Vertical and horizontal hauls were taken at approximately fortnightly intervals from April 1969 to April 1970 at L 3 (lat. 40° 17.7′ N, long. 4° 11.2′ W) and L 4 (lat. 50° 15′ N, long. 4° 12.5 W). Thirty-two species of prosobranch veliger were present at L 35 these larvae were not as numerous at L 4 and only 26 species were recorded. The number of species was highest in the summer: the number of veligers was highest in February. After mid October both the number of species and the abundance of veligers decreased rapidly and remained low until early February. Veligers of some species occurred later at L 3 and L 4 than in more inshore waters and these were probably individuals carried beyond tidal influences which would normally lead to settlement on the shore. They included Lacuna vincta, Littorina littorea and L. neritoides.

Veligers of all ages were found at all depths. At their time of greatest abundance veligers of many species occurred maximally at 5 or 10 m, with a variable decrease towards greater depths and a sudden one towards the surface. This distribution later changed giving a proportionally greater number at greater depth. When numbers were low the larvae scattered through the water column with little or no indication of a preferred depth. An examination of the age composition of veligers of rissoids, Natica alderi, Nassarius reticulatus and Philbertia linearis from certain catches showed that the surface accumulation at the time of abundance was composed of a high percentage of young veligers: in an ageing population there was a higher percentage of larvae, especially the older ones, at greater depths, except for Nassarius reticulatus which consistently showed maximal numbers above 10 m until the larvae became scarce.

L. pallidula is more or less confined to Fucus serratus. L. vincta is common on F. serratus but is also found on Halidrys, Laminaria and various Rhodophyceae. Neither species occurs in the absence of these weeds on which they both feed and spawn. Lacuna species are the dominant gastropods on weed at M.L.W.S. at Whitburn, County Durham.

Both species are annuals. In L. pallidula the growth rates of females and males are markedly different, the former growing both faster and over a longer period. Females attain a mean maximum size of 8–4 mm compared with 45 mm for males. L. vincta males and females grow at approximately the same rate, though females usually attain a greater size.

Males predominate in L. pallidula at all times of the year, comprising between 55% and 75% of the population with a mean of 68–6%. Males die slightly sooner than females but there is no more than 4 weeks difference in longevity. Copulation in L. pallidula begins in November and continues to April, with two peaks in January and March.

Spawning commences in January in both species and reaches its peak by April in L. pallidula and by June in L. vincta. Hatching occurs in L. pallidula from April to July. The time of first hatching in L. vincta is not certain but is probably about March. Larval settlement occurs from June to October with a maximum in September.

Density is high following hatching in L. pallidula (> 2000/m2) and settlement in L. vincta (> 300/m2). Dispersion is similar in the two species, being aggregated at high density and more or less random at low density.

The ‘mucous’ tube of Platynereis dumerilii is made up of successive layers of fine threads held together by an adhesive secretion. Tube construction involves a regular sequence of behaviour which can be modified if algae or other objects are available for incorporation into the tube wall. Anterior parapodia are specialized for tube construction and gland cells producing tube components occupy most of the coelom in these segments. Several types of gland cell can be recognized histologically and those which form the threadsdischarge into a complex spiral organ below the cuticle.

A nocturnal larval hatching rhythm is described for the lobster Homarus gammarus. In natural illumination cycles, hatching takes place shortly after darkness with the hatching process lasting for about 1 min or less. One female lobster can release batches of larvae each successive night for periods of from 2 to 6 weeks, depending on size and water temperature during the period of hatching. The hatching rhythm persists, though slightly out of phase, when lobsters that have been releasing larvae for some time are kept in constant darkness, but in constant illumination hatching may be delayed for 2 or 3 days and when it does occur it is erratic and non-rhythmic. Larvae that do hatch in constant illumination appear to do so without parental assistance. Onset of darkness synchronizes the rhythm but an endogenous component is involved in controlling it.

Analysis of the carotenoid pigments of decapod crustaceans has indicated that the visible differences in the appearance of species from different depth horizons are largely due to the disposition of pigments and not to differences in total amount of pigment relative to body size. Species from the upper mesopelagic zone have relatively few large chromatophores, and their chitin is either unpigmented or feebly pigmented. Species from deeper zones have very many small chromatophores and chitin heavily pigmented by unesterified astaxanthin. The major carotenoid pigments of almost all species are astaxanthin and its esters.

Lipid analyses have shown that several species of Caridea have very high levels of lipid in the body, and that in many deep-water species wax esters comprise a large proportion of the total lipid. Specific patterns of distribution of the various lipid classes are found in different tissues, with wax esters particularly dominating the hepatopancreas lipids of deep-living species.

The patterns of pigment and lipid distribution are discussed in relation to the depth distribution, light environment, and metabolic requirements of the different species.

A critical evaluation of the characters utilized in support of a report of hybridization between two sympatric European species of Pagurus is presented. These characters are contrasted with characters considered to be diagnostic for the species. Although, on the basis of present evidence, the possibility of hybridization is not wholly excluded, it is shown to be highly improbable.

Adult female mysids do not moult while carrying young in the marsupium. Successive larval stages can be recognized in the marsupium and this allows examination of the body length of the parents at different points in the inter-moult period. The body length of 13 species of mysids was found to have increased during the course of the inter-moult period; the average increase in length of the body is 7%. An examination of the ratio of abdomen length to carapace length at different points in the inter-moult period shows that this growth in length is accommodated in the abdomen.

The hydroid of the medusa Modeeria rotunda (formerly Tiaranna rotunda) has been found to be the thecate species Stegopoma fastigiatum. The medusa has been obtained from the hydroid and reared to maturity. The stages of development of the medusa are described and figured, and its occurrence and habits are discussed. The affinities of the medusa are considered: it is shown to belong, together with the the genus Chromatonema, to the family Laodiceidae.

The hydroid, hitherto unknown, of the leptomedusa Mitrocomella polydiademata has been reared from medusae collected in the Firth of Clyde. The growth and structure of the hydroid and the stages of development of the medusa are described and figured.

Three specimens of Stygiomedusa fabulosa Russell, 1959, identified recently in the collections of the Zoology Department of the British Museum (Natural History) (Table 1) extend the recorded distribution of this infrequently collected genus to the Southern Ocean, and provide the opportunity of assessing the specific distinctness of S. stauchi Repelin, 1967. The specimens are the first of either species recorded from south of the tropics.

The largest recorded specimen of the mesopelagic scyphomedusa, Stygiomedusa fabulosa Russell 1959, was taken in the North Atlantic (49° 53' N, 33° 18' W). Umbrella diameter was 140 cm with an oral arm length of 164 cm. This specimen is morphologically intermediate between the nominal species of the genus, S. fabulosa and S. stauchi. This suggests that S. stauchi is not a distinct species. The midwater fish Thalassobathia peligica was captured in the same haul and could live in association with large scyphomedusae.

The buoyancy, lipid levels, and orientation of five species of myctophid from the Biscay area were examined, and it was found that two of the five were probably normally denser than the sea water in which they live. Analysis of the swimbladder gas of Myctophum punctatum collected at the surface at night indicated that this species has a less extensive vertical range in this area than elsewhere. A functional classification of myctophids is proposed, based upon density, lipid levels, and the presence or absence of a gas-filled swimbladder.

The movements of herring and plaice larvae of different age, from hatching to about 8 weeks old, were monitored at different levels in a vertical tube by means of matched pairs of thermistors controlled and ‘balanced’ by bridge circuits. Movement of larvae past the thermistors upset the balance and the resulting change in the circuit could be followed on a pen-recorder. Having established, by visual comparisons, the interpretation of the pen record, experiments could be performed over extended periods or at low light intensities when visual observations would have been tedious or impossible. The numbers of larvae present were shown by the number of spikes on the pen record per unit time, while a measure of their size or activity was given by the height of the spikes.

The light intensity could be altered by interposing neutral-density filters between an artificial light source and the surface of the tube. Alternatively, natural daylight could be beamed in by a mirror above the tube when placed by a window. Using artificial light, changes of very large intensity had little effect on the larvae until a critical level was reached (equivalent to the intensity at late dusk or early dawn) when a vertical migration took place. A similar vertical migration took place when the natural light at dusk was beamed in; many larvae then moved to the surface and remained there, apparently very active throughout the night untill the light increased at dawn. Vertical migration could be simulated in the laboratory at any time by imposing an artificial light-cycle of appropriate amplitude on the larvae.

Neutral lipid classes were analysed in the livers, muscles and sera of Deania, Centroscymnus, Squalus and Prionace. All three squaloid sharks contained triglycerides and alkyldiacylglycerols and the two deep sea squaloids contained additionally hydrocarbons. Prionace contained triglycerides and hydrocarbons but no alkyldiacylglycerols. For a given species the class compositions of the lipids were similar in liver, muscle and serum, except that serum contained additionally cholesteryl esters and wax esters. Cholesteryl esters in Squalus serum were rich in oleic acid whereas wax esters were very rich in polyunsaturated fatty acids. Squalus serum contained a major and a minor lipoprotein species both of which transport all four neutral lipids in serum. It is concluded that, with the exception of cholesteryl and wax esters in serum, neutral lipids are distributed between shark tissues by a mechanism that is relatively non-specific with respect to lipid class.

A series of controlled, labelled feeding experiments were carried out on Neomysis integer in order to investigate its lipid metabolism. The techniques of thin-layer chromatography, preparative column chromatography, analytical and preparative gas-liquid chromatography and low-background 14C counting were used to follow the incorporation of a 14Clabelled fraction from a range of diets into the animal's lipid. Neomysis integer was found to be capable of converting dietary starch or short-chain saturated fatty acids to longchain polyunsaturated fatty acids, which were then incorporated into the TG and PL fractions.

Light and electron microscopy showed the same distribution of glycogen. The peritoneal cells contain large amounts in all three body regions investigated: the forepart, metameric region and postannular region. Glycogen is present in most epidermal cells and is very abundant in some, particularly in the postannular region, but the cells which secrete the chitinous and proteinaceous components of the tube are almost devoid of glycogen.

Adult European flat oysters, Ostrea edulis L., receiving a food supplement of the unicellular alga Tetraselmis suecica (Kylin) Butch, during laboratory conditioning for spawning produced more broods of larvae than oysters receiving only the natural phytoplankton in the seawater supply. Many of the broods from adults receiving this extra food were liberated sooner, and these larvae grew at an enhanced rate and provided greater spat yields than the broods from the control stock. The viability of larvae, which was significantly correlated with their lipid, and in particular neutral lipid, proportion at the time of liberation, declined as the length of the stock-conditioning period prior to female spawnings increased. This may be related to the decline in the dry meat weight and the condition factor of the adult oysters during the experiments irrespective of the feeding regime. The extra algal ration provided a check to the decline in dry meat weight of the food-supplemented adults.

Recent equations for calculating the osmotic coefficient of sea water from the properties of the component single-electrolyte solutions are discussed. Two equations are introduced that together provide accurate predictions of the osmotic coefficient of sea water for ionic strengths up to 4 M (equivalent to a fivefold concentration of standard sea water). Since they take into account the detailed solution composition these equations should be useful for calculating the osmotic coefficients of estuarine waters and of biological salines where procedures based on curve fitting to standard sea-water data may be inapplicable. Extensions of the calculations to cover a wide pressure and temperature range are discussed in some detail.

A seasonal survey of particulate and dissolved organic material was made at E1 in the English Channel during 1968. The average integral mean values were: dissolved organic carbon 65 μg-at C/l (780 μg C/l); dissolved organic nitrogen 4·6 μg-at N/l (64 μg N/l); dissolved organic phosphorus 0·12 μg-at P/l (3·8 μg P/l); particulate organic carbon 190 μg C/l and particulate organic nitrogen 21 μg N/l. Dissolved organic carbon and the particulate organic carbon and nitrogen showed increases subsequent to the spring bloom; such increases were less evident in the dissolved organic nitrogen results and not apparent in those of dissolved organic phosphorus.

Analyses were also made in March and June in 1969 at two other stations in the English Channel, in addition to E1. The results from the three stations were basically similar.

Concentrations of copper, zinc, lead, manganese and iron in the brown seaweed Fucus vesiculosus have been measured in samples collected over its range of distribution in four estuaries having different degrees of metal contamination. Factors controlling the concentrations in the weed have been studied and include the concentrations of metals in the water, seasonal changes, the position of the weed in the intertidal zone and the particular portion of the plant which is analysed. It is concluded that analysis of the weed gives a reasonable indication of average conditions in the water at points along an estuary and provides a method of making comparisons with the same estuary in subsequent years or with other estuaries.