of the catch (dredge fullness). If these were reduced, the overall magnitude of incidental by-catch mortality would be lower.

Burrow morphology and mating behaviour of Upogebia noronhensis was studied using resin casting of burrows in the field and observation of laboratory maintained animals. Burrows of U. noronhensis showed a typical Y-shaped pattern in over 70% of the cases analysed. The remaining 30% comprised U-shaped burrows lacking the lower tunnel (shaft) and burrows with long additional branches projecting from the U portion. Results from animals left to construct burrows in the aquarium closely matched those found in nature. Field and laboratory burrows showed that different shapes are related to the collapse of the burrow walls, the burrowing activities of other individuals and species, and to the behaviour of the species itself. U-shaped burrows form as a result of the partial construction of the burrow (the U part is always built first) or owing to the collapse of the shaft. Burrows with additional branches always belonged to males and result from their search for a female with which to reproduce. This process also produced connected burrows. Mating occurs within the female burrow and this is the only time when two animals occupy the same burrow. After mating, the male returns to its burrow and immediately closes the connection. Larvae are planktonic and probably settle in adult areas, since the smallest juvenile burrows were always associated with adult burrows. This may contribute to the high population densities found in the field (∼200 ind m−2), which in consequence facilitates fossorial encounters for reproduction. This is the first time fossorial encounters for reproduction are reported for an Upogebia species and probably for all Thalassinidea.

Four Benthoctopus species are recognized in the waters of the Falkland Islands: B. eureka, B. magellanicus, Benthoctopus sp. A, and Benthoctopus sp. B. Initial oocyte reserve of B. eureka is 250–535 eggs, the actual fecundity is 75–234 eggs while the rest of the oocytes degenerate at maturation. Larger females have higher fecundity. Gonad maturation of Benthoctopus sp. A and Benthoctopus sp. B follows a similar pattern. The Benthoctopus egg masses contained 170–190 eggs. The hatchlings possess arms that are much longer than mantle length with a large number of suckers, and do not have discernible chromatophores.