The chromosomes of Platynereis dumerilii (Audouin & Milne-Edwards) are described here for the first time. A modal chromosome number of 2n=28 was recorded, based on counts conducted on metaphase spreads prepared from 24-h-old larvae. The karyotype comprises seven pairs, each of relatively large median (arm ratio, p/q=l.00–0.59) and submedian (arm ratio, 0.59–0.33) chromosomes. Attempts were also made to band the chromosomes using C-banding and silver staining methods. C-band-positive regions were localized on four chromosome pairs (three median, one submedian). A further two chromosome pairs (both median) were observed to have terminal nucleolar organizer regions (NORs). To our knowledge, this is the first time that these banding methods have been successfully applied to any polychaete species. These results are discussed in relation to the karyotypic variation within the class Polychaeta, and the family Nereidae in particular. A stable karyotype consisting of a moderate number of large and morphologically well-differentiated chromosomes, coupled with the ease of culture under laboratory conditions and short generation time, suggests that P. dumerilii is a potentially suitable model for evaluating marine contaminants for genotoxic activity.

This paper describes the random amplification of polymorphic DNA markers (RAPDs) in Lasaea rubra (Erycinidae: Bivalvia). Present evidence suggests that L. rubra is an asexual species; however, the exact mode of clonal reproduction in this species is still a matter of debate. In this preliminary study, four of the primers used generated polymorphic RAPDs. One primer was able to distinguish between individuals from the same or different crevice population. This same primer also resolved a single band difference between otherwise identical RAPD patterns of a parent and its offspring. No familial differences have been detected in several previous studies using allozyme electrophoresis. This paper suggests that many polymorphic markers could be obtained with this species using the RAPD technique. Population genetic analysis of L. rubra has long been hampered by a dearth of polymorphic markers due to its small size. These findings suggest that this technique has the potential to further the study of population genetics in this asexual species.

Acetylcholinesterase (AChE) activity, a marker of neural differentiation, was histo-chemically localized in embryos and larvae of Mytilus galloprovincialis Lamarck and M. edulis L. (Mollusca: Bivalvia). The results show that: (1) the first AChE-active cells develop as two bilaterally symmetrical, postero-dorsal pioneer sensory neurons and their supporting superficial cells; (2) the pathways of their pioneering longitudinal axons are the same as those of two bilaterally symmetrical nerve cords which differentiate later in a postero-anterior direction; (3) in the conchostoma larva the posterior neurons and their associated superficial AChE-active cells give rise to two ciliary sensory-like organs which are the earliest rudiments of pedal ganglia and primary byssus glands; (4) three pairs of posttrochal gangliar rudiments, most probably visceral, parietal and pleural ganglia, develop on the same longitudinal nerve cords in the trochophore larva; (5) starting from the veliger stage, the presumptive foot rotates on the ventral side and migrates forwards, so that this gangliar chain is bent and the viscero-parietal ganglia become localized dorso-posteriorly to the pedal ganglia; (6) the cerebral ganglia differentiate together with the apical organ and the nerve network of the velum after the first pedal nerve rudiments have been detected.

Age, growth and maturation of Loligo vulgaris were studied by examination of growth increments within statoliths of 294 specimens (mantle length, ML, ranging from 31 to 498 mm) caught on the west Saharan shelf between 1985 and 1988. Maximum age was 335 d (290 mm ML) for females, and 396 d (498 mm ML) for males. Growth rates varied considerably among individuals with a greater range in males. Sexual dimorphism in length was apparent after about 210 d. Males and females diverged considerably in weight, with males reaching a greater weight after about 180 d. Growth in length between 124 and 396 d was best described by a power function, while growth in weight was best described by the Gompertz function. Males started maturing at 180–210 d and mature males ranged in age between 250 and 396 d; while females started maturing at 240–270 d and mature females ranged between 285 and 335 d. Loligo vulgaris hatched throughout the year with two distinct peaks; in winter (December - early March) and summer (June-July). The life cycle of L. vulgaris populations on the west Saharan shelf lasts ~1 y, with large males (>450 mm ML) living slightly longer.

Samples of the squid Loligo forbesi Steenstrup 1856 were obtained from commercial catches and research cruises in the Irish and Celtic Seas from August 1991 until October 1993. Age and growth of L. forbesi were estimated from putative daily statolith growth increment counts and from length-frequency data. Indirect evidence of the daily deposition of growth increments was obtained by counting increments on statoliths from immature female squid from successive monthly modes, during a four-month period when length-frequency growth estimates were high. Female growth estimates from length-frequency analysis (15–30 mm per month) were slightly lower than statolith-based estimates (30 mm per month). Statolith data indicated that both sexes had a life-span of approximately one year and that males grew faster and attained a larger size than females. In both sexes growth was found to be logarithmic over the size range sampled (28–505 mm mantle length). Mean estimated age of mature males and females was 317 and 312 days respectively, with the minimum age at maturity found to be 236 and 241 days. Back-calculations of hatching dates showed an extended spawning season from November to May. Squid hatched in the spring grew faster than those hatched in the autumn and winter. In post-recruit L. forbesi, growth of head, mantle and viscera were approximately isometric with body mass. The digestive gland showed slight positive allometry, whilst reproductive organs showed strong positive allometry.

The reproductive strategies of male and female Loligo forbesi Steenstrup, 1856 were investigated from samples obtained from commercial catches and research cruises in Irish waters. In females maturity increased with size, but in males two modes in the size at maturity were identified, with approximately 40% mature at small size (180–200 mm mantle length), and the remainder mature at >250 mm mantle length. The difference in estimated age of the two modes of mature males was small, so size differences were probably due to different growth rates. Growth and maturation proceeded together in both sexes over much of the life-cycle. The effect of maturation on relative growth of somatic tissues was examined using analysis of covariance and multivariate regressions. In males there was a significant decline in total mass, and in mass of mantle, head and viscera, relative to mantle length with maturation. In females total mass was not significantly affected by maturation, but relative masses of head, mantle and viscera declined with maturation, indicating that energy was diverted from somatic growth to gonad production. Potential fecundity estimates were obtained by counting eggs and ova in the oviduct and ovary of mature females and were in the range 2500 to 10,500 (mean 5800). Fecundity was positively related to mantle length. The ovaries of mature females contained a range of egg sizes and developmental stages, indicating that spawning probably occurs intermittently.

This investigation of the diet of 801 corkwing wrasse (Crenilabrus melops: Teleostei; Labridae) from Galway Bay and a sample of 51 corkwings from Dinard has shown that this species is primarily a carnivorous feeder, taking a varied diet with molluscs and crustaceans predominating. A gradual, size-related dietary shift was apparent, crustacean food being favoured by the younger, smaller fish and molluscan food by older, larger fish. A decrease in niche breadth indicated an increase in dietary specialization with increasing length. Little seasonal variation was observed in the consumption of the major food categories. Feeding intensity, however, was influenced by the sea-water temperature. Non-feeding fish were recorded only between November and March in Galway Bay, and approximately two-thirds of the population examined in February had empty guts. Feeding intensity of males was significantly lower than that of females during the breeding season.

The gut contents of 99 ballan wrasse (Labrus bergylta: Teleostei; Labridae) sampled between April and July in Galway Bay, Ireland and 95 ballan wrasse sampled between April and June in Dinard, Brittany, France were examined. Decapods and bivalves were the major prey categories in both areas, algae and gastropods were also frequently eaten but in much smaller amounts. The volume of the major food categories did not vary significantly with fish length. However, fish longer than 20 cm did consume greater volumes of bivalves than smaller fish. An increase in dietary diversity during the breeding season was observed. Ballan and corkwing (Crenilabrus melops) exploited many of the same food categories but with different emphases. Bivalves, which were major prey of corkwing, were also very important to the ballan captured simultaneously at the same site.

The distribution of 38 nests of loggerhead turtles (Caretta caretta) on beaches on Sanibel and Captiva islands, south-western Florida (26°26'N 82°16'W), and of 70 first digging attempts by green turtles (Chelonia mydas) on Ascension Island (7°57'S 14°22'W), was quantified. For loggerhead turtles on Sanibel and Captiva, nests were clumped close to the border between the open sand and the supra-littoral vegetation that backed the beaches. This spatial pattern of nests was closely reproduced by assuming simply that turtles crawled a random distance above the most recent high water line prior to digging. In contrast, green turtles on Ascension Island clumped their first digging attempts on the uneven beach above the springs high water line, crawling up to 80 m to reach this beach zone.

Alpheus edwardsii Audouin and Alpheus lobidens de Man (Crustacea: Decapoda: Alpheidae) are two intertidal snapping shrimp that burrow in association with rocks. They are morphologically similar and are often found in the same intertidal zone. The competitive exclusion theory states that two co-existing species must partition resources. The partitioning of food items as a resource appears unlikely, as gut content analyses revealed that the two species have similar diets and the relationship of shrimp condition and shrimp density indicates that food supply was not in limited supply. Instead the two species partition the resources of space within the intertidal zone, and shelter. The two species were found to exist largely in isolation from each other. Alpheus edwardsii occurred across much of the intertidal zone. Within this range A. edwardsii were most abundant in substrata with a low proportion (<50%) of mud. These substrata are better suited to their elaborate method of burrow construction. The simpler burrow construction method of A. lobidens allows this species the potential to occupy a wide range of substratum types; however, they were found only in muddy substrata with substantial surface rock cover at tidal elevations of 1.18m above datum or below. The restriction of A. lobidens to this region of the intertidal zone is probably related, in part, to their physiological requirements. In regions of co-occurrence, A. lobidens were significantly smaller than A. edwardsii, and utilized smaller rocks as shelters, thus avoiding direct interspecific competition for this resource. The absence of large A. lobidens from these areas may reflect their ability to procure shelter in competition with A. edwardsii, as behavioural experiments conducted in this study found that A. edwardsii were the dominant competitors for this resource.

The epibiotic communities on locally abundant macroinvertebrates, in particular the brachiopod Liothyrella uva and the limpet Nacella concinna, were examined from depths between 0 and 50 m at Signy Island, Antarctica. The percentage cover by epibionts on Liothyrella increased from <20% on the smallest individuals to >50% on the largest, and decreased slightly with depth. The percentage cover of Nacella by epibionts increased with size of individual over an approximately similar range of values, but in contrast with Liothyrella increased greatly with depth. Cheilostome bryozoans and annelids of the genus Spirorbis formed >90% (by area) of the colonists on Liothyrella and 30–60% on Nacella, the coralline alga Lithothamnion and sponges making up the remainder. The bryozoans, which generally dominated the epibiotic communities, comprised complex associations of species which could be described as either generalists, host-specific epibiotic, low specificity epibiotic or locally abundant background species. Positive associations of both occurrence and abundance were found between some of the bryozoans living epibiotically on the brachiopod Liothyrella. The overgrowth interactions recorded, between the three main epibiotic faunal taxa; sponges, bryozoans and annelids, were essentially hierarchical. Sponges usually overgrew Bryozoa, and Bryozoa overgrew Spirorbis as well as occasion-ally smothering small brachiopods. In four adult Liothyrella death may have been caused by the epibiotic bryozoan Arachnopusia inchoata growing over the gape, so preventing feeding and/or respiration.

The colonization of microscopic organisms, commonly called a biofilm, was examined on fibreglass panels situated intertidally at Quibray Bay of Botany Bay in New South Wales, Australia. Panels were examined by incident light microscopy, measuring percentage cover, and by a computer image analysis technique, measuring optical density. Optical density was positively correlated with and was therefore a reliable estimate of total percentage cover of the biofilm. Optical density has not been used before in this application and, although some drawbacks are discussed, it is a much more efficient sampling method than microscopic examination of panels.

Thalassomonhystera bathislandica sp. nov. (Nematoda: Monhysteridae) was found in abundance in a few gelatinous phytodetritus aggregates collected from the surface of bottom sediments in the north-eastern Atlantic at depths of about 4000 m. The new species resembles T. islandica (De Coninck, 1943), an inhabitant of saltmarshes. Viscous detrital aggregates, including sediment agglutinations made by the nematodes themselves, are perceived as the preferred habitats of nematode species in fluffy surficial muds. It is suggested that physical constraints prevent nematodes from a fast invasion into freshly sedimented, loose detritus deposits.

Population dynamics and production of the spionid polychaete Marenzelleria viridis were studied at Great Sippewissett salt marsh (Massachusetts, USA) for two years. Marenzelleria viridis was the main contributor in biomass and production to the macroinfaunal assemblages of the sandy organic sediments of the marsh. Marenzelleria viridis spawned during the cold part of the year and the appearance of settled larvae on sediments was observed from January to May. The density of M. viridis rose sharply from winter to late spring followed by a striking drop through summer. The estimated mean annual production of M. viridis was 60.0 g dry weight m2 during the first year and 26.3 g dry weight m2 during the second year. The population of M. viridis is affected by different processes during the year. The number of initial recruits seems to be largely governed by meteorological conditions. The numbers of recruits are then affected by competition for resources, and later, as predators become active, predation pressure determines the abundance of the population of M. viridis.

This first description of behavioural interactions between benthic pyjama sharks Poroderma africanum (Chondrichthyes: Scyliorhinidae) and spawning squids Loligo vulgaris reynaudii (Cephalopoda: Loliginidae) was made from underwater video recordings. The behaviours are described and illustrated to show that the sharks searched for squids in egg beds, then rested there partially hidden and immobile. The pyjama sharks at-tempted to ambush the squids when they approached to lay their eggs after they had apparently habituated to the predators. Although normally nocturnal, the pyjama sharks had emerged by day from caves and cracks in the rocky reef to attack the spawning squids, thereby benefiting from an occasionally available resource.

This communication presents the first records of mated female Loligo gahi in Falkland Island waters. In October 1993 fully mature mated female L. gahi were identified in samples taken from the commercial fishery in waters east of Lively Island, East Falkland, at depths of 145–174 m. Spermatophores were found in both the mantle cavity and buccal sites of deposition. These records, combined with past records of spent females, suggest spawning periods in late October/early November and April/May. These concur with two of the three periods of spawning suggested from previous studies of juvenile and adult L. gahi.

The cirri of the digital tentacles of Nautilus pompilius are covered by annular ridges, more pronounced on the oral (adhesive) than the aboral side. On the oral side the epithelium is thicker on the proximal and outer surfaces of the ridges than on their distal surfaces. Prominent electron-dense granules occur in the cells of the thick epithelium, but are absent from the thin epithelium and the epithelium of the aboral surface. These granules contain mucopolysaccharide and may be responsible for adhesion.

The digital tentacles of Nautilus are used for attachment to, for example, prey, the substratum, or the partner's shell during mating. Their general structure and histology have been described by Owen (1832), Willey (1898), Barber & Wright (1969), Fukuda (1987) and Kier (1987). The mechanism of adhesion is still uncertain. Barber & Wright (1969) report epithelial cells of two types: pigmented cells containing pigment granules 0–5–1 µm in diameter, interspersed with a small number of mucus-producing cells which may help with the adhesive process.

The age and population structure of Parablennius sanguinolentus parvicornis (Valenciennes) (Pisces: Blenniidae) from the Azores have been studied. Total length and weight relationships are given for each sex. Age study was based on otoliths readings. The von Bertalanffy growth function was applied to describe the growth in total length with age. At the end of the first year mean (±SD) total length was significantly different in males (7.1 ±1.5 cm) and females (6.1 ±1.2 cm). One-year-old males participate in reproduction as satellites, whereas females do not. The implications of this in early growth rate of the males is discussed. During the two most important months of the reproductive season (i.e. June and July), the sex ratio was significantly biased towards males, particularly in the larger size classes.

Earlier descriptions showed that the community of appendicularians off the British coast was mainly composed of Oikopleura dioica (Appendicularia; Müller, 1846) and Fritillaria borealis (Appendicularia; Lohmann, 1896), rarely by Oikopleura fusiformis (Appendicularia; Fol, 1872) and Fritillaria pellucida (Appendicularia; Quoy & Gaimard, 1833) and exceptionally by Oikopleura longicauda (Appendicularia; Vogt, 1854). Based on weekly samples collected during 1989 at a single station off the coast of Plymouth, we describe the first complete seasonal cycle of appendicularians in this area. The results suggest that rather than being occasional visitors, O. fusiformis, F. pellucida and O. longicauda are consistently present and abundant from mid to late summer. Moreover, the seasonal shifts in structure of the community of appendicularians in the area, as depicted by multivariate analysis, are consistent with those of the more southerly central Cantabrian coast (Spain). This suggests that they are viable populations rather than occasional expatriates from other areas.