The bristle-bearing receptors on either side of the trunk in Oikopleura are connected to the caudal ganglion by the axons of central cells which form electrical synapses (gap junctions) at the bases of the receptor cells. The same axons also form similar synapses with epithelial cells adjacent to the receptors. Direct mechanical stimulation of the receptor processes evokes changes in the locomotor rhythm of the same kind as evoked by action potentials propagated in the epithelial cells. This remarkable arrangement is suggested to be a consequence of the reduced numbers of cells in larvaceans.

Using light microscope histology and scanning electron microscopy, the secretion, storage and discharge of copious quantities of mucus has been demonstrated in the algadwelling harpacticoid copepod Diarthrodes nobilis (Baird). The mucus is secreted by cells closely associated with large haemocoelomic reservoirs, located in the cephalothorax and urosome, which store the mucus prior to its discharge through large integumental vents (up to 38 μm in greatest dimension). A denned behavioural sequence is recognized whereby the animal utilizes discharged mucus to construct an enmeshing capsule. Late stage nauplii are also capable of capsule fabrication.

The mucus bag presumably, acts as a rich and rapidly degradable substrate to marine prokaryotes and is therefore rapidly colonized; suspended organic and inorganic materials are also trapped by the mucus. Observations on gut contents and browsing activity of capsule inhabitants indicate a direct trophic dependence of D. nobilis on the bacteria and organic agglutinations that adhere to the mucus. Utilization of such nutritive materials supports a ‘mucus-trap’ hypothesis recently proposed as a feeding strategy in meiobenthic nematodes.

Barnacle cypris larvae, the specialized settlement stage of the life-cycle, are classical examples of larvae showing gregarious settlement. Gregarious settlement is shown when the larva is induced to settle by established individuals of its own or of a closely related species, reflecting the ability of the larva to recognize its own type, usually by chemo-tactile detection of a particular settlement inducing factor (see Crisp (1974) for review). Sessile barnacles such as species of Balanus or Chthamalus are typically hermaphrodite and gregarious settlement is of selective advantage in promoting the possibility of cross-fertilization, in addition to allowing a settling larva to identify a habitat providing all the necessary conditions for barnacle growth and development.

The R, F and B cells of the hepatopancreas of Carcinus maenas are derived from undifferentiated (E) cells at the distal end of the tubules. Observations with the scanning electron microscope on freeze fractured tubules show that (a) most of the concentrically structured granules are confined to the R cells with few in F or B cells, (b) within individual R cells, granules are of similar size, and (c) the further R cells are situated from the distal end of the tubule, the greater is the mean diameter of the granules that they contain.

The presence in Calanus finmarchicus of the sex hormone oestradiol-17β has been confirmed by gas chromatography-mass spectrometry (GC-MS) using the trimethylsilyl and heptafluorobutyrate derivatives.

Levels of the sex hormone testosterone have been measured by radioimmunoassay in Calanus helgolandicus collected from Plymouth Sound, and in C. finmarchicus captured off the Norwegian coast. Concentrations in C. helgolandicus varied during the year from 150 to 626 fg/animal, accounting for 2.3 to 437 x 10-7% of the lipid content and 10.8 to 64.8 x 10-6%percnt; of the total sterol fraction. The mean level in Stage V C. finmarchicus, captured during spring, was 196 fg/animal.

Testosterone was identified in C. finmarchicus by GC-MS of the tert-butyldimethylsilyl derivative.

The distribution of 18 common epizoic species between clumps of Nemertesia antennina is examined with reference to their dispersal behaviour and, for selected epizoites, to the occurrence of other epizoic species. Dispersal of the tubicolous amphipods Ericthonius brasiliensis, Jassa falcata and Corophium sextoni and the caprellids Pseudoprotella phasma and Caprella linearis by a proportion of the adult animals, and by some animals after mating, was suggested. This behaviour may establish and perpetuate aggregations of these amphipods since brood-mates, and some of their descendants, remain on their natal hydroid clump. Five of the nine species considered that disperse as planktonic larvae have aggregated dispersions and for two of these species, Rissoa parva and Cingula semistriata, gregariousness of their larvae at settlement was considered an important influence on their distribution. Comparisons between the distributions of selected epizoic species suggest that in only a few cases, notably where branching bryozoans may give protection to potential prey species, is the distribution of one species influenced by the occurrence of another.

This paper describes a new asterinid starfish found first in southern Britain, but now also known from the Mediterranean and the Adriatic. Detailed comparison is made between the new species and the closely related Asterina gibbosa in terms of morphology, reproductive biology and life-history. The new species is adapted for life on the upper parts of rocks and on perennial algae in intertidal rock pools; it is small in size, matures early, lays large eggs, broods its young and has a short life span.

The glands which secrete the byssus in bivalve molluscs are located in the foot. Some glands discharge into a duct at the proximal end of the foot whilst others discharge into a ventral groove which runs forward from the opening of the duct for about two thirds of the length of the foot. In Mytilus edidis a stem or ‘rachis’ is formed by the gland which surrounds the duct (Brown, 1952). The secretions of this gland are formed into flat sheets or ribbons as a result of being discharged between numerous lamellae which occupy the blind end of the duct. The secretions are derived from two types of secretory cell. One produces large granules, packed with banded filaments, which are secreted into the crypts formed by the lamellae (Tamarin, 1975). The other produces smaller, cylindroid shaped granules which are secreted along the two faces of each lamella. The stem serves as a point of attachment for collagenous threads, produced in the groove (Mercer, 1952; Pujol, 1967 a, b) by the collagen gland which secretes globules displaying regular banding (Pujol, Houvenaghel & Bouillon, 1972). The proximal end of each thread is attached to the stem by means of a collagenous cuff, each one overlapping the previous one to form a concentric arrangement of cuffs around the stem. The distal ends of the threads are attached to the substratum by a holdfast.

A bass tagging project on the south coast of Anglesey, 1971–5, yielded 86 recoveries from 912 taggings. In addition to expected local movements a systematic pattern of seasonal migration was identified for adults. Fish present in summer moved to south Cornwall for the winter, returning in succeeding summers for spawning. Departure was normally before mid-October. Fish present after that had summered further north (reaching Furness in warm summers). These too moved south as winter advanced, though possibly not reaching Cornwall. A few solitary fish – unfit specimens or members of weak year-classes – appeared to remain through the winter. No evidence was found of movement to, or intermingling with stocks of, the Irish coast; nor, with one exception, the mainland coast of Europe. There was also no indication of movement eastward along the south coast: suggesting discrete populations there from those on the west coast.

The incidence of autotomy is described for a discrete population of Carcinus maenas in the Yealm Estuary over a period of one year. During this time the crabs showed seasonal trends in distribution whereby during the summer months they congregated at the top of the estuary. This seasonal migration up and down the estuary corresponded with peak rates in the rate of change in temperature of the bottom water. Recruitment occurred in June, July and August. Overall, there were more female than male crabs although the ratio varied throughout the year. All sizes and sexes of crabs autotomized limbs but although autotomy increased with the size of the crabs it showed no obvious relationship with other population parameters. Significantly more chelipeds than walking limbs were lost. There were more multiple autotomies than would be expected if autotomy was a random event. Autotomy is shown to be a rare event for sexually mature Carcinus but essential to the survival of immature crabs. The means by which crabs may regulate the incidence of autotomy is discussed.

A number of studies exist on the seasonal cycles of body weight and tissue biochemistry of several species of bivalve from the Clyde Sea area (Ansell & Trevallion, 1967; Ansell, 1974, et seq), including two members of the Pectinidae, namely Chlamys septemradiata (Müller) (Ansell, 1974) and Pecten maximus L. (Comely, 1974). Some comparative data are available for Chlamys opercularis (L.) from Manx waters (Soemodihardjo, 1974) and for P. maximus from the north Irish Sea (Stanley, 1967).

Crassostrea gigas (Thunberg) and Ostrea edulis L. were grown at sustained temperatures of 12°, 15°, 18° and 21°C for a period of 19 weeks. Regular assays of weight specific ammonia excretion rate were made, following which animals were sacrificed for estimation of dry meat weight, dry shell weight, biochemical composition (percentage carbon, nitrogen, carbohydrate, ash) and gonadal development (histological assessment). Crassostrea gigas grew from an intial live weight of 5·2 g to values of 23·5, 28·2, 34·6 and 38·7 g at 120, 150, 180 and 21 °C respectively.

Scanning electron and optical microscopic examination of the hinge apparatus and primary ligament pit of two Recent mytilids (Mytilus edulis and Modiolus modiolus) revealed a similar sequence of ontogenetic changes in both species from the prodissoconch I stage through metamorphosis. Hinge-line dentition was absent at the prodissoconch I stage. Provinculum length and complexity increased throughout larval development with progressive lateral thickening characteristic of the family Mytilidae.

The life-cycles of Corophium volutator (Pallas) and C. arenarium Crawford in the Dovey Estuary are based on two generations per year. Reproduction is well established by April and although the overwintering generation dies during the summer, reproduction continues until October as a result of the breeding of summer-generation animals. The mean brood size of C. volutator is greater than that of C. arenarium and both species show high levels of egg loss from the brood pouch. Hatching and moulting of the embryonic cuticle take place simultaneously and the initial rupture of the egg membranes is made by spines on the cuticle of the telson of the future free-living animal. These spines persist throughout post-embryonic life.

Adult females of both species show a semi-lunar breeding rhythmicity and, associated with this, adult males show a rhythmic pattern of crawling behaviour. As the tide ebbs during the rising spring tide period, adult males emerge from the sediment and crawl across the mud surface in search of burrows occupied by adult females. It is concluded that copulation takes place in the burrow and not in the water column.

In earlier behavioural studies carried out at the Plymouth Laboratory, Pagurus bernhardus L. displayed no activity towards its symbiotic actinian, Calliactis parasitica (Couch) (Ross, 1960; Ross & Sutton, 1961 a). This was in marked contrast to other familiar pagurid/actinian associations, e.g. with Dardanus spp., in which the pagurid participates actively in the transfer of Calliactis to its shells (Brunelli, 1910; Faurot 1910; Ross & Sutton, 1961 b; Ross, 1970, 1974). In the case of P. bernhardus and C. parasitica, laboratory trials showed that contact of the anemone's tentacles with a shell, even an unoccupied shell or one of a living gastropod, releases a sequential behaviour pattern in which the anemone frees its pedal disc and somersaults to the shell. It has been argued (Ross, 1967) that this association exists solely because of the behaviour pattern by which C. parasitica climbs on shells.

There is now a substantial body of evidence that the growth rates of phytoplankton in culture are more closely related to the cellular levels of the rate-limiting constituent, be it a nutrient, micronutrient or toxic metal, than to the concentrations in the supporting medium; nitrate, Caperon (1968); phosphate, Fuhs (1969); silicate, Paasche (1973); vitamin B12, Droop (1968); iron, Davies (1970); mercury, Davies (1974); cadmium, Davies (1978a). This has suggested the requirement for a technique which would allow the determination of comparable relationships for natural populations of phytoplankton - how, for instance, their carbon fixation rates depend upon the metal contents of the plant cells. Although the effects of metals upon carbon fixation in phytoplankton assemblages from several different sea areas have already been examined (Knauer & Martin, 1972; Patin et al. 1974; Zingmark & Miller, 1975; Ibragim & Patin, 1976) no data seem to have been obtained on the levels of the metals present in the phytoplankton at the time of the measurements.

In a study of the breeding biology of Euchaeta norvegica (Boeck), Hopkins & Machin (1977) analysed the placement and frequency distribution of spermatophores on females. They found the number of spermatophores on sampled females to be underdispersed relative to the Poisson distribution and concluded that ‘virgin’ females are more attractive to males than females with spermatophores attached. They fitted the Greenwood & Yule (1920) model but drew no conclusions.

The type of question which may be studied by fitting such a model is whether the attraction of males to ‘non-virgins’ is independent of the time since the first spermatophore was attached and also independent of the number of spermatophores already attached. This problem has been further investigated by fitting a version of the Greenwood & Yule model based on asynchronous recruitment of mature females. This version of the model is fully described in Schweder (1979); in this paper the results and biological implications are discussed.

Patterns of cell elongation and differentiation were examined in a number of Audouinella spp. In all species examined, cells reached their maximum length within a few cells of the apex after which the length (and diameter) of cells became stable. No size differentiation of cells associated with lateral branches was observed, although the basal cells of lateral branches were usually smaller than those in the main axis (except in A. purpurea (Lightf.) Woelkerling and A. parvula (Kylin) Dixon). The position of the lateral branches on branch bearing cells showed little variation and could be used to develop quantitative characteristics for species delimitation. Early stages of development in A. secundata (Lyngbye) Dixon showed an increase in size of apical and subapical cells with plant height, with cell length decreasing toward the base. These developmental features confirm the simple morphology of Audouinella spp, and show that models of growth and differentiation proposed for the Ceramiaceae generally do not apply to the Acrochaetiaceae.

The Phylum Chaetognatha consists of morphologically and biologically similar species and its relationship with other invertebrate groups is obscure (Hyman, 1959; Ghirardelli, 1968). The possibility of regenerative power has been investigated as one of the clues to the affinity of the phylum. Kulmatycki (1918) made cross-sectional and diagonal cuts through the body and tail fin of Spadella cephaloptera Busch and reported that this species could regenerate the whole caudal section including the body proper. Further support for regenerative ability came from Pierce (1951) who caught 26 specimens of Sagitta enflata Grassi and Sagitta helenae Ritter Zahony which appeared to be in the process of regenerating their heads (presumably lost to a large predator). He noted that the loss of this section of the body did not kill the animal. Both Kulmatycki and Pierce are cited in Hyman's (1959) important review of the phylum and headless chaetognaths have been referred to as animals with regenerating heads (e.g. Almeida Prado, 1968).

The salinity of the water retained within the mantle cavity of mussels after the shell valves have closed in response to falling environmental salinities is influenced by the rate of external salinity change. At high rates of salinity change the retained water salinity is significantly higher than in animals exposed to slowly changing salinities. However, the mantle fluid salinity is not primarily determined by the timing ofx shell valve adduction, but by closure of the exhalant siphon.