Crisp & Meadows (1962, 1963) have shown that aqueous extracts of whole barnacles, when applied to an inert test surface renders the surface attractive to barnacle cyprids thus simulating the gregarious response displayed at settlement. The factor responsible for promoting the settlement of cyprids of Balanus balanoides has been shown to be nondialysable, resistant to boiling in aqueous solution, and can be fractionated by precipitation with ammonium sulphate (Crisp & Meadows, 1962, 1963; Gabbott & Larman, 1971). In their 1962 paper, Crisp & Meadows showed that the settlement factor was present in untreated extracts of all the arthropod groups they examined (including Carcinus maenas) and in extracts of two species of sponges and the fish Blennius pholis. Extracts of other animals and plants were not active. In particular, untreated extracts of the bivalves Mytilus edulis and Ostrea edulis were inactive when assayed against cyprids of B. balanoides. Recently one of us has shown that boiled extracts, partially purified by precipitation with ammonium sulphate, of whole barnacles (B. balanoides, Elminius modestus and B. hameri), crab carapace (Carcinus maenas), whole heads of the blenny (Blennius pholis) and of the body tissues (excluding the shell) of O. edulis and M. edulis, all contain a characteristic group of acidic proteins, or protein-carbohydrate complexes, with iso-electric points in the range pH 4.0–6.0 (Larman, 1975). This finding has prompted us to re-examine the specificity of the settlement response in barnacles.

Elasmobranch fishes cannot at present be aged by scale or otolith readings as can certain teleosts. Consequently comparatively little is known about their age or rate of growth, particularly in the case of larger sharks. Alternative methods of age determination within this group have utilized tagging data (Bonham et al., 1949; Holden, 1972); size frequencies (Olsen, 1954; Aasen, 1966); the spine of Squalus sp. (Kaganovskaia, 1933; Holden & Meadows, 1962); tooth-replacement rates (Moss, 1967, 1972) and vertebral rings. These rings on the vertebral centra, resulting from variations in calcification, have also been used in the age determination of teleosts. In the scombroids there is often considerable variation in results even between authors working on the same species, mainly due to difficulty in interpreting the rings and deciding whether they are true year marks (Aikawa & Katô, 1938; Partlo, 1955; Otsu & Uchida, 1959; Hui-chong, Nose & Hiyama, 1965).

Assimilation efficiencies reported for bivalves vary, but different experimental conditions, in particular the concentration of the suspension at which the animals are fed, may affect the values found. Widdows & Bayne (1971) determined the assimilation efficiency for Mytilus edulis when fed Tetraselmis and they found that efficiencies decreased with increasing concentration of cells. Allen (1962) fed radioactively labelled Phaeodactylum to Mya arenaria and Venus striatula and suggested that the amount of P recovered in the faeces was proportional to the amount of algae ingested rather than to concentration of suspension directly. However, Winter (1969) concluded that for Arctica islandica and Modiolus modiolus there was no relation between assimilation efficiency and concentration of algae.

When the free-swimming larva of the polychaete tubeworm Spirorbis spirorbis settles permanently on a suitable substratum, it forms a thin, mucous, anchoring tube, which covers only the posterior half of the body. Within 3 h the worm has built a comparatively thick, calcareous tube onto the anterior end of the initial, mucous tube, which later becomes a compressed and folded remnant (Nott, 1973). The volume of calcareous material forming the tube cannot be stored within the body of the larva before settlement and must, therefore, be taken up rapidly from sea water or ingested material.

The importance of the blood in crustacean metabolism was first raised by Johnston, Davies & Elder in 1971. Until then the conventional view had been that the crab hepatopancreas had a role similar to that of the vertebrate liver (Vonk, 1960), the blood presumably acting as a carrier of soluble sugars. It has recently been shown, however, that blood tissue holds almost four times the amount of polysaccharide than the hepatopancreas and that glucose is actively incorporated into glycogen in the blood (Johnston & Davies, 1972). Polysaccharides were located in deposits in the haematocytes (Johnston, Elder & Davies, 1973). Many previous studies have shown that the main plasma sugar, glucose, varies widely in concentration and appears very sensitive to the animals physio-logical state (see Hohnke & Scheer, 1970). It would seem, therefore, that glucose metabolism in crabs may be readily modified and that by looking at the effect of a physiological stress (starvation and feeding) on the blood/hepatopancreas system one might get some information on the dynamic relationship between these two organs. Previous work (P. L. Lutz, unpublished) had shown that in Carcinus maenas plasma glucose could fall to negligible values on prolonged starvation.

Dense aggregations of echinoderms on the sea bed have been described from various parts of the world. Reese (1966) considered that such an aggregation ‘is a response to one or more essential environmental factors such as food or substratum, and does not reflect social behaviour per se’ Observations by Warner (1969, 1971) and by Brun (1969) suggested that, in aggregations of the brittle-star Ophiothrix fragilis, individuals may respond to conspecifics rather than solely to food or the substratum. On an apparently uniform substratum, some areas are covered with a dense bed of brittle-stars while other adjacent areas are devoid of brittle-stars. Warner (1971) pointed out that the aggregations are advantageous to the species so it seems possible that the animals might aggregate actively rather than coming to a suitable feeding area by chance. The aims in this study were to investigate the responses shown by Ophiothrix fragilis to its physical surroundings, to some of the other organisms living near it and, especially, to conspecifics. The animals studied are in dense aggregations off Berry Head in Southern England and all observations were made underwater in the natural habitat.

The echinoderm skeleton is interesting because its material is so different from that of other invertebrates. It is full of interconnecting cavities, and each piece of skeleton seems to be made of a single crystal of rather impure calcite (Nichols & Currey, 1968). An obvious question for a biologist is whether echinoderm skeleton is in some way better mechanically than other, more conventional, skeletal materials.

The known range of the northern rockling, Ciliata septentrionalis, extends from Iceland and northern Norway in the north to Plymouth in the south (Wheeler, 1965). This species has probably been confused with the five-bearded rockling, C. mustela (L.), in the past (Wheeler, 1969) and this together with the small size of the fish, enabling it to escape through the mesh of most trawls, may explain the paucity of records and knowledge of the species. Brook, (1885, 1888) described the egg and larval development of C. mustela but the egg and larva of C. septentrionalis have not been described. It is probable that the abundance of both these species can only be estimated by a combination of fecundity studies and egg and larval counts.

Although freshwater teleost cell and tissue culture is an established field, the in vitro maintenance and growth of marine or estuarine fish tissues and cells is less well reported (Wolf & Quimby, 1969). Small demersal gobiid teleosts of the genus Pomatoschistus Gill, 1864 are widely distributed and very abundant around the coast of Britain and play an extremely important role in estuarine and coastal ecosystems (Hartley, 1940; Miller, 1963, Ph.D. Thesis, University of Liverpool; Green, 1968). Excluding the in vitro maintenance of whole organs (e.g. Bonnin, 1971a, b and Doneen & Bern, 1974) the culture of cells or tissues from gobiids has not been reported.

The classification of the Rissoidae has been, and continues to be, based largely upon shell characters. In a group of small animals of variable form this has resulted in a state of considerable taxonomic confusion. Ponder (1965, 1967, 1968), in his works on the New Zealand Rissoidae, attempted to clarify, what he termed, the existing ‘pigeon-hole classification’ in the light of more detailed anatomical investigation. He observed (Ponder, 1967) that ‘many wrong assumptions can be drawn from the study of the shell alone’. In an earlier work Johansson (1939) had also tried to relate the taxonomy of the Rissoidae to anatomical features.

As recent studies have shown that in Crustacea the haemolymph plays an important role in carbohydrate metabolism (Johnston & Davies, 1972, Williams & Lutz, 1975) it is clear that a proper understanding of this phenomenon depends on an accurate knowledge of the variety of cell types found. However, an examination of the literature revealed a wide divergence of opinion in the recognition of various kinds, their relationships and their composition, with, for example, the same authors reaching quite different conclusions from similar evidence (Johnston, Davies & Elder, 1971, Johnson, Elder & Davies, 1973) (Table 1). This suggested that the subject required further examination. As both the type and number of cells may vary according to the condition of the animal (Sniesko & Taylor, 1947), it was decided to look at the blood of fed and starved specimens.

Basket-stars are suspension-feeders and suspension-feeding by other brittle-stars was suspected long ago on circumstantial grounds, but it is only in the last twenty years that it has been actually demonstrated, and detailed descriptions of suspension-feeding behaviour are still available for only a handful of species. Blegvad (1914) pointed out that Ophiothrix fragilis (Abildgaard) and other species lead sedentary lives and feed largely on detritus on, or near, the sea-floor. Wintzell (1918) explicitly suggested tha and Ophiopholis aculeata (L.) are suspension-feeders, primarily on the grounds that they are commonly found in current-swept localities where plankton is rich, in association with known suspension-feeders such as Modiolus, Lima and Alcyonium. The same suggestion was made by Vevers (1952) who noted the occurrence of dense aggregations of O. fragilis in offshore, current-washed areas near Plymouth, and who later observed suspension-feeding behaviour in that species and in Ophiocomina nigra (Abildgaard) (Vevers, 1956). This was only the second time that suspension-feeding had been documented for any (ophiurid) brittle-star, but now it has been described in about a dozen species and suspected in others, mostly members of the Amphiuridae, Ophiactidae, Ophiothricidae and Ophiocomidae (MacGinitie, 1949; Kuznetsov & Sokolova, 1961; Moore, 1962; Magnus, 1964; Buchanan, 1964; Fontaine, 1965; Fricke, 1970; Pentreath, 1970).

The muscles of the paired fins of rays have long been known to possess large sensory endings of a special type, first described in Torpedo by Poloumordwinoff (1898) and Cavalie (1902), and subsequently re-examined by Barets (1956). They consist of many parallel beaded nerve fibres, derived from a large myelinated parent axon, lying between the muscle fibres of the fins. That they respond to stretch (as was inferred from their structure and position) was shown by Fessard & Sand (1937). Since these are the only sensory endings known in any fish which are stretch receptors lying amongst muscle fibres (neuromuscular spindles are absent from fishes), more information about their structure and relationships with the muscle fibres of the fins is desirable. In this note, we describe the ultra-structure of this simple type of stretch receptor, and the type of muscle fibre with which it is associated.

In previous papers we have shown that high temperature and low food levels result in a decline in the body condition of mussels, Mytilus edulis, which have been kept in the laboratory (Bayne & Thompson, 1970; Gabbott & Bayne, 1973). In spite of the loss of body reserves, M. edulis is able to continue gonad development at an increased rate, when the temperature is above ambient (Gabbott & Bayne, 1973; Bayne, 1975). Although gametogenesis appears to be normal under these conditions, there is evidence that stress in the adult affects subsequent larval development in M. edulis (Bayne, 1972) and in the oyster, Ostrea edulis (Helm, Holland & Stephenson, 1973). In mussels, stress resulted in an increase in abnormal embryonic development during cleavage, gastrulation and development to the first shelled larval stage (Bayne, 1972). In oysters the viability of the larvae, assessed in terms of growth rate and percentage yield of spat, was less in larvae from adults kept at low ration than in larvae from adults kept at high ration. Irrespective of the feeding regime, the viability of the larvae fell as the length of the conditioning period increased, and this was related to a decline in the body condition of the adult oysters. The growth of the larvae in the 96 h period following liberation was significantly correlated with the lipid level in the newly released larvae (Helm, Holland & Stephenson, 1973).

Terebella lapidaria L. is a small terebellid common in crevices in the mid-littoral zone of rocky shores in the Plymouth area. The coelom contains abundant coelomocytes charged with haemoglobin in sufficient quantity to give the worm a brick-red colour. T. lapidaria also has a discrete vascular system with haemoglobin dissolved in the plasma. When covered by the tide the worm irrigates its burrow intermittently. When revealed by the tide it cannot do so, and is then left in a thin film of water or in moist air for 3–4 h. We thought it was of some interest therefore to determine the oxygen equilibrium characteristics of these pigments.

Periodic structures indicating discontinuous growth of shell wall plates have been observed in thin sections of shell and on the outer surface of shell plates of many species of operculate (Bourget, 1975). When sectioned and etched the shell plates appear to be composed of successive thin layers of shell material, each layer consisting of a few rows of fine crystals. Where two layers are adjoined, a dark line, marking the junction of two incremental zones, is clearly visible. The thin layers of shell have been termed growth bands whereas the junction of adjoining layers will be referred to as the growth line.

The organization, cellular composition and function of the digestive diverticula has been described for a large number of molluscs (Nakazima, 1956; Owen, 1966; Purchon, 1968). Changes in the digestive cells which are associated with intracellular digestion have also been widely recognized (Graham, 1938; Carriker, 1946; J. E. Morton, 1955, 1956, 1959; Owen, 1955, 1966, 1970, 1972; Sumner, 1965, 1966a, b, 1969; Morse, 1968; McQuiston, 1969; Walker, 1970; Merdsey & Farley, 1973). In general the digestive cells show three cyclic phases, (1) absorption, (2) digestion, (3) fragmentation and excretion, and these phases, with only minor modifications, are typical of most molluscs (Owen, 1966). In many groups, especially gastropods, the changes in the digestive cells within the tubules of the digestive diverticula often appear to be synchronized and consequently the tubules have a uniform appearance throughout the diverticula. In the Bivalvia, however, this type of synchrony has not generally been recognized. Since bivalves have been considered to feed more or less continuously (Purchon, 1971; Winter, 1973) it is not surprising that a homogenous appearance was only exceptionally observed, e.g. J. E. Morton (1956), J. E. Morton, Boney & Corner (1957).

While working on taxonomic problems in the family Dotoidae and comparing the Mediterranean and Atlantic species (Schmekel & Kress, in the Press), it became apparent that very little embryological information was available for this group, other than that published by Alder & Hancock (1845–55), Pelseneer (1911), Miller (1958, Ph.D. Thesis, University of Liverpool) and Thompson (1967).

In the course of studies on the changes in egg-capsule volume in different nudibranch species (Kress, 1971, 1972) a fresh attempt has been made to obtain some comparative data on egg and capsule sizes and on the course and rate of embryonic development in the three species of Doto most commonly found in the Plymouth area, namely D. coronata (Gmelin, 1791), D. pinnatifida (Montagu, 1804) and D. fragilis (Forbes, 1838).

A survey by Yonge (1962) of the byssal apparatus in the Bivalvia indicates that the formation of byssus is a larval characteristic which may or may not be retained in the adult. Some species such as the mussel, Mytilus edulis, retain the byssal attachment but have the ability to break the byssus and move over a limited area. Others, such as the scallop, Pecten maximus, lose the byssus entirely, become unattached and move by swimming. Yet others, such as the oyster, Ostrea edulis, relinquish all mobility at metamorphosis by cementing the shell to the substratum, and after metamorphosis lose all trace of the foot. Ostrea, Mytilus and Pecten therefore encompass a wide variety of life styles in the adult and are chosen as examples for detailed comparison of the byssus forming glands and other foot glands in the pediveligers.

Like most heavy metals, cadmium is only found in minute amounts in natural sea water. Krauskopf (1956) stated that cadmium concentration of normal sea water ranges from 0.032 to 0.075 PPb (μg/l−1) while Goldberg (1965) gave a somewhat higher value of 0.11 ppb. Cadmium concentrations determined by Preston (1973) for the North-East Atlantic Ocean range from <0.01 to 0.41 ppb, and similar values have been found by Windom & Smith (1972) in the West- and Chester & Stoner (1974) in the South Atlantic Ocean (0.04–0.17 ppb).