Squids (teuthoids) fall into two distinct groups according to their density in sea water. Squids of one group are considerably denser than sea water and must swim to stop sinking; squids in the other group are nearly neutrally buoyant. Analyses show that in almost all the neutrally buoyant squids large amounts of ammonium are present. This ammonium is not uniformly distributed throughout the body but is mostly confined to special tissues where its concentration can approach half molar. The locations of such tissues differ according to the species and developmental stage of the squid. It is clear that the ammonium-rich solution are almost isosmotic with sea water but of lower density and they are present in sufficient volume to provide the main buoyancy mechanism of these squids. A variety of evidence is given which suggests that squids in no less than 12 of the 26 families achieve near-neutral buoyancy in this way and that 14 families contain squids appreciably denser than sea water [at least one family contains both types of squid]. Some of the ammonium-rich squids are extremely abundant in the oceans.

The allometric relationships between shell length and shell breadth, shell height, shell weight, wet tissue weight and dry tissue weight are described for a population of Cerastoderma edule living at a high tidal level in the Dovey Estuary, West Wales. Seasonal fluctuations in standard animal values for shell weight and dry weight are interpreted in terms of the cycles of reproduction and food availability; the dangers associated with the use of wet weight in growth studies are demonstrated. The population structure is described using a combination of length-frequency and growth ring analyses and comprised nine year-classes with overlapping size ranges. The growth of the population was very slow and the relative growth rate was almost constant; associated with this slow, atypical growth pattern was considerable longevity and a small maximum size. The reasons for these characteristics are discussed.

The dry weight condition index and water content of two groups of mussels, one with heavy infestations and the other with mild infestations of Polydora ciliata, were determined over a period of 15 consecutive months. The results were seasonally variable, but for most months the heavily infested mussels had a condition index significantly lower, and a water content significantly higher, than the mildly infested mussels. This suggests that heavy infestations of P. ciliata are associated with reduced flesh content in mussels.

Further analyses of the body components of the two groups of mussels, showed that the mantle tissue of heavily infested mussels was reduced much more than the nonmantle tissue. Since the mantle is the main repository of gametes, this suggests that heavy infestations of P. ciliata might lower the fecundity of mussels.

Predation of the barnacles Balanus balanoides and Elminius modestus by the common dog-whelk, Nucella lapillus was studied in the laboratory. Greater numbers of B. balanoides were taken as prey unless the whelks had been previously subjected to an extensive period of starvation.

Selective predation is discussed in the light of similar studies on Nucella and related predatory species. The effects of prey selection on the competitive interactions of the prey species are also considered.

The method of predatory attack involves either a drilling or a prizing technique. The latter is used predominantly when Nucella attacks E. modestus, whereas drilling is employed to a far greater extent when attacking B. balanoides. Attacks using the drilling technique are usually made at the occludent margins of the opercular valves.

The electrophoretic mobilities of 13 enzymes in two species of Chthamalus, C. stellatus Poli and C. montagui Southward, were compared. These species differed absolutely for eight of the enzymes and exhibited some species-specific allozymes for a further four enzymes. No evidence of hybridization was found. The observed mean heterozygosity was 0087 for C. stellatus and 0179 for C. montagui.

A sample of ‘C. montagui’ from Venice differed from two samples from south-west England in external shell characters and in allozyme frequency for two enzymes. These differences are thought to be the result of a geographical cline rather than a distinct separation of subspecies.

Using light microscope histology and scanning electron microscopy, the secretion, storage and discharge of copious quantities of mucus has been demonstrated in the algadwelling harpacticoid copepod Diarthrodes nobilis (Baird). The mucus is secreted by cells closely associated with large haemocoelomic reservoirs, located in the cephalothorax and urosome, which store the mucus prior to its discharge through large integumental vents (up to 38 μm in greatest dimension). A denned behavioural sequence is recognized whereby the animal utilizes discharged mucus to construct an enmeshing capsule. Late stage nauplii are also capable of capsule fabrication.

The mucus bag presumably, acts as a rich and rapidly degradable substrate to marine prokaryotes and is therefore rapidly colonized; suspended organic and inorganic materials are also trapped by the mucus. Observations on gut contents and browsing activity of capsule inhabitants indicate a direct trophic dependence of D. nobilis on the bacteria and organic agglutinations that adhere to the mucus. Utilization of such nutritive materials supports a ‘mucus-trap’ hypothesis recently proposed as a feeding strategy in meiobenthic nematodes.

The presence in Calanus finmarchicus of the sex hormone oestradiol-17β has been confirmed by gas chromatography-mass spectrometry (GC-MS) using the trimethylsilyl and heptafluorobutyrate derivatives.

Levels of the sex hormone testosterone have been measured by radioimmunoassay in Calanus helgolandicus collected from Plymouth Sound, and in C. finmarchicus captured off the Norwegian coast. Concentrations in C. helgolandicus varied during the year from 150 to 626 fg/animal, accounting for 2.3 to 437 x 10-7% of the lipid content and 10.8 to 64.8 x 10-6%percnt; of the total sterol fraction. The mean level in Stage V C. finmarchicus, captured during spring, was 196 fg/animal.

Testosterone was identified in C. finmarchicus by GC-MS of the tert-butyldimethylsilyl derivative.

The incidence of autotomy is described for a discrete population of Carcinus maenas in the Yealm Estuary over a period of one year. During this time the crabs showed seasonal trends in distribution whereby during the summer months they congregated at the top of the estuary. This seasonal migration up and down the estuary corresponded with peak rates in the rate of change in temperature of the bottom water. Recruitment occurred in June, July and August. Overall, there were more female than male crabs although the ratio varied throughout the year. All sizes and sexes of crabs autotomized limbs but although autotomy increased with the size of the crabs it showed no obvious relationship with other population parameters. Significantly more chelipeds than walking limbs were lost. There were more multiple autotomies than would be expected if autotomy was a random event. Autotomy is shown to be a rare event for sexually mature Carcinus but essential to the survival of immature crabs. The means by which crabs may regulate the incidence of autotomy is discussed.

The life-cycles of Corophium volutator (Pallas) and C. arenarium Crawford in the Dovey Estuary are based on two generations per year. Reproduction is well established by April and although the overwintering generation dies during the summer, reproduction continues until October as a result of the breeding of summer-generation animals. The mean brood size of C. volutator is greater than that of C. arenarium and both species show high levels of egg loss from the brood pouch. Hatching and moulting of the embryonic cuticle take place simultaneously and the initial rupture of the egg membranes is made by spines on the cuticle of the telson of the future free-living animal. These spines persist throughout post-embryonic life.

Adult females of both species show a semi-lunar breeding rhythmicity and, associated with this, adult males show a rhythmic pattern of crawling behaviour. As the tide ebbs during the rising spring tide period, adult males emerge from the sediment and crawl across the mud surface in search of burrows occupied by adult females. It is concluded that copulation takes place in the burrow and not in the water column.

In a study of the breeding biology of Euchaeta norvegica (Boeck), Hopkins & Machin (1977) analysed the placement and frequency distribution of spermatophores on females. They found the number of spermatophores on sampled females to be underdispersed relative to the Poisson distribution and concluded that ‘virgin’ females are more attractive to males than females with spermatophores attached. They fitted the Greenwood & Yule (1920) model but drew no conclusions.

The type of question which may be studied by fitting such a model is whether the attraction of males to ‘non-virgins’ is independent of the time since the first spermatophore was attached and also independent of the number of spermatophores already attached. This problem has been further investigated by fitting a version of the Greenwood & Yule model based on asynchronous recruitment of mature females. This version of the model is fully described in Schweder (1979); in this paper the results and biological implications are discussed.

Malacobdella grossa is recorded from a new host, Cerastoderma edule, and the association appears to be confined to the Shetland Islands. Infection rates were high at five of the seven sites studied and double infections were very common. The commensal population was dominated by large individuals.

Special club-shaped cilia with an expanded tip are seen by both light and electron microscopy on the proboscis of Bonellia viridis in addition to the usual filamentous cilia. Using transmission electron microscopy the club tip is seen to consist of a distally curled axoneme enclosed within a sac-like expansion of the ciliary membrane. The axoneme may describe up to two complete loops inside the membrane sac or may occasionally follow an S-shaped course.

A quantitative analysis of the distribution on the proboscis of both filamentous and club cilia is made. No discrete ciliary tracts are present. However, there is a definite pattern of ciliary density distribution. The cilia are densest on both the dorsal and ventral surfaces of the distal fringe of the proboscis. The dorsal fringe cilia are concerned with locomotion and the ventral cilia with food particle uptake. The club cilia are confined to the terminal lobes and neck region of the proboscis. The dorsal surface of the proboscis posterior to the fringe is virtually non-ciliated. The functional significance of the club cilia is discussed.

Annual population changes of four species of Stauromedusae at Plymouth are described. Three of these, Haliclystus auricula, Lucernariopsis campanulata and L. cruxmelitensis, have one generation in a year; Craterolophus convolvulus has two. The completion of the life-cycle of the four Plymouth species within a year is in agreement with Berril's (1962) studies of three species on the west Atlantic coast and with a reinterpretation of Sars's (1846) observations on Lucernaria quadricomis on the coast of Norway.

During the course of collecting trips made in 1976–8 two anthozoans, the actiniarian Aiptasiogeton comatus (Andres), and the octocoral Cornularia cornucopiae (Pallas) were found in Portland Harbour. Neither species has been previously recorded in British waters. A third species, Isozoanthus sulcatus (Gosse), was collected on the shores of the Gower Peninsula, South Wales. Since this species was last recorded in British waters in 1861 and its true taxonomic status is uncertain it is described here.

Rather little is known of the behaviour of larvaceans, although they are of great importance in the sea as one of the few groups able to exploit the nanoplankton. Of the two larvacean groups, oikopleurids have received most attention: the behaviour of Oikopleura dioica has been studied in detail by Gait (1972, Ph.D. Thesis, University of Washington, Seattle), and some notes on the electrical correlates of behaviour have been given by Gait & Mackie (1971) and by Bone & Mackie (1975) for O. dioica and O. labradoriensis. Much less is known of fritillariid larvaceans and, apart from the brief notes on behaviour by Fol (1872) and by Lohmann (1899) in the course of their classical histological investigations, which were extended by Salensky (1904) and Martini (1909), the only recent investigation of living fritillariids is that of Fenaux (1961) who described the remarkable mode of action of the pyloric cilia.

Large catches of the snake blenny, Lumpenus lampretaeformis, have been made in the inshore waters of the west coast of Scotland. Analysis of these catches confirm the view that this species shows marked seasonal variations in abundance. The species lives for up to 9 years and has a rapid growth rate in the first 2 years. It feeds mainly on meiobenthic organisms, of which polychaetes, harpacticoid copepods, ostracods and nematodes are the most important. The reason for the seasonal variation in catch rate is discussed and it is speculated that it may result from the fossorial habit of the adults and the parental care of the eggs.

In order to gain a general understanding of the problems of fish locomotion and appreciate them in an evolutionary context, it is important that we have information available on the kinematics, hydrodymamics and energetics of the swimming of as wide a range of fish as possible. At present, most of our knowledge of fish locomotion is restricted to the swimming of streamlined, pelagic and nektonic teleosts, capable of high speeds and accelerations, that are either neutrally buoyant or have a buoyancy close to neutral (see Lighthill (1969), Webb (1975), Bone (1975) for reviews).

Sodium orthovanadate added internally is a powerful vasoconstrictor in perfused, irrigated gills of Anguilla anguilla. The anion is active at concentrations as low as 10-7 M and its action is antagonized by β-adrenergic vasodilators such as adrenaline and isoprenaline. These effects are discussed in terms of the known mode of action of vanadate as an inhibitor of (Na+ + K+)-dependent ATPase. The biological and pharmacological effects of naturally occurring vanadate are assessed.

Moreau (1876), Bohr (1894), and Fänge (1953) are among those authors who have demonstrated that the swimbladder walls of certain fish are highly impermeable to gases. This property assists in the maintenance of high partial pressures of gases in the swim-bladder and enables physoclist fish to use the swimbladder as a buoyancy mechanism, often at great depth. It has been shown experimentally that the swimbladder contains a high percentage of oxygen (Fänge, 1953; Kanwisher & Ebeling, 1957) and that this percentage increases with depth in most fish (Scholander & Van Dam, 1953; Scholander, 1954). Diffusion of gas through a tissue increases with increasing partial pressure difference across the tissue (Krogh, 1919). This may be as high as 10–20 atm in inshore gadoids such as the saithe, Pollachius virens (L.) or 50–60 atm in mesopelagic fish (Kanwisher & Ebeling, 1957). Thus low permeability to oxygen is required if the swimbladder is to be used as a buoyancy mechanism at any depth.

Eggs of the capelin, Mallotus villosus, are laid superficially on sandy beaches where they may be exposed to temperatures below –5 °C during tidal emersion. The eggs do not freeze until the temperature of their surroundings falls to a mean of –11.9 °C for eggs at the late blastula stage and –10.6 °C for eggs about to hatch, even though films of sea water covering the eggs are frozen. Newly hatched capelin larvae freeze at a mean temperature of –2.5 °C when the sea water surrounding them freezes, and are probably supercooled at temperatures below this before hatching. Evidence is presented which demonstrates that capelin eggs survive low temperatures by supercooling, and that they can do so in the presence of external ice crystals because the chorion prevents ice penetration and hence seeding of the eggs' internal fluids. The chorion of Mallows is shown to possess an extra secondary layer, like that of the related smelts. The primary function of this outer layer appears to be be concerned with adhesion to sand grains but it seems likely that it also prevents or delays ice penetration.