The intertidal distributions of the two varieties of Actinia equina L. defined by Stephenson (1935), var mesembryanthemum and vai.fragacea, have been studied on several shores of the English Channel. The reproductive physiology and iso-enzyme genetics of sympatric populations of the two taxa have been investigated in greater detail on one shore. The genetic results show that the two taxa are reproductively isolated and, overall, the evidence indicates that they are separate species.

An energy budget has been assembled for a population of the limpet Patella vulgata inhabiting the mid-tide level of a moderately sheltered shore in the Isle of Man. The average biomass during the two year study was 346 kJ m−2, and the energy budget in kJ m−2 year−1:

Herring (Clupea harengus L.) show a marked ‘startle’ response when subjected to sound stimuli from a vibrating source (Blaxter, Gray & Denton, 1981c). The response, which occurs at a consistent threshold, is elicited by the first cycle of a tone burst or noise, the threshold to one cycle being the same as for a burst of many cycles. Furthermore, if the onset of the tone burst is ‘ramped’ so that it takes several cycles for the full amplitude to be reached, the threshold is markedly raised. Under some conditions the fish move away from the source, showing that they can determine its direction even though the stimulus is confined to a single cycle. The relative roles of sound pressure and particle velocity in providing information about the amplitude and direction of the noise have not been firmly established. Present evidence suggests that pressure is important in triggering the response and probably in measuring the strength of the stimulus. A vector such as particle velocity provides the directional information used in the response. The response can be very fast with a latency of about 25 msec and a contraction time of about 20 msec (Blaxter, Denton & Gray, 1981 b). In these very fast reactions the Mauthner cells probably constitute the motor pathway (Diamond, 1971).

The distribution, abundance and seasonal occurrence of larvae of mackerel (Scomber scombrus L.) are described from routine Continuous Plankton Recorder (CPR) sampling around the British Isles over the period 1948–78, and from more intensive CPR sampling in the Celtic Sea in 1977. There were two main areas of larval concentration: in the North Sea and over and adjacent to the Celtic Plateau; subsidiary aggregations were observed to the northwest of Ireland and to the west of Norway. There were some similarities between the distribution of larvae around the British Isles and that of adult Calanus spp. In the North Sea there was a southerly shift of larval distribution over the period 1948–77; over a similar period the abundance of larvae increased to reach high numbers by the late 1950s and subsequently declined after the mid-6os. To the south-west of the British Isles numbers of larvae showed a long-term decline. The long-term trends of distribution and abundance are discussed in relation to concurrent biological and environmental change. The clearest relationship was found between the numbers of mackerel larvae in the North Sea and sea-surface temperature in the North Atlantic, which suggests a common causative agent for both sets of observations; also, there was a weak relationship with both spawning stock biomass and sea-surface temperature at the spawning areas. In the North Sea the seasonal occurrence of larvae was from May to August, the majority being taken in June and July; over the period 1948–77 the seasonal time of occurrence of highest numbers of larvae has remained relatively constant. In the Celtic Sea the seasonal occurrence of larvae was spread over a longer period, from March to August, with relatively high numbers from March to June; over the period 1950–78 the time of occurrence has been variable, possibly with a tendency towards later timing in more recent years.

The ciliated epithelial sensory cells of the tentacle papillae and of the concave epipodial sense organ (e.s.o.) surface of the trochids Margaretes helicinus, Gibbula cineraria, G. umbilicalis, Monodonta lineata, Diloma nigerrima and D. zealandica are primary sensory cells with intra-epithelial nuclei. The 5–7 cells of a single papilla bear many cilia. Each e.s.o. cell has one cilium surrounded by 8–9 specialized microvilli. Both kinds of sensory cell show structural similarities with known mechanoreceptors.

Juveniles of Patella spp. in Britain are shown to be easier to classify than adults, on shell morphology alone, because of a species-specific difference in number and arrangement of the post-larval mantle tentacles. The limpets can thus be clearly divided into three distinct spp.: P. vulgata Linn., 1758, P. aspera Roding, 1798, and P. depressa Pennant, 1777, which confirms recent evidence from gel-electrophoreric studies. As the limpet grows, this initial difference gives rise to many of the variables of shell shape and colour upon which adult identification is based. In the process, it can be influenced by environmental factors to the extent of producing confusing phenotypes such as those hitherto supposed to be hybrid or genetically transitional forms. The characters described suggest that, contrary to current opinion, P. aspera and P. depressa are related more closely to each other than to P. vulgata; they may also have some bearing on the species' success and distribution in the British Isles.

Callista chione (L.). is a fairly large, handsome bivalve of the family Veneridae. It is found around the coasts of Devon, Cornwall and Wales, though its distribution extends southwards to the Mediterranean. It is usually uncommon but has been found to occur at the eastern end of Whitsand Bay, near Plymouth at a density of about 1 per m2. Several specimens were taken in 1975 while testing a water lift system for the use of aqualung divers. Most of the shells were observed to bear a noticeable growth check in the form of a ridge several millimetres from the shell margin (Fig. 1). This ridge was not found in the older specimens in the laboratory's museum collection. To try to find out the cause of this growth check a tagging experiment was undertaken in 1976, although it was not possible to measure and mark out large numbers; recaptures in the following two years have been sufficient to provide some evidence for the average growth increment of different sizes of shell.

There are three species of chthamalids in Europe. Two of them, Chthamalus stellatus and Chthamalus montagui, overlap extensively in geographic range: they occur together along the whole Atlantic coasts of Britain, Ireland, France, Spain and N. Africa, and both also occur in the Mediterranean Sea. They have almost identical north-eastern limits to their distribution in the English Channel and N. Scotland, but C. stellatus may extend farther south along the W. African coast. These two species also show overlap in their vertical distribution, though C. montagui is usually commoner in the upper barnacle zone while C. stellatus may be dominant lower down. The species are separated by habitat, C. stellatus favouring wave-beaten open coast sites, C. montagui more embayed situations, but there is still extensive overlap. The third European species of chthamalid, Euraphia depressa, has a more restricted vertical distribution and is almost entirely confined to the Mediterranean Sea, where it favours high-intertidal levels in wave-beaten places, and also cryptic habitats.

The rate of excretion of ammonia by Nassarius decreases progressively during starvation. Both Nassarius and Buccinum exhibit a transient peak of ammonia excretion some 16–48 h after a meal. In Nassarius the length of the delay between feeding and maximum ammonia excretion depends on the duration of prior starvation.

Closed circuit underwater television observations showed that, in summer, large numbers of Carcinus maenas performed daytime tidal migrations up and down a small mudflat in the Menai Strait, North Wales. At the observation point, 25 m above mean low water mark of spring tides, numbers of crabs moving upshore on flood tides averaged 84 m—1 of tideline, ranging from 48 to 126 m—1. Most crabs were of 20–50 mm carapace width (1 and 11 groups); none smaller than 15 mm was seen. Peak movements occurred in at least 0.5 m depth of water. Over the high tide period, most crabs were dispersed over the upper half of the mudflat where crab population densities of 1·8–2·5 m—2 were indicated by diving observations.

In attributing variations in growth and metabolism within a population to environmental fluctuations, and in interpreting the biological response to environmental fluctuations, it is important to recognize the variations that are intrinsic to the population or species. Consequently, it is common practice in studies on the growth and metabolism of calanoid copepods to separate instars and, in the case of adults, males and females when analysing measurements. Although studies on calanoids, in particular species of Calanus and Euchaeta, have demonstrated the existence of pronounced sexual differences in parameters such as dry weight, biochemical composition and respiration rate (e.g. Comita, Marshall & Orr, 1966; Marshall, 1973; Bamstedt, 1975, 1979; Gatten et al. 1979, 1980), the possibility that similar differences might occur in pre-adult instars has not been examined, this despite the fact that in many species in this group it is possible to distinguish the sex of copepodites IV and V, the two instars preceding the adult.

When exposed to water of low salinity specimens of Mytilus edulis L. keep their shell valves tightly closed; they do not gape periodically to test the external medium. Exchange of salts and water between the mantle cavity and the environment is thus minimized. Rising salinities are registered by diffusion of salts to the tentaculate portion of the inhalent siphon and not to any other portion of the mantle edge or to any more deeply located structures.

From observations in the aquarium and by a morphological study of the feeding tentacles it is concluded that Leptopentacta elongata is not, as is commonly supposed, a mucus suspension feeder, but feeds on deposited material by mechanical entrapment with the aid of sticky papillae on the tentacle buds.

In shallow hypoxic sea water female shore crabs (Carcinus maenas (L.)) incubating eggs on their abdominal pleopods reverse the direction of normal ventilation, taking air in at the normally exhalant opening and bubbling it out via apertures at the base of the posteriormost pair of walking legs and hence over the developing egg mass. The ambient oxygen tension at which the behaviour is elicited and the percentage of total time it is performed are both dependent upon acclimation temperature. The oxygen tension at which the behaviour is first observed coincided at different acclimation temperatures with the critical oxygen tension below which oxygen consumption of the developing eggs became dependent on further reduction in . The bubbling of air during the emersion response is sufficient to raise the oxygen tension of the water surrounding the eggs and is thus an attempt by the parent animal to maintain the oxygen uptake of the developing young. If left in a standing body of hypoxic sea water release of larvae is deferred until well-aerated conditions next prevail. Thus if the berried female is trapped in a rock pool the encroaching tide may act as a releasing stimulus which is of adaptive significance to the dispersal and survival of the larvae. When female crabs submerged in warm water (25 °C) bubbled cool air past the egg mass this had no significant cooling effect. The thermal tolerance of the developing eggs was low, rate of oxygen uptake being limited by temperature rises above 25 °C.

In an experimental study the cyclopoid copepod Corycaeus anglicus Lubbock was found to ingest Artemia nauplii at much higher rates (up to 15 times) in the light than in the dark. Maximal ingestion rates observed in the light represent daily rations of 70% and 66% of the body carbon for males and females respectively. From experimental observations together with studies of the ultrastructure of the photoreceptors it is suggested that Corycaeus can locate prey visually. This is in contrast to the majority of other copepods which use chemoreceptors and mechanoreceptors.

Symbiotic luminous bacteria have been described in, and cultured from, a number of species offish and cephalopod. Indeed only in these two groups are extracellular luminous bacteria believed to be utilized as a source of light (see Buchner (1965) and Herring (1978) for references). Despite several earlier investigations of such symbioses in cephalopods the bacteria in these animals have not been adequately identified, nor has the extent of their role been clarified. The ultrastructural relationships between bacteria and the tissues of the squid accessory nidamental gland have been investigated in the non-luminous species Loligo pealei (Lesueur) (Bloodgood, 1977) and Sepia officinalis L. (Van den Branden et al. 1979) but no comparative work on luminous species has been undertaken apart from that on Heteroteuthis dispar (Rüppell), whose photophore does not contain typical luminous bacteria (Dilly & Herring, 1978; cf. Leisman, Cohn & Nealson, 1980). The order Sepioidea contains five families, among which are the two families Sepiolidae and Spirulidae. Though the presence of luminous bacteria is known in some sepiolids (as well as in certain loliginids (order Teuthoidea)) some doubt remains about the source of light in the photophore of Spirula spirula Hoyle. The steady luminescence of this species has prompted speculation that bacteria may be involved (Harvey, 1952). In this paper we compare the anatomy and ultrastructure of the photophores of both Sepiola and Spirula in order to clarify some of these problems.

Whole body cooling of dogfish initially anaesthetized with MS 222 produced total immobility and permitted prolonged surgical procedures. Additional anaesthesia was not required, and on rewarming recovery was rapid.

Electromyographic recordings of jaw-closing and fin-elevating reflexes of the dogfish during body cooling indicated that processes within the central nervous system were being blocked and that the effect was most pronounced on polysynaptic reflexes.

Laboratory observations on the formation of concentric growth ridges on the shell of small Pecten maximus revealed that their rate of production was related to the size of the shell and to the growth increment in a given period. These factors are related, naturally, and the larger the shell, the greater is the growth increment and the number of ridges produced in a given time. Also, in shells of a similar size the higher the growth rate, the larger is the width of each ridge and the greater is the number of ridges produced. Faster growth is achieved therefore by increasing the width and number of ridges. The rate of ridge production at 10 °C was less than half that at 14·5 °C in conditions which were otherwise identical.

Previous work has indicated that, although in possession of numerous supposedly osmoregulatory structures, Branchiostoma lanceolatum from the English Channel is unable to regulate its body weight in diluted sea water. In vitro measurements of the rate of flagella activity in those organs similarly indicates no increase under hypo-osmotic stress. There is however quite a sharp threshold around 18‰, below which flagella activity ceases quite abruptly. A similar situation obtains with the gill cilia although the animal can remain alive at these salinities for a period of several weeks.

Stromateoids are fishes of the open ocean commonly found in association with gelatinous zooplankton (Mansueti, 1963; Haedrich, 1957). One genus, Tetragonurus, has been found inside the branchial chambers of salps (Emery, 1882; LoBianco, 1909) and cloacal chambers of pyrosomes (LoBianco, 1909; Fitch, 1949, 1951).