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.

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).

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.

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.

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.

It is known from earlier work (Blaxter & Jones, 1967; Blaxter, 1968a; Blaxter & Staines, 1970) that the larvae of many species of teleost have a pure-cone retina. The rods only appear well after hatching and often as late as metamorphosis. This means that much of the larval life may be spent without fully developed eyes. The rods are difficult to resolve under the light microscope using paraffin sections (about 5 µm) and it is therefore easier to compare the number of cones with the prominent visual cell nuclei in the outer layer (ONL) in such preparations. The ratio has been found to be 1:1 in the early stages and changes as the rods develop, reaching ratios of 1:15 or more in adult fish. Thus, for every cone there may be 14 or more rods.

The Marine Biological Association (1957) lists the poor cod Trisopterus minutus minutus (L.) (=Gadus minutus) as being parasitized by two monogenean gill parasites Diclidophora luscae and D. denticulata but at various times over the past 25 years we have, between us, examined the gills of upwards of 1000 specimens of T. m. minutus without ever having found a monogenean parasite. We concluded that the 1957 records were probably due to a misidentification of the hosts. However, in January 1979 one of us (J. E. G.) found several specimens of a monogenean very closely resembling D. luscae (Beneden & Hesse) on the gills of poor cod. D. luscae is normally found at Plymouth (Llewellyn, 1956) on only the pouting Trisopterus luscus (L.), a fish which from time to time is caught in the same trawl as T. m. minutus, e.g. in a total of 46 standard hauls between July 1976 and June 1978 (information supplied by Mr A. D. Mattacola), on 11 occasions (23%)T. luscus and T. m. minutus were caught together. On eight of these 11 occasions the lesser abundant of the two fish species constituted 10% or more of the combined total, and on three occasions the lesser abundant fish made up at least 40% of the combined total. Thus there is evidence that T. m. minutus and T. luscus from time to time occupy the same or neighbouring habitats (a standard haul may be over a distance of up to 8 km) and so presumably there has been opportunity for parasitic invasion from one species to the other to take place. That this has not in fact happened we have regarded as an example of the very strict species-specificity to their hosts manifested by most monogeneans and especially by diclidophorans on gadoids (Llewellyn & Tully, 1969). It was decided therefore to investigate how the sudden appearance in 1979 of a monogenean parasite on a previously uninfected population of poor cod may have come about.

While collecting acanthocotylid monogeneans for various investigations (Kearn, 1967; Lyons, 1972; Macdonald, 1974) Mr J. E. Green of the Laboratory of the M.B.A. at Plymouth has very occasionally found specimens of what each of these authors has suspected may be a new species. In July 1978 nine more living worms were collected, the material was indeed found to require the erection of a new species and we propose to call the parasite Acanthocotyle greeni.

It is well established that crustaceans can overcome infection and clear foreign material introduced into the circulation (Cornick & Stewart, 1968; Tyson & Jenkin, 1973; Stewart & Zwicker, 1974). In the absence of vertebrate-type specific acquired immunity, the non-specific activity mediated by the circulating blood cells appears to be of considerable importance in resistance to disease (Sindermann, 1971). Among the cellular defence mechanisms of the Crustacea, phagocytosis has received most attention and there is considerable evidence from in vitro studies that this process plays an important part in the removal of foreign particles from the blood (McKay & Jenkin, 1970a; Paterson & Stewart, 1974; Tyson & Jenkin, 1974; Paterson, Stewart & Zwicker, 1976; Smith & Ratcliffe, 1978). Such studies, however, may not always reflect the true in vivo condition, and there is a great need for correlated in vitro and in vivo investigations.

Diel variations in the emergence of the burrowing prawn Nephrops norvegicus (L.) have been investigated by direct field observations (Chapman & Rice, 1971; Chapman, Johnstone & Rice, 1975; Chapman & Howard, 1979; Atkinson & Naylor, 1976), and indirectly by sequential trawling during 24 h periods (Höglund & Dybern, 1965; Simpson, 1965; Hillis, 1971; Farmer, 1974; Atkinson & Naylor, 1976; Oakley, 1979). Peak emergence appears to be related to temporal and depth-dependent variations in daylight penetration, since Nephrops are apparently nocturnal in shallow waters, crepuscular as the depth increases, and diurnal at the greatest depths of their occurrence. This lends support to the suggestion that emergence occurs at an optimum light intensity (Hillis, 1971; Chapman, Priestley & Robertson, 1972; Chapman, et al., 1975; Chapman & Howard, 1979). However, additional factors influencing emergence of Nephrops from their burrows have also to be taken in account, since laboratory studies of locomotor activity in Nephrops have consistently revealed nocturnal activity patterns in light-dark (LD) regimes, with light inhibiting locomotor activity even at extremely low irradiance levels (Arechiga & Atkinson, 1975; Atkinson & Naylor, 1973, 1976; Naylor & Atkinson, 1976). Moreover, Hammond & Naylor (1977 a) have presented qualitative evidence that the nocturnal locomotor activity peak appears to be synchronized by falling light intensity at dusk. The differences between these experimental results and emergence patterns deduced from trawl catches and underwater observations of Nephrops have not been fully resolved by studies of the role of light intensity and of gradual light transitions (Arechiga & Atkinson, 1975; Hammond & Naylor, 1977 a, b). Thus the behavioural responses of Nephrops both in the field and in the laboratory need to be assessed in relation to more accurately quantified light changes. Also, despite earlier evaluation of the problem (Atkinson & Naylor, 1976; Hammond & Naylor, 1977a) it is necessary to reconsider the possibility that the patterns of locomotor activity recorded in the laboratory are influenced by experimental conditions, as has been demonstrated for minnows (Jones, 1956), and flatfish (Verheijen & de Groot, 1967).

According to its mouthparts Calanoides carinatus is a herbivorous filter-feeder (Mensah, 1974a; Schnack, 1978) that is often associated with phytoplankton blooms. The species has been reported from the three oceans and the Mediterranean (Vervoort, 1946). Interest in this copepod is increasing due to its apparent importance as a dominant link between phytoplankton and fish in upwelling areas. Its presence in surface waters is regarded as an indication for upwelled water (Bainbridge, 1972; Binet, 1973). Population dynamics and life-cycle have been studied best on the West African shelf (Mensah, 1974b; Binet & Suisse St Claire, 1975; Petit & Courties, 1976; Binet, 1977). Courties (1978) has recently given a comprehensive review of the literature on C. carinatus. In the above-mentioned studies, generation time usually is estimated by measuring successive peaks of larval stages and adults as well as using sex ratio and length distribution. In spite of its importance, C. carinatus has not yet been successfully reared in the labora-tory. Tomasini & Petit (1977) determined experimentally the developmental time of eggs and some copepodite stages, but could not obtain all stages. Schnack (1978) studied the feeding behaviour in feeding and assimilation experiments using various species of algae on board ship.

Hermit crabs, Pagurus bernhardus L., are common inhabitants of the littoral zone where they may be found in pools and puddles on the lower and middle portions of rocky shores. Only small specimens are normally found between the tidemarks but large crabs are found sublittorally as deep as 450 m. Unlike many of the animals found at a similar level on the shore, such as mussels, barnacles and winkles, Pagurus does not penetrate estuaries to any great extent. However, the smaller animals found in the littoral zone are likely to encounter reduced salinity levels caused by rainfall and terrestrial runoff.

The functions and structure of the pericardial glands (Keber's organ) of bivalves were reviewed by White (1942). The cells of this gland have been considered to have an excretory role and Grobben (1887) suggested that the cells of the pericardial gland could be compared with the chloragogen cells of annelids.

This is the first detailed analysis of cephalopod beaks from the stomach of a northern bottlenosed whale, Hyperoodon ampullatus (Forster, 1770). The digestive action of many predators barely affects the chitinous beaks of cephalopods and some cetaceans accumulate the beaks in considerable numbers in their stomachs. The present beaks are clean and unbroken.

Identification of cephalopod beaks from stomachs of predators such as sperm whales (see Clarke, 1977), seals (Clarke & Trillmich, 1980) and albatrosses (Clarke, Croxall & Prince, 1980) throws considerable light on the biology and relative ecological importance of the species of cephalopods concerned as well as providing useful information on the diet of the predators.

The inter-organ nutrient transport in echinoderms has presented an interesting but as yet unresolved problem for more than eighty years. During that time two systems have been proposed as candidates for the transporting medium or transport route, namely the coelomic fluid and the haemal system.

Echinoderms are not generally considered to experience significant dilution of the surrounding medium in their usual marine habitats and so it is to be expected that, due to the absence of any obvious excretory organ, the ionic composition of the body fluid would be similar to that of the ambient sea water. In general this has been confirmed by previous workers for many species of echinoderm. Binyon (1966) lists the results of workers who have determined osmotic pressure and/or ionic concentrations in the perivisceral and/or ambulacral fluids of many echinoderms. With reference to the perivisceral fluid in asteroids there is usually a small excess of potassium (9–16%) which is maintained in the more euryhaline species and in those acclimatized to reduced salinity. Generally, the chloride content is similar to, or a little higher than, that in the surrounding sea water. In echinoids there is little difference in the potassium content and chloride concentrations with respect to sea water though there may be a small increase in the former ion. In the holothurians, there is little regulation of potassium ions. Such concentrations which have been determined for the chloride ion in this group are found to be a little higher than in sea water. The sodium concentration in the perivisceral fluids of echinoderms tends to be similar to, or slightly lower than, that in the surrounding sea water. However in the ambulacral fluids of the water vascular system it has been shown that the potassium concentration is 20–90% higher in some species of asteroids and echinoids (Robertson, 1949; Binyon, 1962,1966). The fluids of the water vascular system of echinoderms, analysed to date, have concentrations of sodium ions lower than in the ambient sea water. From the available evidence, there appears to be little difference between environmental and ambulacral chloride concentrations.

Previous studies on the significance of dissolved organic compounds in the nutrition of the smaller species of the phylum Pogonophora (Little & Gupta, 1968, 1969; Southward & Southward, 1968, 1970) were handicapped by lack of information about the levels of free amino acids in the tissues. In this brief note we give preliminary results for four species, using a modification of the technique described by Clark (1964, 1968, 1973) to estimate the amino acids in extracts of the whole body.

One commonly held opinion about the metabolism of intertidal gastropods has recently been expressed by Newell (1970) who stated that in moist air these - as well as other intertidal - animals will respire air ‘whereas under conditions of desiccation closure of… the operculum… may result in anaerobic respiration occurring with the production of lactic acid’ (pp. 266–267). However, although anaerobiosis certainly does occur in intertidal gastropods (Patané, 1957; McMahon & Russell-Hunter, 1978) the conditions controlling this type of metabolism are far from clear. Moreover, recent studies (summarized by de Zwaan, 1977) have revealed a complex pattern of anaerobic metabolism in invertebrates in which the production of lactate is only one - and certainly not the most important - element.

In England the fisheries for both scallops (Pecten maximus) and queens (Chlamys opercularis) expanded rapidly in the 1970s. Considerable research has been undertaken to develop an effective method of surveying stocks of these species in order to assess the impact of this greatly increased fishing effort on commercial populations. Visual photographic surveys seemed likely to provide the best means of assessing populations (Pickett & Franklin, 1975) and this paper outlines the preliminary results obtained from such a system - a towed sledge carrying both television and still cameras, developed at the Plymouth Laboratory.

Actinia equina var. mesembryanthemum, the beadlet anemone (Stephenson, 1935), is a very common and widely distributed littoral anthozoan, whose sexual reproduction shows several interesting characteristics. Adult sea anemones of both sexes brood planulae and more advanced developmental stages within the gastrovascular cavity, although earlier embryonic stages are rarely found brooded in this way. Chia & Rostron (1970) suggest that embryos are expelled from the parent female anemone at an early stage and pass through a free-living phase before re-entering anemones of either sex for brooding. However, recent work (Cain, 1974) suggests that juvenile anemones are genetically related to the adult anemones in which they are brooded, and also the distribution of genetic material during sexual reproduction appears to be abnormal (Carter & Thorp, 1979). In an attempt to achieve a better understanding of the unusual sexual reproduction of this species, an ultrastructural investigation of gametogenesis was undertaken. This paper describes the fine structure of the spermatozoon within the testis.