Samples containing the marine ostracod Callistocythere badia were collected from upper shore rockpools on Filey Brigg, north-east England in order to examine the life cycle and genetic structure of the species. Reproduction occurred during spring/summer after which the adults died; juveniles over-wintered as A-1 instars. No males were ever found during the study. Analysis at three polymorphic loci (Gpi, Pgm and Mpi), showed significant deviations from Hardy–Weinberg equilibrium, and significant linkage equilibrium at and between all loci. The genetic data and absence of males confirm that Callistocythere is an asexual species. There was a significant positive relationship between the number of clones found within a pool and rockpool size, but not with algal habitat heterogeneity.

It is possible to mark octopus (Octopus vulgaris) paralarvae on a massive scale (up to 3500 paralarvae l−1) with 100% marking reliability using alizarin complexone (ALC). The whole statolith is marked and the best results obtained were with concentrations of 60-300 mg l−1 and bath duration of 3-24 h. Taking into account the quality of marking, mortality and ALC costs suggest using from 60 to 200 mg l−1 for 3-6 h. The only treatments causing significant mortalities were 300 mg l−1 over 6 and 24 h.

Specimens of Opisthoteuthis grimaldii were video recorded in a shipboard aquarium and their behavioural traits, such as bottom resting, flat-spreading, web-inversion and ballooning response, were described. Ballooning, as defence response, has been recorded only for cirrate octopod families with an intermediate web (Cirroteuthidae: Stauroteuthidae), and this structure has been supposed to be essential for developing this behaviour. Members of the Opisthoteuthidae family lack an intermediate web, indicating that this is a common defence response in cirrates, expressed in a basic form in the Opisthoteuthidae, offering an illustration of how this behaviour can evolve.

Respiration rates during late embryonic development and hatchlings of Octopus vulgaris were measured at 20 °C. Oxygen consumption rates increased suddenly at hatching, in response to the increase in energetic expenditure due to their constant swimming activity by means of jet propulsion. Estimates indicate that hatchlings consumed three times more oxygen than the embryos at late stages. Chemical composition analysis revealed a relatively high nitrogen content (11%) in O. vulgaris hatchlings with an energy content of 1.09±0.03 J mg dry matter−1. Specific oxygen consumption in unfed O. vulgaris hatchlings reached values around 0.18 nmol O2 μg−1 h−1. It was estimated that the oxygen consumption of a medium-size egg mass of O. vulgaris is approximately twice than the oxygen uptake of the respective brooding female.

This paper reports, for the first time, the existence of external digestion of decapod larvae by the common octopus, Octopus vulgaris (Mollusca: Cephalopoda), paralarvae. Zoeae of three crab species were externally digested, leaving a whole and empty exoskeleton. The attack sequence on these prey is also described, and divided into the same three phases (attention, positioning and seizure) already known for Sepia hatchlings.

Loxosomella tonsoria (Entoprocta: Loxosomatidae) was found associated with the polynoid polychaete Lepidonotus clava collected among the algae and debris scraped from the intertidal level at the rocky shore of Limens (Pontevedra, Spain). New features are added to the original description, together with the first description of its buds. Host specificity of the genus and distribution of this species are discussed.

A description is given of Alcyonidium reticulum sp. nov. (Bryozoa: Ctenostomatida), a smooth-surfaced species found encrusting intertidal stones and on Fucus serratus in south-west Britain. It is distinguished from two superficially similar congeners, A. gelatinosum and A. mytili.

Arm loss in two species of starfish Marthasterias glacialis and Asterias rubens (Echinodermata: Asteroidea) was recorded at eight sites in Lough Hyne, south-west Ireland. There was a significant positive correlation between the density of predators (Luidia ciliaris (Echinodermata: Asteroidea) and Cancer pagurus (Crustacea: Brachyura)) and arm loss in both species of starfish. The results suggest that predators may be responsible for a significant proportion of observed arm loss in these two species of starfish in Lough Hyne.

Seasonal and spatial variations in the distribution and abundance of Ophiothrix fragilis larvae (2-arm to 8-arm stages) were determined from a series of plankton net tows in the Dover Strait in 1995 and 1996. Ophioplutei appeared in the plankton between June and September. Larval population was constituted by ophioplutei from different spatio–temporal origins. A major fraction of the ophioplutei observed in the Dover Strait might come from a population localized southward.

This communication reports on experiments, which studied the variation in competitive performance of juvenile cod (Gadus morhua L.) and their growth rates. The fish were held in groups of five in either summer or winter conditions and tested for their individual response to prey offered sequentially. There was marked individual variability. Fish that took the highest share of prey tended also to be those that took prey earlier than others. In winter conditions these fish were the largest, but in summer conditions size had no effect. There was a positive influence of the indices of competitive performance on individual growth rate but the relationship was not significant

Molluscan biogeographical studies around the British Isles and along the north coast of France have revealed a recurring association between the tube-building polychaetes Sabellaria spp. and two marine snails: the pyramidellid gastropod Noemiamea dolioliformis and the aclid, Graphis albida. Whilst few pyramidellids are considered to be host-specific, the evidence from these studies has shown that living animals of N. dolioliformis are only ever associated with Sabellaria spp. There is also a clear relationship between G. albida and Sabellaria spp. but as yet insufficient evidence that it associates only with these polychaetes.