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 superficial red muscle fibres of gnathostome fishes run more or less longitudinally, but the deeper muscle fibres are arranged in complex three-dimensional patterns in which some of them make angles of 30° or more with the long axis of the fish. There are two basic patterns, of which one is found in all the myomeres of selachians, primitive bony fishes, Anguilla and Salmo. In the other teleosts which were examined this pattern is restricted to the last few myomeres, and a quite different pattern is found more anteriorly.

In a fish with muscle fibres running longitudinally the lateral fibres would be able to contract far more than those near the vertebral column. However, from mathematical analyses included in this paper it appears that both the patterns which have been found should result in all the white fibres in a myomere contracting to a fairly similar extent when the fish bends. This seems likely to be advantageous because a muscle fibre of given intrinsic speed produces maximum power output at one particular rate of contraction.

A given rate of contraction of the muscle fibres results in faster bending if the fibres are arranged in the typical teleost pattern than if they are arranged in the selachian pattern.

The selachian pattern is probably retained in the caudal peduncles of teleosts because the faster bending is obtained only at the expense of weaker bending moments. The caudal peduncle is slender and would be less able to transmit large forces to the caudal fin if the teleost pattern of muscle fibres were continued to its posterior end.

After initial trials a technique was devised which made it possible to rear about 12 % of newly hatched larvae of the pilchard Sardina pilchardus (Walbaum) to a point well beyond the yolk-sac stage. A survival rate of this order was considered quite satisfactory for larvae which are so small at hatching.

The leopard-spotted goby, Gobius forsteri Corbin 1958, described from the western English Channel, is identified with the Madeiran Gobius ephippiatus Lowe 1839, the latter name becoming a senior subjective synonym for this species. From study of variation, with size of fish, in number of lateral-line sensory papillae in preopercular-mandibular row i, it is concluded that the Aegean Gobius thori De Buen 1928 may also be referred to G. ephippiatus. Examination of the syntypes of G. macrolepis Kolombatovic 1891, from the Adriatic, has shown that this name belongs to a close relative of G. ephippiatus and not to Mediterranean populations of the Atlantic Lesueurigobius friesii (Malm), as recent authors have supposed. A new genus, Thorogobius, is proposed for G. ephippiatus, the type species, and G. macrolepis, and a key provided to these two species, which differ in meristic features, development of pelvic anterior membrane and disc, head coloration, and relative number of sensory papillae. Further systematic data on material studied, synonymies, body proportions, papillae and meristic counts are also given.

As the complete list of known occurrences indicates, T. ephippiatus appears to be a warm temperate Mediterranean-Atlantic form which penetrates the eastern Atlantic boreal region around the British Isles at least as far north as the North Channel and eastwards to Lulworth Cove (western English Channel). As an inshore shelf species, T. ephippiatus occurs in or near crevices associated with vertical rock faces, from LWST to 30–40 m. Diet probably consists chiefly of crustaceans and polychaetes. Maximum total length recorded is 129 mm, and greatest age 9 years (determined from otoliths), with sexual maturity by the fifth year of life (age 4 +).

Two hydrographic cruises have been carried out in the Irish Sea during the winters of 1965 and 1966. It has been found that near the Welsh Coast reactive silicate concentrations were remarkably constant and lower than expected. In contrast, near the Irish coast there were marked variations in reactive silicate concentrations and the values found were considerably higher than those for the Welsh coast.

Experiments were carried out to assess the importance of desiccation during tidal exposure upon the vertical distribution of the intertidal limpets Patella aspera and P. vulgat vulgata. The rate at which water is lost during desiccation varies inversely with body size.

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 relationship between the calcite skeleton and associated cells in the spines of Echinus esculentus is described. The cell bodies lie in channels within the skeleton and cytoplasmic processes extend from them toward the calcite. Swollen regions of the cytoplasmic processes contain organelles such as mitochondria and various vesicles. The plasma membranes of the cytoplasmic processes appear to spread over the calcite surface which is thus topologically intracellular. A considerable portion of the stereom space is extracellular and contains an extracellular fluid and collagen fibres.

On the basis of extensive material from Plymouth an attempt has been made to determine the specific limits of the European species of the eolid genus Eubranchus Forbes. From a study of the living animals, jaws, radulae and reproductive systems, it is concluded that five species can be recognized as occurring commonly in Britain, Eubranchus tricolor Forbes (=Galvina viridula Bergh), E. farrani (Alder & Hancock), E. pallidus (Alder & Hancock), E. cingulatus (Alder & Hancock) and E. exiguus (Alder & Hancock). These species are all variable in coloration, but they can nevertheless be easily distinguished by coloration as well as by morphological and ecological characteristics. A further species, E. doriae (Trinchese) from the Mediterranean, was also examined and appears to be distinct. No material of Eubranchus rupiurn (Moller) and E. vittatus (Alder & Hancock) was available for examination, but these are provisionally maintained as distinct species. The European species of Eubranchus are compared with species from other parts of the world in an attempt to decide how many genera should be recognized. It is concluded that the armature of the penis and the liver branching do not form good generic characters, and that consequently Capellinia is to be regarded as a junior synonym of Eubranchus.

The numbers of young fish, excluding clupeids, taken in a 2 m ring trawl in the plankton off Plymouth were as high in the year 1966 as they were during the 1920s and early 1930s. There is thus evidence that the period of decreased abundance which began after 1934 and has apparently persisted since then may have ended. The year 1966 was a very early year for spring spawners and this can be correlated with the high water temperatures prevailing in the early months of that year.

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.

Methods of filtration and storage of sea-water samples intended for silicate analysis have been investigated. The desirability in some circumstances of filtering water samples before analysis has been demonstrated. The behaviour of three recommended methods for the analysis of silicate in sea water has been compared by inter-calibration studies.

Results of quantitative surveys of the polychaete fauna of certain fine deposits within Plymouth Sound, comprising a total of forty-eight species, are presented. The juvenile stages of certain species are described and sixteen species that have not been found previously in the area are recorded.

The density of 18 species, measured by weighing them in sea water and in air, was found to vary widely. The weights of these fish in sea water ranged from about 7 % to less than 1 % of their air weights.

Details are given of the nets used and the sampling procedures adopted to investigate patterns of vertical distribution in an oceanic pelagic fauna. Ancillary gear and laboratory methods are described. The paper concludes with a discussion of the limitations of the sampling.

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.

Studies made on the cod of the Barents Sea showed that in the adult female fish there were regular seasonal variations in the level of calcium and vitamin A aldehydes in the blood (Plack & Woodhead, 1966: Woodhead, 1968). These changes were directly related to each other (Woodhead & Plack, 1968) and it was suggested that the changes of both blood constituents might be influenced by oestrogen secretions from the ripening ovary. It has now been confirmed that oestradiol treatment increases the level of vitamin A1 aldehyde in immature cod (Plack & Pritchard, 1968), and the present paper describes the effect of oestrogen treatment on the concentration of calcium in the plasma, also relating this to vitamin A aldehyde changes.

The mean weight in sea water of specimens of the electric ray, Torpedo nobiliana Bonaarte, was only 0·4 % of the weight in air compared with 4·4 % in other bottom-living rays. T. nobiliana was so buoyant because it had large livers (up to 20% by weight) containing a lot (up to 70 %) of oil of low density (0·91 g/cm3) and because some of the body tissues were less dense than in other rays.

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.

The settlement behaviour of the larvae of Ostrea edulis has been examined in the laboratory. Preliminary experiments indicated that high light intensities (1250 lux) and food-cell concentrations (100,000 cells/larva) stimulated settlement, but varying the temperatures within the range 19–23 °C had little effect.