Eighty-seven specimens of Bathothauma lyromma from the ‘Discovery’ collections have provided new information on this unusual species. The size range represented is sufficient to trace the development from small larvae to near adult. Information on sexual development is also given. Twenty-nine specimens from opening-closing nets show that Bathothauma occupies the depth range 100–1250 m, with smaller specimens living at shallower depths than the larger ones.

As the processes by which epiphytic bryozoans become established in aggregations on intertidal algae become more clearly understood, it is necessary to consider some of the ecological consequences of non-random settlement. The adaptive significance of aggregation in epiphytic bryozoans has been discussed recently by Hayward & Ryland (1974), who also showed how the worst effects of overcrowding are mitigated. Acorn barnacles and spirorbine tubeworms have evolved a specific behavioural pattern which results in regular, spaced-out settlement within aggregations, thus allowing room for each individual to become established and begin growing. By contrast, epiphytic bryozoans do not exhibit this kind of behaviour (Harvey, Ryland & Hayward, in preparation). Al-though a minimum size is probably required before the colony is able to breed, the pattern of growth observed for Alcyonidium hirsutum shows that this can be achieved through lability of growth direction. The linear relationship found to exist between colony size and fecundity shows that no advantage is conferred by increased size; the smaller colony is as effective in reproduction as the larger. In the present paper two other ecological consequences of aggregated settlement are considered: mortality and size.

The biochemical composition of three batches of Ostrea edulis L. spat was determined during post-settlement growth. The spat were from spatfalls in January, March and June. For the first few months after settlement the neutral lipid (triglyceride) content was greater than the glycogen content. However, in three- to five-month-old spat the glycogen content became greater than that of neutral lipid.

Hydrobia ulvae has featured in many reports on the ecology of estuaries and mud-flats, yet surprisingly there are few detailed studies on population structure, growth and the breeding cycle. Population densities fluctuate widely from one locality to the next, and the variation in size recorded for the adults suggests significant differences in growth rate and the size at which the snails become sexually mature. The occurrence of Hydrobia in the stomachs offish and birds is well documented (Clay, 1960) and the suggestion that this species may influence the breeding success of some species of bird (Anderson, 1971) illustrates its importance in the ecology of estuaries and salt marshes.

During recent years attention has been focused on the morphology of the bivalve digestive gland (Sumner, 1966a, b; Owen, 1970; Pal, 1971,1972) but there is little information concerning its role in the storage of energy reserves. Reid (1969) has suggested that in the horse clam, Tresus capax, digestive gland lipid may serve as an energy store which is depleted when food is scarce. Sastry (1966) and Sastry and Blake (1971) have shown that material stored in the digestive tissue of Aequipecten irradians is transferred to the gonad during gametogenesis and Vassallo (1973) has confirmed the transfer of lipid in Chlamys hericia. The digestive gland of My tilus edulis may also have a storage function and may therefore be involved in the utilisation of reserves during starvation. The present paper deals with seasonal changes in the biochemical composition of the digestive gland of M. edulis, and with changes induced by starvation and temperature stress.

A number of species of the family Pectinidae (Lamellibranchia, Mollusca) are of considerable commercial importance in many parts of the world. Many of these are being reared in laboratories and hatcheries and this has made easier studies of cytogenetics using eggs and embryos, and ultimately will make studies of their genetics feasible. Recently, simple squash techniques have provided a fast and reliable method for obtaining chromosome numbers from eggs and embryos of several bivalves including Mercenaria spp. (Menzel & Menzel, 1965), Ostrea lurida and Crassostera gigas (Ahmed & Sparks, 1967), Mytilus spp. (Ahmed & Sparks, 1970), and Crassostrea spp. (Menzel, 1968). In 1967, Longwell, Stiles & Smith published the karyotype of Crassostrea virginica obtained from embryos which had been treated with colchicine.

Interest has developed recently in the biochemical composition of zooplankton, particularly in relation to seasonal changes. An earlier study (Raymont, Srinivasagam & Raymont, 1971b) on deep frozen Antarctic krill, Euphausia superba, collected over approximately 5 weeks in December/January 1968/69 suggested that protein was the main constituent and lipid much more variable. Despite the variability the mean lipid content during January was distinctly higher than in the previous month, thus supporting the findings of Kryuchkova & Makarov (1969) that lipid content of krill tends to increase as the summer advances. However, collections of material from the Antarctic have tended to be limited both in location and season while methods of preservation have varied. It seemed desirable to follow changes in the biochemical composition of krill collected from a somewhat wider area and over a longer period. Moreover, the more extensive material gave opportunity for a more detailed examination of specific fractions, such as the amino acids of Euphausia superba. Preliminary investigations (Srinivasagam, Raymont, Moodie & Raymont, 1971) on the amino acid composition of protein hydrolysates showed good agreement with the results of some other authors. However, the findings of Burkholder, Mandelli & Centeno (1967) and especially of Moiseev (1970) showed certain differences.

Jaera nordmanni (Rathke) occurs abundantly beneath stones and algae in freshwater streams (McCartan & Slinn, 1953), brackish water pools (Naylor & Slinn, 1958), and estuaries (Naylor, Slinn & Spooner, 1961; Harvey, Jones & Naylor, 1973). The species is widely distributed and ranges from the Black and Mediterranean Seas south to the Azores, and north to the west coast of Scotland (Naylor, 1972). Three forms of J. nordmanni have been described (Lemercier, 1958, i960) of which only Jaera nordmanni nordica Lemercier has been recorded in Britain (Naylor, 1972; Jones & Fordy, 1973). The two other forms, Jaera nordmanni nordmanni Lemercier and Jaera nordmanni massiliensis Lemercier, have a more southerly distribution (Naylor, 1972), and can be separated from J. nordmanni nordica by differences in male sex characters (Lemercier, 1958, 1960; Jones & Fordy, 1973). Apart from some eco-physiological work (Naylor et al. 1961; Harvey et al. 1973) and a recent study with a scanning electron microscope (Jones & Fordy, 1973), little is known of the biology of J. nordmanni. The present paper reports on the breeding biology and seasonal population fluctuations of Jaera nordmanni nordica, and compares the results with a similar study on the members of the Jaera albifrons Leach group of species (Jones & Naylor, 1971) which are closely related to and often in competition with J. nordmanni.

The isopod genus Jaera Leach (Crustacea) is a common component of the fauna in estuaries (Green, 1968; Jones & Naylor, 1971; Naylor, 1972; Jones, 1974). The members of this genus are able to survive low salinity (Jones, 1972a; Harvey, Jones & Naylor, 1973) by active control of the osmotic concentration of the body fluids above that of the external environment (Jones, 1972&; Forbes, 1974). While it has been well established that the crustacean gill is the site of the transport system involved in osmoregulation (Koch, 1954; Shaw, i960; Bielawski, 1964; Croghan, Curra & Lockwood, 1965; Quinn & Lane, 1966), there have been few studies on the fine structure of this organ (Copeland, 1968; Copeland & Fitzjarrell, 1968; Bielawski, 1971; Fisher, 1972; Talbot, Clark & Lawrence, 1972; Lockwood, Inman & Courtenay, 1973). The present paper describes the structure of the gills of Jaera nordmanni (Rathke) and relates the role of the various elements observed to the physiological functioning of the gill.