The closure response to low external salinity of three species of intertidal and estuarine barnacle (Balanus balanoides, B. crenatus and Elminius modestus) when exposed to various rates of salinity change were investigated. Comparisons were made between the responses of specimens collected from estuarine and coastal sites. In addition the responses of the brackish water barnacle Balanus improvisus were measured.

The morphology and ultrastructure of the heart and excretory system of the marine lamellibranch bivalve mollusc, Mytilus edulis (L.) are described. This paper supports the view that ultrafiltration of the blood occurs in the pericardial cavity. The auricles, pericardial glands and afferent oblique veins contain podocytes which are usually ascribed to the specific function of ultrafiltration. These cells are absent in the ventricle. The pericardial cavity communicates with the exterior via a very short (ca. 1–2 mm) renal tubule. The kidney comprises of a series of highly branched diverticula of this tubule and displays little or no structural differences throughout the organ. The kidney cells form a single layered columnar epithelium with a brush border, basal nuclei, infolded basal membranes and are characterized by the presence of many membrane-limited granules occupying as much as 20% of the cell volume. These granules and those of the podocytes are subsequently shed into the lumen of the kidney tubule and are excreted in the urine which is therefore largely paniculate.

The composition of subtidal meiobenthic associations off the Isle of Man is analysed, with particular reference to the harpacticoid copepods. By comparisons with surveys in other seas it is suggested that coherent associations of benthic copepods can be recognized in the sublittoral fringe area of tidal fine sand beaches and in offshore fine sand in Europe. The heterogeneity of offshore coarse deposits and muddy sands results in the inability to distinguish communities or isocommunities in these deposits. As muddy sand grades into mud some evidence is presented to suggest that, given similar temperature and salinity regimes, a consistent association of copepods may develop.

Zinc (Zn II) and iron (Fe III) were demonstrated histochemically in cytoplasmic inclusions shown to be lysosomes in a number of cell types in Mytilus edulis. The cellular distribution of the metals differed between the sexes; males were shown to have more zinc (Zn II) in the kidney than females, the latter appearing to use oocytes as an additional means of excretion. Differences in cellular distribution of the metals was also demonstrated between the two populations studied probably reflecting availability of the metals in their respective environment.

Gills of fresh-water and sea-water eels were perfused at a constant pressure with physiological Ringer containing 10−6 M sodium orthovanadate and examined by light microscopy. The secondary gill filaments were markedly vasoconstricted in both freshwater and sea-water fish although the peripheral blood route around the secondary filaments was unaffected. The central venous space in the primary filament was largely unaffected. Significant constriction of both afferent and efferent arteries on the primary filament occurred. We conclude that orthovanadate vasoconstricts eel gills mainly at the level of the secondary filaments. The study also emphasizes that chloride cells are located on both the primary and secondary filaments of fresh-water gills but solely on the primary filaments of sea-water gills.

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 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.

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.

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.

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.

A karyometric analysis of the diploid complement of two species of the genus Procerodes (Tricladida: Maricola), both from British waters, has been carried out

The diploid number of Procerodes littoralis, 2n = 14, was established on mitosis from regenerative blastema and the haploid number n = 7 from spermatocyte I stages. All the chromosomes are metacentric, their centromeric index varying from 47·91 in the chromosome 5 to 38·39 in the chromosome 4.

Analyses of the jaws of nereid polychaetes have shown zinc to be a major inorganic component amounting to between 0·5 and 2·4% of the dry weight and accounting for up to 40% of the total body burden of zinc. In Nereis diversicolor, zinc concentrations in the jaws are not related to those of the habitat sediments. A high zinc content appears to be a structural characteristic of the nereid jaw.

Contradictory evidence has led to contrasting hypotheses as regards the origin in Actinia equina. L. of the juvenile anemones which may be found being brooded within adults. We have found, in a North Yorkshire population, a very low proportion of males, but these, as well as individuals lacking gonads, often contained young. All young resembled in colour the adults from which they were obtained. Adults maintained in isolation so as to prevent fertilization continued to produce young. Also ova apparently undergoing cell division were found within female gonads. By contrast, small fragments of anemone, although adopting the appearance of larvae, when cultured, do not develop into juveniles. We conclude that within the population studied reproduction is most probably by parthenogenesis.

Evidence is presented from a study of Actinia equina var. mesembryanthemum at Bembridge, Isle of Wight, which suggests that brooded young do not represent a random sample from a free-living larval pool. Parents in the laboratory will not accept juveniles placed on their oral disc. A. equina are, therefore, unlikely to be adoptive parents. Esterase heterozygote parents contain only heterozygote young. Sexual reproduction cannot account for this observation unless a parent selects its brood. As A. equina can distinguish self from non-self and juveniles may reproduce asexually, a fertilization - selection - cloning theory of reproduction is considered which could account for what is otherwise a conflicting body of evidence.

The hydrodynamic properties of the shell of Chlamys opercularis have been investigated and compared with other Pectinidae. The coefficient of lift increases with increasing current speed and angle of attack. Little benefit is gained by increasing the angle of attack beyond 20 °. Allometric changes in shell shape are not sufficient to counteract the increasing weight of the animal with growth. Flow patterns over the shell indicate that a smooth and attached flow over the body of the shell becomes broken up into a turbulent, eddying wake at angles of attack beyond 20 ° and at current speeds greater than 25 cm s−1. The effect of the auricles is to enhance lift at low speeds and to help maintain stability. It is postulated that large turbulence may be further reduced if the dorsal jets act as jet flaps.