Coccolith structure, mode of origin and arrangement on the cell surface have been investigated in two marine coccolithophorids, Coccolithus pelagicus (Wall.) Schiller and Cricosphaera carterae (Braarud et Fagerland) Braarud, by means of light microscopy and electron microscopy of whole mounts and sections. The presence of flagellar bases in Coccolithus pelagicus is also demonstrated in spite of the fact that the cells of this phase of the life-history are non-motile. In both organisms the coccoliths are shown to be accompanied by unmineralized scales, details of which are illustrated; in particular, each coccolith is attached to the margin of an unmineralized oval plate which completely covers the central ‘pore’ on the side towards the subtending cell. Scales and coccoliths arise within the cisternae of the single Golgi body in a manner closely resembling the origin of scales in species of Chrysochromulina. It is therefore suggested that the coccoliths of the two taxa investigated can be interpreted as modified (and calcined) scale rims.

The diet and feeding mechanisms, digestive processes and nature and distribution of the food reserves of the entocommensal rhynchocoelan Malacobdella grossa (O. F. Müller) have been studied by histological, histochemical and biochemical methods.

The species is predominantly an unselective microphagous omnivore and possesses two distinct feeding methods. Small particles such as bacteria, algae, diatoms and protozoa constitute the bulk of the diet and are filtered from sea water by means of a pharyngeal ciliary mechanism that does not involve the use of mucus; larger particles, mainly crustacean larvae, are caught by the proboscis and subsequently ingested intact without further treatment.

Digestion occurs in the intestine and combines extra- and intracellular processes which involve mainly carbohydrases apparently secreted by gastrodermal gland cells. This emphasis on carbohydrate digestion, atypical in rhynchocoelans, can be correlated with the species diet.

Fat and glycogen constitute the food reserves, with the former being the principal store and mainly deposited within the gastrodermal columnar cells.

The swimming musculature of spinal dogfish, Scyliorhinus canicula (L.), was paralysed with curare while recordings were made of the motor activity in the abdominal spinal nerves. Spontaneous, periodic motor bursts of long duration and decreasing frequency were detected during the first 2 h or so of the experiment. The spinal neurons were incapable of sustaining motor activity for more than 1 or 2 h and were dependent on proprioceptive feedback to maintain their excitability; their discharge frequency could, however, be enhanced by un-patterned sensory stimulation.

The spinal neurons on each side of the cord are sufficiently organized to dis-charge alternately but the longitudinal co-ordination of the locomotory wave is disrupted in the absence of phasic sensory excitation.

INTRODUCTION

It has been assumed that the locomotory movements of spinal dogfish, which persist with undiminished vigour for several hours, are co-ordinated in one of two ways. One possibility is that the entire periodic motor output is formulated by the nerve cells of the spinal cord (Gray & Sand, 1936 a, b; Le Mare, 1936); alternatively, it is conceivable that the motor pattern is triggered by sensory signals fed back to the spinal cord by proprioceptors stimulated during locomotory movements (ten Cate, 1933; Lissmann, 1946a, b).

Lissmann attempted to distinguish between these two general hypotheses by cutting all the dorsal roots of spinal dogfish and thereby isolating the spinal neurons from sensory stimulation. His experiments showed that the spinal animal would swim normally even when a considerable number of dorsal roots had been sectioned but as complete de-afferentation produced im-mobile preparations he concluded'that the motor rhythm was ultimately dependent on proprioceptive activity.

The locomotory musculature of dogfish is innervated by the segmental spinal nerves. The sensory and motor innervation of the abdominal musculature was studied in a preparation consisting of a strip of the abdominal body wall innervated by the ventral rami of the spinal nerves.

Each ventral ramus consists of two separate nerve bundles which were found to be peripheral extensions of the dorsal and ventral spinal roots. Recordings from the sensory bundles showed that there are few sensory endings in the musculature and body wall of the dogfish. It was possible to differentiate between ephemeral responses produced by cutaneous free-nerve endings and prolonged discharges which were generated by more specialized sensory endings. In some details these endings were found to be unlike either muscle spindles or tendon organs. Further, skinning experiments suggested that these mechanoreceptors lay in the skin or the very outer layers of the myotome.

Histological searching, together with physiological isolation of units, suggested that these receptors were the corpuscular endings distributed sparsely amongst subcutaneous tissue. These endings are apparently the same as those described by Wunderer (1908) in the fins of elasmobranchs.

The life-history of the larva of the prawn Palaemon serratus (Pennant) was studied in the laboratory and found to comprise a variable number of stages, dependent on feeding level and other factors. Larval moulting frequency was relatively constant at 3-day intervals, and could be followed in a population by daily examination for exuvia moult-casts. Length increase at each moult progressed arithmetically, and the highest mortalities occurred during metamorphosis. Consumption of Anemia nauplii by each larva rose from 30 to 400 per day. Populations of isolated animals (i.e. when cannibalism was excluded) were inspected daily and the exact number and duration of larval stages determined. Survival through metamorphosis was very high (over 85%) at both high and low feeding levels, although at the latter the larvae passed through more stages with more erratic duration times. At the end of the experiment, when all the larvae had metamorphosed, the mean dry weights at the high and low feeding levels were 7.7 and o.6 mg respectively. Larval stages could not be positively identified morphologically after stage III unless the history of the individual in question was known. It is suggested that the number of larval stages in the sea may also be very variable and difficult to determine.

Energy-conversion efficiency was calculated from food uptake measurements and larval growth estimations, and was found to be 50–60% during most of the larval life, falling to 35% when the early post-larvae were taken into account.

A range of 27 marine phytoplankton species, representative of several of the principal classes, has been grown under similar conditions in Erd-Schreiber medium with abundant nutrients. Harvesting was carried out 20 days after inoculation while vigorous growth was proceeding. The component fatty acids of the lipids extractable with chloroform-methanol were determined by gas-liquid chromatography. In all, 40 fatty acids were determined. It is likely that the component fatty-acid distribution may be valuable for taxonomic purposes. Thus, specific fatty-acid assemblages may characterize particular Phyla or even classes. For example, the Bacillariophyceae are differentiated from the other organisms examined by the virtual absence of 18:2, 18:3 and 1814; the Cryptophyta are distinguished by their high content of 20:1. The fatty-acid arrays of species belonging to the same genus are frequently very similar, e.g. Dunaliella primolecta and D. tertiolecta.

An investigation has been made of the occurrence of 25 amino acids in the hydrolysates of five species of diatoms which had been grown in Erd-Schreiber medium. Their distribution pattern in general resembles that found in other species. However, there are characteristic differences; thus, they contain more serine and 2-amino iso-butyric acid than the other species of phytoplankton.

The adults ofNereis fucata (Savigny) are commensal with hermit crabs and live within the upper whorls of the shells of their hosts. The mechanism of host adoption has been examined in juveniles reared in the laboratory. There are two distinct phases in their response to their host. The first is a searching phase during which the anterior two-thirds of the worm is extended from the tube and makes wide sweeping movements in its immediate vicinity. This phase can be initiated in the laboratory solely by vibrations in the substrate; the presence of a hermit crab is not required. The second phase begins as soon as a suitable gastropod shell is touched, when the worm immediately leaves its tube and enters the shell. In the laboratory this phase can be achieved without the presence of a hermit crab, so that it is presumably primarily dependent upon the tactile stimuli received from the surface of the shell. It is argued that in nature only hermit-crab shells would commonly give this combination of stimuli to the worm and that the association betweenNereis fucata and hermit crabs is not accidental but commensal.

The new species Halosphaera parkeae (Prasinophyceae) is described from material collected in the western English Channel. The microscopical structure of the outer wall of the non-motile phase is described and two types of punctation are demonstrated. A general account of the cytology of the mature non-motile phase and of the motile cell is given. Electron micrographs of the scales of the motile cell are compared with those of other species of the genus where known. Buoyancy, size and reproduction are discussed and a number of new taxonomic characters emphasized. The occurence in the same areas of a second type very similar but smaller in size is recorded and the authors have named this form Halosphaera parkeae forma minuta.

Vitellogenesis in S. borealis is described. The large protein yolk spheres consist of protein and lipoid. This comes by pinocytosis from outside the oöcyte and from the golgi within the oöcyte. This is discussed in relation to other animal oöcytes. Cortical granules are present at the periphery of the oöcyte and release their contents just before the egg leaves the coelom. When released the eggs have an envelope around them, and evidence is presented which suggests that it is formed from material produced by secretory cells around the exit hole and along the ciliated groove.

Cucutnaria elongata Düben & Koren, collected from the Northumberland coast in January 1968, was induced to spawn in the laboratory by raising the temperature. At spawning, the animal waved its pharyngeal bulb back and forth while a thin string of gametes was discharged. The freshly spawned eggs, surrounded by a jelly coat, were at the end of the second meiotic division and the size varies from 250 to 350 μ in diameter. Oocytes in the ovarian tubules can be grouped into three stages according to their size and other morphological features. Insemination of artificially recovered eggs resulted in only a very low frequency of abnormal development up to 8-cell stage. However, over 90% fertilization was achieved by insemination of the naturally shed eggs and the development was normal. The cleavage was holoblastic and radial type. The larva hatched at post blastula stage and swam freely with its animal pole upward. A doliolaria stage with four ciliary bands and pentactula stage with five primary tentacles subsequently developed. The planktonic life at temperature 9–11 °C ended on the ninth day after fertilization. Pentactula, up to 4 months old, live underneath the mud where they are deposit feeders. The primary tentacles bearing mucus glands in the form of papillae are important in both locomotion and feeding. An outline of chronology from fertilization up to 5 months old is presented.

The biochemical constituents of mussels both infected and free from the copepod parasite Mytilicola intestinalis Steuer have been determined over a period of 2 years. All the constituents except moisture content (i.e. lipid, protein, carbohydrate and ash) were determined from dried mussel flesh, and all showed seasonal variation, the changes of which were correlated to the breeding cycle of the mussel.

The distribution of Laminaria ochroleuca along the south-west coast of England and the Isles of Stilly is brought up to date. The pattern of distribution is discussed with reference to certain factors controlling the ‘ performance’ and success of the species on the northernmost edge of its range. The performance of individuals of the species (measured as net stipe production) sampled from populations growing on the coast of south-west England is compared with populations from north-west Spain, where it is growing in the centre of its geographical range.

The degree of exposure to direct onshore wave action appears to govern the upper limit of its bathymetric range as well as its distribution along the south-west coast of England.

It was found possible to age this species using the method and precautions described by Kain for Laminaria hyperborea.

The stipe material sampled from the English populations had a higher ash content per gram dry weight and a higher calorific content per gram of organic material than that from the Spanish populations.

Individuals from the English population had a lower weight per unit length of stipe in all age-classes than those from Spain.

It is suggested that incident radiation may be a more important factor than temperature in controlling the northward limit of the species.

The lesser argentine, Argentina sphyraena L., is a Mauretanian-Mediterranean-Boreal species extending from about 68° N. off the Norwegian coast to 25° N. off Spanish West Africa. It is most commonly caught on the offshore continental shelf in depths between 50 and 100 fm where average sea temperatures of 6° and 17°C are encountered at the northern and southern limits respectively of the species geographical range. Larger, older fish are taken in deeper water, and occurrences inshore and at depths less than 50 fm are usually associated with the presence of deep trenches over 50 fm.

The activity of lactate dehydrogenase was measured in the livers of 36 species of fish. These species could be divided into two groups, those with liver activities of more than 1000 mU/mg protein and those with activities of less than 100 mU/ mg protein. The lactate and pyruvate of samples of blood, muscle and liver from cod, plaice, bass and mackerel were determined. Samples were taken from ‘rested’ and trawled fish and from fish allowed to recover for 3 h after trawling. The rate of removal of lactate from the white muscle after capture in the trawl was not related to high blood and liver activities of lactate dehydrogenase. There was no relationship between the activities of nine of the glycolytic enzymes in the white muscle of cod and plaice and the liver lactate dehydrogenase activity. Little blood lactate appears to be taken up by the liver. It is concluded that the liver of cod, plaice and bass has a negligible role in metabolizing blood lactate.

The absorption of zinc has been studied in the brown seaweed Laminaria digitata (Huds.) Lamour., with use of the radionuclide 65Zn and atomic absorption analysis. No evidence of the regulation of zinc by the plant has been found. Absorption of zinc or 65Zn is a gradual process of accumulation which may continue throughout the life of the plant and is not accompanied by the exchange of zinc. As a result, once it has been absorbed, zinc or 65Zn shows little tendency to be lost from the plant. The amounts of zinc or 65Zn which can be accumulated from sea water containing different concentrations of zinc and the effects on these of growth, light and competition from other metals have been studied. Possible sites at which zinc might be bound have been discussed, and the experimental results have been compared with the situation found in the field.

The flash-stimulated luminescent response (FSLR) of euphausiids is a useful tool for the investigation of their bioluminescent behaviour. This paper describes the investigation of the effects of temperature upon a series of such FSLRs produced in individuals of Thysanoessa raschi (M. Sars) by three stimulations with an electronic photofiash at 20 min intervals. The following parameters of the response were measured: responsedelay, responseduration, the sum of these two {delay + duration) and the proportion of stimulations which produced a response. Initial experiments showed that all response delays were significantly different at 10°C and at 5°C, while second andthird response delays were not different from each other. The effect of a range of temperatures from 0° to 20°C on FSLR delay and duration is described. Regression lines based on the Arrhenius equation were fitted to the results. These showed that all response parameters decreased with increasing temperature, although Q10 varied from — 7.8 in the case of thefirst response delay to — 1.3 in the case of second/third response delay. This difference was the most marked effect of the second stimulation; the third stimulation caused no additional change. Below 10°C the second delay was shorter than the first delay. The independent response parameters were found to be delay and delay + duration. Duration resulted from the interaction of these two. These results are discussed and compared with the interpretation of the results of similar experiments by Kay (1965, 1966) onMeganyctiphanes norvegica.