The organization of the alimentary canal of fishes differs greatly between species of different dietary habit, but is not well understood. The vagus and sympathetic systems are very different in elasmobranchs and teleosts, but there has been little work on the corresponding physiology and pharmacology. The digestive system of elasmobranchs has unusual features connected with the fact that the absorbtive surface is provided by the spiral intestine (Fig. 1). This is a short fat tube whose surface is greatly increased by the presence of a coiled fold, the spiral valve. This arrangement provides a large area for absorbtion, neatly packed, but it leaves only a narrow lumen, so that no large particles can pass along the spiral intestine. Presumably it is in connexion with this condition that the stomach is divided into two parts. The cardiac division is a large sac into which the prey is received whole, its wall is very glandular and much breakdown of the food proceeds there (Hogben, 1967). The pyloric division is a narrower tube, leading from the hind end of the cardiac part to the pylorus.

The swimbladder of teleost fishes is a gas-filled sac which serves primarily to make the fish neutrally buoyant in sea water, but occasionally assumes other functions. The gas contained in the swimbladder is largely oxygen, at a pressure very close to the external hydrostatic pressure. The difference in gas partial pressure between the gaseous contents of the swimbladder and the blood and tissue fluids is large in fishes living at any considerable depth, for the hydrostatic pressure increases about 1 atm with each 10 m depth, while the partial pressures of gases in sea water and body fluids are relatively independent of depth and together give a pressure of only about 1 atm. The difference in partial pressure of oxygen alone across the wall of the swimbladder of a fish living at 3000 m depth is close to 300 atm.

Laboratory observations indicate that larvae of Pecten maximus (L.) pass through three phases of swimming behaviour before metamorphosis. Trochophores and early veligers generally swim upwards and, in shallow containers, tend to accumulate at the surface. Their swimming cilia beat without interruption so swimming is continuous. After 3 days of development, pauses in ciliary beating occur intermittently and the veliger becomes capable of withdrawing into its shell. It alternately swims up a vertically orientated spiral and sinks. This type of swimming behaviour is also displayed by the pediveliger, but this larva also periodically swims close to, or crawls on, the substratum. The tendency to accumulate at the surface becomes less pronounced as larvae grow older. By the pediveliger stage it is replaced by an increasing tendency to accumulate close to the substratum.

The effect of copper upon carbon fixation in coastal phytoplankton assemblages has been studied in relation to both the metal concentration in the water and the levels taken up by the plant cells. The phytoplankton populations were those present in water samples collected from Station L4 in the English Channel in the late autumn of 1979. The lowest copper concentrations causing detectable inhibition of photosynthesis lay in the range 1–25 μg/1, well below the levels which have been reported to be present in some sea areas around the British Isles; metal pollution may thus be influencing primary production in these contaminated regions.

Limpet populations of the genus Patella from the south-west coast of England were examined by means of gel electrophoresis in order to settle debate on the specific status of the three Patella forms. Populations varied morphologically along an east-west gradient, from three distinct forms in the west to continuous intergradation in the east, in accord with earlier studies. Patella collected were divided into three groups on the basis of a complex of external features described by earlier workers, corresponding to the morphologically defined taxa P. vulgata Linn., 1758, P. aspera Röding, 1798, and P. depressa Pennant, 1777. These groups were electrophoretically distinct in five of seven enzyme systems examined, with no hybrids or intermediates. Incomplete speciation and hybridization can be ruled out as possible causes of the observed morphological variation.

There are not sufficient data available to allow any general statements about the earlier stages of evolution of the autonomic nervous system and of its various transmitter mechanisms. In the previous paper (Young, 1980) it was shown that control of the stomach of elasmobranchs is largely by the inhibitory action of the sympathetic nerves, probably mediated by 5-HT. In teleostean fishes on the other hand control seems to be mainly by the cholinergic excitatory action of the vagus, especially in the more advanced (acanthopterygian) groups (Grove & Campbell, 1979a, b; Fänge & Grove, 1979).

In the family Alepocephalidae there are ca. 19 valid genera (Markle, personal communication). Whilst luminescence has never been observed, there are four genera, Xenodermichthys, Photostylus, Rouleina and Microphotolepis, which contain species bearing structures that have been interpreted anatomically as photophores (Herring & Morin, 1978). Among these four there is a remarkable diversity of photophore structure. The photophores of Xenodermichthys and Photostylus are similar in having well developed central cores (reddish violet in Xenodermichthys) and reflector layers, yet those of Xenodermichthys are sessile whilst those of Photostylus are borne on stalks (e.g. von Lendenfeld, 1887; Best & Bone, 1976). Not all species of Rouleina have light organs but where they are present they are sessile. Photophore structure of Rouleina has been examined only in R. maderensis Maul and was found there to be rather degenerate in adults (Markle, 1978). The light organs of Microphotolepis multipunctata Sazanov and Parin differ yet again in being scale covered, which contrasts with the naked photophores in the other three genera (Sazanov & Parin, 1977). The abundance and distribution of photophores in adults also varies with genus and species. Thus in Microphotolepis and Xenodermichthys they are extremely numerous and regularly arranged but in Photostylus they are few and less ordered (Günther, 1887; Beebe, 1933; Sazanov & Parin, 1977). In different species of Rouleina photophores may be relatively abundant and regularly arranged or few in number without such regular pattern (Maul, 1948; Uyeno & Kishida, 1977; Markle, 1978).

Data on the distribution of dinoflagellates in the surface waters around the British Isles in July 1977 were analysed by correspondence analysis. Four communities of dinoflagellates were recognized, and the occurrence of each was related to various environmental parameters. The vertical stability of the water column is considered to be the most important factor in determining the relative abundance of individual species.

There is some controversy about the strength of the stock of mackerel in the Celtic Sea and off the coasts of Cornwall and Ireland, and it is difficult to find out if the numbers of mackerel in this area have fluctuated in the past (Johnson, 1977; Lockwood & Johnson, 1976; Lockwood, 1978; Coombs, Pipe & Mitchell, 1977,1979, 1980). The earliest complete survey of the south-west spawning grounds was made in 1937–9 (Steven & Corbin, 1939; Corbin, 1947) and was principally designed to show the seasonal and geographical pattern, not provide a basis for stock evaluation. Nevertheless, this survey is the only information we have about the breeding of mackerel in the days before the war when fishing was performed with drift-nets and lines, a period when we can assume exploitation was very much less intense than today when trawls and purse-seines are used. Attempts to use the 1937–9 data for estimation of the pre-war stock have been regarded as giving unsatisfactory results (Walsh, 1976). The data from the 1937–9 surveys were defective because we did not know the influence of the depth of fishing of the nets in relation to the vertical distribution of the eggs, nor the efficiency and catching capacity of the nets for sampling eggs and post-larvae.

During a survey of teleost skeletal muscle (Greer Walker & Pull, 1975) it was found that the morphology of the red or slow muscle fibres of the anchovy (Engraulis encrasicolus L.) was markedly different from that of other species. In transverse section the fibres appear flattened as lamellae and are considerably larger in area than those of comparable species. This paper describes some aspects of their morphology, function and growth in comparison with other species.

Arsenic concentrations in estuarine sediments from England and Wales range over three orders of magnitude. The highest concentrations, up to 2500 μg/g, occur in the sediments of estuaries in south west England associated with past or present metalliferous mining activity. Strong correlations exist between arsenic and iron in 1 N-HC1 extracts of different estuarine sediments. The As/Fe ratio in those estuaries not contaminated with mine wastes is 11 × 10−4, increasing to 190 × 10—4 in metalliferous sediments.

The uptake, transport, storage and excretion of zinc has been studied in Mytilus edulis. Zinc accumulates in the soft tissues in proportion to its concentration in sea water whilst the concentration in the haemolymph is little above that in the environment. Uptake is via the gut, mantle and gills. The zinc is transported from the gills and gut (t½ ≈ 8 days) via the haemolymph, either as a high molecular weight complex or in the granular amoebocytes, to the kidney. Most of the body zinc is present in the granular amoebocytes (which are found in all the body tissues) or in the gut and kidney. The kidney forms the major storage organ for many trace metals, containing 30% of the body zinc and a concentration of about 1000 μg/g. Zinc is localized as insoluble granules in membranelimited vesicles occupying some 20% of the cell volume. Excretion of zinc is by defaecation, exocytosis of the kidney granules into the urine and diapedesis of the amoebocytes. A multicompartmental model for zinc metabolism which correlates the ultrastructural and kinetic data is proposed.

Opportunities for measurements on living Nautilus are rare, and such studies as there have been on its locomotion tend to treat it as primitive compared with modern cephalopod molluscs. But the few measurements we were able to make on a healthy captive Nautilus living for several months in the Monaco Aquarium reveal considerable sophistication in the control of swimming - particularly in the way the funnel operates - and that the system possesses neuromuscular properties that may be fundamental to cephalopods as a whole. The use of the shell for transmitting the pressure pulse and for the in- and out-movements of the body during jetting are, however, peculiar to this member of the group.

Mucus, leaving the pyloric duct in a continuous flow, is conveyed over the epithelium of the aboral part of the pyloric stomach. There nutrients are resorbed and concentrated into the haemal system, which is in close contact with this part of the stomach. It is supposed that this material consists of nutrients in complex form especially destined for the use of gonad development.

Growth rates in shell height on the shore and the number of eggs released in the laboratory during the spawning season were extremely variable among Littorina neritoides from a population on Anglesey, N. Wales. Much of this variability was attributed to the effects of unpredictable weather conditions on feeding activity. Thirtyper cent of the individually tagged snails in the population did not grow during 1976–8. Growth increments of the remaining snails were used to estimate the growth parameter, k, of the von Bertalanffy growth equation, and the asymptotic size, h∞, used in the equation was estimated to be 7·5 mm, corresponding to the largest individual found in the population. The von Bertalanffy equation was then used to construct a growth schedule for L. neritoides from post-settlement to the attainment of the asymptotic size. From this schedule, snails were expected to take at least 9 months to grow to a shell height of 2 mm and at least 5 years to grow to 7 mm. This growth schedule agrees closely with growth rates observed by Lysaght (1941) in a population at Plymouth, but predicts much lower growth rates than those estimated by Daguzan (1976) for a population in Brittany. Eggs were released from March to June in 1977 and from January to June in 1978. The extreme individual variability in egg production largely obscured the underlying relationship between fecundity and body size. The maximum observed fecundity was for a 71 mm snail which released a total of 3866 eggs during the 1978 spawning season. The average fecundity was 22 eggs per day during the 1978 spawning season, or about 300 eggs per season.

The small gadoid Trisopterus minutus (L.) is one of the most abundant demersal fishes on the Plymouth trawling grounds, though it is not retained in any number by the meshes of commercial trawls (Marine Biological Association, 1957). Correspondingly, the post-larval stages can be very numerous in the routine macroplankton collections at the Eddystone (Russell, 1973). However, in 1971 and 1972 T. minutus was accompanied by a few post-larvae of two other small gadoids, T. esmarki and Micromesistius poutassou (Russell, 1973,1976), and it was suggested that these might have drifted into the Plymouth region from spawning grounds farther to the west. A recent southerly shift in the main spawning region along the edge of the continental shelf was noted by Bainbridge & Cooper (1973), and Coombs (1975) has reported corresponding shifts in deep water species.

Aspects of the digestive cycle of Carcinus maenas have been studied by transmission and scanning electron microscopy, X-ray microanalysis and light microscopy. Movements of ingested material have been followed by feeding the crabs with Mytilus edulis (L.) labelled with colloidal particles of gold or thorium oxide.

Bivalve larvae constitute an important part of the plankton and there is a pressing need to be able to identify the various species.

The study of the development of the larval and post-larval hinge by scanning electron microscopy of 18 bivalve species shows the importance of this structure, which represents the principal character in identification of the young larval stages. This paper presents the principal distinguishing characters of the hinge (denticles, teeth and ligament) in eight families of bivalves.

Although cadmium concentrations of unpolluted sea water are low, ranging from 0.01 to 0.41 µg/1 (Goldberg, 1965; Preston, 1973; Chester & Stoner, 1974; Kremling & Petersen, 1977) concentrations in estuaries are from 10 to 100 times higher, as reported by Butterworth, Lester & Nickless (1972) for the Severn and Eustace (1974) for the Derwent estuaries. Unusually high cadmium concentrations of 50 µg/1 have been found by Chan, Cheung & Li (1974) in Hong Kong harbour water. The cadmium in the drinking water (225 µ/l) and the food (rice) of Japanese farmers is believed to have caused the ‘itai-itai’ disease (Kobayashi, 1971), a pathological syndrome characterized by kidney damage with bone disease.

Cephalopod statoliths are paired calcareous stones which lie in cavities, the statocysts, within the skull. They have a form which, though variable, shows promise as a source of criteria for taxonomic and evolutionary studies. As a preliminary to more detailed studies, Clarke (1978) published a description of the form of a generalized teuthoid statolith, coined nomenclature for the various parts and gave a very brief survey of variation of statoliths within the living Cephalopoda. This nomenclature was used in a detailed description of fossilized teuthoid statoliths by Clarke & Fitch (1979). Here, descriptions of the statoliths of the living species Berryteuthis magister (Berry, 1913), Gonatopsis borealis Sasaki, 1923, Gonatopsis (Boreoteuthis) makko Okutani & Nemoto, 1964 and Gonatus fabricii (Lichtenstein, 1818) are given and the fossil Berryteuthis species described in outline by Clarke & Fitch (1979) is compared with B. magister. A statistical analysis of measurements of the statoliths of these five species has been made and the results are presented. This forms the first part of a general description of teuthoid statoliths and similar studies on the Ommastrephidae and the Loliginidae are in preparation.