Species of the cyclopoid copepod genus Oncaea are commonly polymorphic. Using material from several localities, forms of O. venusta Philippi, O. mediterranea Claus and O. conifer a Giesbrecht are described, and specimens of two closely related and morphologically similar species, O. ornata Giesbrecht and O. englishi Heron, are compared. The integumental pore signature patterns of all these species are mapped from stained, tissue-free integuments. Each species has its own characteristic pore signature pattern and sexual dimorphism is confined to the urosomal pore pattern. Similarly the prosomal pore patterns of female copepodid 5 do not usually differ from those of adult females, but urosomal patterns are distinct. Juveniles of O. conifera are exceptional in this respect; their prosomal pore pattern lacks the detail of the adult pattern. Differences in the pore signatures of O. ornata and O. englishi confirm their status as separate species. Signatures in the O. conifera ‘group’ may also prove to be distinct. Whereas intraspecific variation in pore signatures may exist at a level below the resolution of this technique, such small morphological differences should be considered to be taxonomically insignificant.

The implications of polymorphism in the process of speciation, and the mechanisms by which the polymorphic forms are maintained are discussed.

Scanning electron microscopy and light microscopy are used to examine the morphology of pores and their associated sensilla. Three types of sensilla are described, peg, short-hair and long-hair sensilla.

Based on the morphology of the mandible, female maxilliped, and male first endopod, Lichomolgus longicauda (Claus) is transferred to Metaxymolgus Humes & Stock, 1972. M. longicauda is recorded for the first time from Sepia officinalis L. taken in British waters.

During five annual ground fish surveys of the North Sea, all the benthic invertebrates trawled at 48 primary stations were recorded. The data were subjected to classification analysis, which showed a basic division between northern and southern North Sea benthos. The southern North Sea was further divided into three benthic regions, and the northern North Sea into four benthic regions (including one to the west of Shetland). The factors influencing the faunal assemblages in the various regions were discussed.

The teeth and grasping spines of Sagitta are similar in structure, both having a central pulp cavity surrounded by two electron-dense chitinous layers. The cells of the pulp cavity contain microtubules arranged along the long axis. The two chitinous tubes are separated by a less-dense zone crossed by coarse fibrils linking the two. The teeth and spines insert into less electron-dense chitin (presumably flexible) and are moved by processes of anchor cells which pass into the basal chitinous zone. The inner region of the anchor cells is apposed to the connective tissue layer on to which the muscles of the teeth and spines insert. At the base of the pulp cavity, i.e. at the secretory zone where the teeth and spines are formed, the cells of the pulp cavity contain electron-dense granules in which zinc is found; zinc is also present in the inner and outer dense chitin layers at high concentration (0·5–1·0% of the dry wt).

Both spines and teeth are tipped with fibrous cones containing silicon. It is suggested that the zinc associated with the chitin serves to toughen the teeth and spines and render them less liable to fracture, and that the silicon in the tips confers hardness to this vulnerable region.

The life-history of hydroids from a mixed population of Tubularia indivisa and ‘T. ceratogyne’, from an intertidal site at Felixstowe, Suffolk, has been studied. Tubularia breed throughout the year, but recruitment is greatest in spring with a smaller peak in late summer. The spring-recruited hydroids are the progeny of T. indivisa, but during the summer they mature as ‘T. ceratogyne’ and breed to produce the T. indivisa that dominate the population in spring. It is concluded, on this evidence, that ‘T. ceratogyne’ is a form of T. indivisa.

In this population T. indivisa suffers from predation by the nudibranch Dendronotus frondosus, and their mortality rate varies from 2% per month in winter to 70% per month in summer. The life-span of T. indivisa is approximately one year, but their mean post-larval life expectancy varies from 30 days (spring recruitment) to 160 days (autumn recruitment). There is no evidence that autotomy of the hydranth is an integral part of the life of T. indivisa.

The behaviour and physiological responses of Mytilus edulis L. to increased concentrations of copperare dependent on the absolute copper concentration present and not the rate of increase of concentration. The sequence of behavioural responses isolating the animal from heightened sea-water copper concentration is similar to that observed in response to lowered salinities. The effects of copper onthe oxygen consumption of intact and ‘propped open’ and animals whose posterior adductor muscles havebeen severed suggest that only measurements of animals in the latter state give a true reflexion of the effects of copper on the oxygen consumption of the tissues of Mytilus. The effects of increased sea-water copper concentrations on the filtration and ventilation activity of mussels are assessed, but consideration of the data in terms of Dejour's equation of gaseous exchangesuggest that indirect measurement of ventilation activity gives rise to differing results. The adaptive advantage of theresponse of Mytilus to heightened sea-water copper concentrations is considered.

The River Tamar and its tributaries drain a highly metalliferous area; and increased metal levels in river water might be expected to affect biological water quality in the estuary. In order to detect possible effects we have used sensitive responses to stress of the hydroid Campanularia flexuosa as an index of quality of water samples from the River Tamar, Plymouth Sound and Cattewater. No water samples caused inhibition of colonial growth rate, but in each experiment there were significant variations in other more sensitive responses. It is these variations that we have related to metal distributions, although of the metals measured, only copper and cadmium occasionally occur in concentrations that could be biologically significant, and at the same time show any correlation with the hydroid responses. The limitation of the survey to water of relatively high salinity does not permit a firm conclusion about the origin of these metals, but there are some indications that local inputs may be important.

The ‘strength’ of the endogenous locomotor activity rhythm of four peracarid crustacean species, denned by the precision and persistence of the rhythm, was examined with particular reference to a ‘burrowing’ versus epifaunal supralittoral life-style. The ‘strength’ of the endogenous component of the activity rhythm was also illustrated using a modified periodogram analysis. In all species, the talitrid amphipods Talitrus saltator, Talorchestia deshayesi, Orchestra gammarella and the oniscoid isopod Ligia oceanica, the laboratory-monitored rhythm and the field emergence pattern displayed a nocturnal, circadian pattern with no clear evidence of any circa-tidal influence. The precision and particularly the persistence of the rhythm of the sand-shore burrowing species T. saltator and T. deshayesi are especially well developed, although a ‘strong’ endogenous component is present in the rhythm of all four species. The significance of the endogenous locomotor rhythms is considered with respect to the supralittoral ecology of the species.

Observations in the field, and in the laboratory, of littoral fishes of south-west England during the period 1978–80 have shown that the three blenniid species found with any frequency on the shore constitute an important link in food chains. The occurrence, age, habitat and diet of Blennius (Lipophrys) pholis L., Coryphoblennius galerita L., and Parablennius gattorugine Brunnich have been considered; B. pholis was by far the most common of the three, with very few P. gattorugine being found intertidally. Of the latter, only age groups 0, 1 and 2 were represented in the littoral populations, whereas in the truly littoral species age groups 0–10 were found for B. pholis and 0–6 for C. galerita. Measurements of growth rates for the three species have been compared with growth rates of B. pholis and C. galerita at other sites, and a similar treatment has been afforded to dietary constituents. A discussion of the possible competition for food and refuge between the three species, and with other littoral teleosts, concludes that highly efficient partitioning of resources reduces competition to a minimum, with the exception of abundant food items which are (in any case) probably underexploited.

Cod and plaice eggs show a gradually increasing rate of ammonia excretion during development and in neither species was there a great change in individual output at hatching. The rates of ammonia excretion recorded for cod and plaice larvae were similar to those recorded for planktonic Crustacea of comparable size by Conover & Corner (1968).

Lumpsucker eggs and larvae have a basically low rate of ammonia excretion (consistent with their slow rate of development and low oxygen consumption), but much ammonia was released from the eggs in the first day or two after spawning. This ammonia was of non-metabolic origin, but was not accumulated from the ovarian fluid prior to spawning. Lumpfish eggs become very sticky when they are first exposed to sea water, but this stickiness is lost within 24 h. Stickiness stems from a viscous elastic slime; it is suggested that the non-metabolic output of ammonia is caused by changes in the composition of the slime as the eggs are bound together in a lattice.

Lacuna vincta appeared at Musquash Head, New Brunswick, in large numbers from June to August 1981 principally on lower midlittoral and infralittoral fringe Fucus edentatus. The population reached a mean maximum of 280/m2 in June; by mid September the animals had disappeared. The L. vincta grazed heavily and deposited egg masses on Fucus edentatus but little on other species. All fine and filamentous and encrusting algal species and rock were avoided for egg deposition. Egg mass abundance peaked with the population in June with a mean of 180/m2. Mean egg production in June was 83000/m2.

Both snail and egg mass distributions were correlated with the percentage cover of F. edentatus, reaching a maximum at 40–75 cm above mean low tide level.

The snails ranged in length from 2–7 mm, consisting of three cohorts from different larval settlements. Growth was rapid in July averaging 0·6 mm/month slowing later.

The food plant Fucus edentatus showed a heavy impact of the herbivore. Weight reductions attributable to grazing rose from 56 % in June to 79 % in August and grazed plants tended to thicken rather than elongate with growth. Grazing removed about 79 % of the net production of F. edentatus which averaged 61 g dry wt/m2/day. The impact of the L. vincta population on F. edentatus seems extraordinarily severe.

The red muscle of the thresher-shark myotome is internalized and supplied by a simple rete in connexion with lateral vessels. It is probable that the system enables the fish to be warm-bodied.

INTRODUCTION

Warm-bodied sharks were first described by Carey & Teal (1969); subsequent observations by Carey and his colleagues (Carey et al. 1971) and by Carey (1982) showed that five lamnid species were able to maintain body temperatures 5–10 °C above the ambient water. All of these possess more or less elaborate retia linking a red muscle mass lying internally in the myotomes with the systemic circulation. In cold-bodied sharks, the red muscle lies superficially, just under the skin, and retia are absent. A sixth lamnid species, the big-eye thresher shark (Alopias superciliosus) may be warm-bodied; it has a simple muscle retial system (Carey et al. 1971) which has not been described in detail. The chance capture of a common thresher shark (A. vulpinus) enabled this short description of the retial system in this species.

The salmon shark, Lamna ditropis Hubbs and Follett, is a streamlined, pelagic predator capable of rapid swimming locomotion, very similar to its close relative, the Atlantic porbeagle, Lamna nasus (Bonnaterre). The porbeagle is warm-bodied, maintaining deep body temperatures 7–11 °C above those of the surface water from which they are captured (Carey & Teal, 1969a). Presumably, Lamna ditropis is also warm-bodied. Opportunities to measure temperatures of salmon sharks occurred on 2, 4 and 5 September 1979, when one of us (D.R.) hooked and landed three salmon sharks while hand-trolling for salmon. The sharks were all caught near Cape Edgecumbe, about 60 km from Sitka, Alaska (57° 6´N, 135° 55´ W) at a depth of 12–40 m.