Two samples of Neanthes succinea (Frey & Leuckart 1847) from the Mediterranean Sea were investigated. Twenty-one loci were analysed; seven of them were polymorphic in both populations. The level of heterozygosity was 2.2% and 4.4% in populations from the Tyrrhenian and Adriatic coasts respectively. The value of Nei's genetic identity index (1=0.965), together with the mean F(IT) (=0.350), shows that the samples can be considered reproductively isolated populations. F-statistics indicate that ME-1 is the discriminant locus between populations.

Oceanic and coastal bioluminescence in surface waters, in many instances, is produced by microscopic dinoflagellates. Their light emission is usually observed at a maximum during the night hours and markedly inhibited during the day. This diel periodicity has never been observed in situ for identified species and never before in heterotrophic Protoperidinium dinoflagellates. Pronounced differences in stimulable bioluminescence measured with bathyphotometers in Vestfjord, Norway in September 1990 correlated with simultaneous ship-board laboratory experiments. Cells of both the photosynthetic Ceratium fusus and heterotrophic Protoperidinium curtipes showed a pronounced inhibition of bioluminescence during the day and maximum bioluminescence at night.

Age and growth were estimated in the European squid, Loligo vulgaris, by examining growth increments in the statoliths of 203 specimens collected from off the French Mediterranean coast. Length and increment data were analyzed assuming that the increments were formed daily. The relationships between age and length showed that: growth rate varied considerably among individuals; growth was double exponential; the squids grew on average to 240 mm ML at 240 d from hatching, with a maximum of 350 mm at 240 d; the life span is probably about one year.

Research ships are much more numerous on the high seas in the 1990s than they were in the 1950s. At that time the United Kingdom was fortunate in that it had a purpose-built research vessel, RRS 'Discovery II' (see inside back cover), the successor to Scott's 'Discovery' (which was itself granted the title Royal Research Ship in 1923, see inside front cover). 'Discovery II's prime objectives had originally been oceanographic research in the Antarctic relevant to the whaling industry, to which end she had completed six two-year Antarctic commissions. In the 1950s she was being operated by the National Institute of Oceanography and was working extensively in the North Atlantic, covering the gamut of marine physics, chemistry, biology and geology, including participation in the research programme of the International Geophysical Year. However, by 1959 she was 30 years old, and both scientific space and stability had become limiting. Increasingly stringent Ministry of Trade requirements were also making successive refits less and less cost-effective. In April of that year the first brief outline for a replacement vessel was prepared, and six months later discussions between naval architects and the National Oceanographic Council (represented by Dr H.F.P. Herdman) produced an outline draft specification for the new ship. Further discussions with the Admiralty finally resulted, in June 1961, in an order being placed for a new vessel, at an estimated cost of £800K (Deacon, 1967).

The new ship, the RRS 'Discovery', was launched in July 1962 and commissioned on 17 December, 10 m shorter than her originally conceived length but at a contained final cost of £802K.

This paper reports the results of experiments designed to investigate the relationship between thermal stability of DNA and the physical and chemical conditions experienced by various species of invertebrates, with particular reference to hydrothermal vent organisms. The major conclusion is that thermal stability correlates positively with environmental temperature within the DNA regions encoding ribosomal RNA, but not throughout the genome. Increased thermal stability (based it is supposed on an increase in G-C content) of rDNA relative to total DNA confers protection to coding sequences which would otherwise be susceptible to damage during transcription. An increase in G-C content of rDNA will lead to an increase in G-C levels in rRNA which forms a major structural component of ribosomes, thus conferring increased thermal and chemical stability to these sites of amino acid synthesis within the cell.

Samples of female lllex argentinus were taken from the catch of a Japanese squid jigging vessel on the Patagonian Shelf during March 1986. Morphometrics of the somatic and reproductive organ systems and the histological structure of the mantle in relation to maturation were examined. The data suggest that growth and maturation occur simultaneously during most of the time that lllex argentinus females are on the feeding grounds. In a squid of a ‘standard’ mantle length the whole body mass increases relative to mantle length during maturation and growth of the reproductive organs. This is accompanied by a small but significant decrease in the relative mass of the mantle, head and viscera whilst the mass of the digestive gland remains constant. Although mantle mass of a ‘standard’ female squid decreases relative to mantle length with maturity this is not associated with degeneration of the mantle muscles. Energy and nutrient resources for maturation are apparently derived from the squid's food, not from reserves, and during the course of maturation there is an increasing shift of emphasis from somatic growth to production of gonad and accessory reproductive organs.

The aspidochirote Holothuria forskali is a large common species found in the Atlantic and the Mediterranean. Its reproductive cycle has been determined in a population from Brittany using histological observations of the different classes of gonadal tubules, oocyte size frequencies and evolution of gonad indices. The cycle is annual and synchronous in both sexes. The different phases are well marked and are characterized by a long maturation during summer and autumn followed by a pre-spawning period during winter. Spawning is probably related to the increase in temperature. Most of the mature gametes are released. The resorption of the relict and spent tubules continues during the onset of the next vitellogenesis in the secondary tubules, without a rest period. The reproductive effort, documented from the gonad indices, is very high in this population which is composed of adult individuals.

Three latitudinally separated assemblages (49°–41°N, 38°–30°N, 22°–20°N in 11°–25°W) of abyssal demersal fishes in the eastern North Atlantic have been identified from combined data from 13 new and 12 previously reported trawl samples. The northerly assemblage remained unaltered by the new data, but the intermediate one could be sub-divided into shallow (4370–4475 m) and deep (4835–5440 m) elements. This sub-division revealed that bathymetry was acting with latitude to influence previous results. The new, southerly, assemblage was found below surface waters enriched by upwelling along the continental margin. The composition of dominant species identified each assemblage. The biological characteristics of these species were largely consistent with the former hypothesis linking them to the influence of the overlying production regime. The contrast between this preliminary evidence for structured demersal fish assemblages in the abyss with its lack on the slope and rise was discussed in the terms of the respective patterns of trophic input.

‘Four-winged’ flying fish (in which both pectoral and pelvic fins are hypertrophied) reach greater maximum sizes than ‘two-winged’ forms in which only the pectoral fins are enlarged. Exocoetus obtusirostris shows negatively allometric growth in relation to standard length in terms of body mass (b=2·981), and lateral fin area (b=1·834). In consequence, wing-loading rises in positive allometric fashion with standard length (b=l·236). Pectoral fin length cannot be greater than 78–79% of standard length or swimming will be impaired, so the requirement for increased flying speed resulting from increased wing-loading during growth means that lift:drag ratios have to be improved by relatively narrowed wings and tapered wing tips; features which in turn increase wing-loading. Evidence is presented to show that hypertrophied pelvic fins in four-wingers are required to solve problems of stability in pitch, rather than to decrease wing-loading. The ‘non-flying’ flying fish, Oxyporhamphus micropterus, has very high wing-loadings, but the main reason that it cannot fly is that the centre of gravity of the fish is so far behind the pectoral fins that stalling on take-off would be inevitable. Flying fish possess reasonable quantities of red axial musculature, but no more than are used for cruising in fast-moving pelagic fish such as mackerel; it seems probable that acceleration to take-off speed in flying fish requires use of anaerobic white muscles.

Comparative ultrastructural features of the ovary and vitellogenesis have been described for six shallow water and four bathyal species of sea cucumbers representing four major holothuroid orders. Ovarian structure is similar in all ten species except for features of the peritoneal cells of the outer layer and the follicular inner epithelial cells surrounding the developing oocytes. The peritoneal cells vary from monociliated squamous or cuboidal cells to large columnar cells. Ultrastructural evidence suggests that these cells might be capable of incorporating materials from the perivisceral coelom. The follicular inner epithelial cells of two deep-sea species resemble podocytes, a feature previously unre-ported in holothuroid ovaries. It is suggested that these cells function to increase nutrient exchange between the genital haemal sinus and the oocyte during vitellogenesis. In all ten species, the oocytes appear to participate in yolk synthesis through the interaction of the Golgi complex and rough endoplasmic reticulum. The similarity in the ultrastructural features of vitellogenesis suggests that the process of yolk synthesis has been highly conserved in holothuroids. Endocytotic activity was detected in seven of ten species but it is uncertain if this is directly related to vitellogenesis. Cilia and intracellular structures resembling striated ciliary rootlets were observed in the oocytes of four of the ten species studied. The significance of this finding is unclear but could indicate that germ cells have a somatic cell origin.

Samples of male Illex argentinus were taken from the catch of a Japanese squid jigging vessel on the Patagonian Shelf during March 1986 and an analysis was carried out on the morphometrics of the somatic and reproductive organ systems in relation to maturation. The data show that growth and maturation occurred simultaneously during most of the time that Illex argentinus males were on the feeding grounds over the southern Patagonian Shelf. In a squid of a ‘standard’ mantle length the whole body mass increased relative to mantle length during maturation and this could be attributed to the increase in mass of the reproductive and accessory reproductive organs. During maturation the mantle and digestive gland mass showed no significant change relative to mantle length. The mass of the head increased and the mass of the viscera decreased relative to mantle length. In male Illex argentinus, as in the female, the energy and nutrient resources for maturation are derived from the squid's food and during the course of maturation there is an increasing shift of emphasis from somatic growth to production of gonad and accessory reproductive organs. The proportional investment of body mass in reproductive and accessory reproductive organs predicted for a fully mature male Illex argentinus was less than half that of the female.

The presence of antibacterial activity in the haemocytes of the shore crab, Carcinus maenas (L.) (Crustacea: Decapoda), was investigated using a selection of Gram-positive and Gram-negative bacteria from geographically diverse waters. Preliminary investigations into the relationship between this activity and the prophenoloxidase activating system (proPO) were also carried out. Antibacterial activity against both Gram-positive and Gram-negative organisms were found to reside exclusively in the granular haemocytes and eight of the twelve bacteria tested were susceptible to this effect. Additional studies, using Psychrobacter immobilis (= Moraxella sp.), revealed that the factor (or factors) responsible was 90% effective within 60 min and was also heat stable, independent of divalent cations, and non-lytic in character. Although antibacterial activity resides in the same cell population that carries the proPO system, there appears to be no relationship between antibacterial activity and phenoloxidase itself. Other components of the proPO system, however, may be involved.

Some of the limits to the use of serology to identify prey species in the digestive tracts of cephalopods have been evaluated. Cuttlefish, Sepia officinalis, were given meals of krill slurry (Euphausia superba). Protein extracts of contents from four regions of the digestive tract, stomach, caecum, digestive gland and intestine, were tested for prey antigenicity. Digestion times (loss of antigenicity) ranged from 1 to 8 h depending on sampling site. Stomach and caecum emptied rapidly, but meal antigenicity persisted longer in the digestive gland. The Sepia experiments provide a basis for interpretation of results from natural predation by cephalopods).

Video recordings were made of the behaviour of hyperiid amphipods and other mid-water crustaceans in a tank lit from above with a dim VDU screen, and from behind with infra-red light. Computer-generated stimuli could be moved across the VDU screen. Amphipods swam at speeds up to 19 body lengths per second. Some (Brachyscelus, Phrosina) consistently swam inverted, rolling from side to side. Others (Platyscelus, Parapronoe) spent periods of time rotating in the water with the dorsal acute zone of the eye pointing upwards. Both behaviours are interpreted as forms of visual scanning. Different species were active at different light levels, Phronima preferring the dimmest illumination. Three kinds of visual behaviour were seen consistently. The animals dropped from the surface as a dark square passed above them; they tracked other individuals (Hyperiids) or, in the case of Euphausiids, the stimuli on thescreen above; and they occasionally swam towards each other and collided, apparently deliberately.

The timing of spawning and recruitment in the squid Loligo forbesi in Scottish waters is described on the basis of data from three sources: monthly samples of squid caught by commercial trawls (1986–1988), egg masses found by fishermen (1987–1991), and statistical data on animals caught by research trawls (1978–1987).

Spawning females were present in samples from December to June, with peak spawning occurring in March. Most records of egg masses were from these months, but eggs were also found in August and September. These results suggest that there is an extended spawning season.

Small squid (≤100 mm dorsal mantle length) were rarely present in commercial samples, but were recorded in research samples almost all year round. Thus there appears to be more or less continuous recruitment into the catchable population.

The results of the present study are consistent with published data from other parts of the geographic range in that there is a regular seasonal peak in spawning, and spawning adults disappear from the population in summer. Further interpretation of the life-cycle of this species is not justified on the basis of current knowledge, and more information is needed on migrations, geographical variation, and lifespan in Loligo forbesi.

The development of the lecithotrophic encapsulated larva of the internally-fertilizing, sublittoral gastropod Turritella communis Risso 1826 was documented using scanning electron microscopy and light microscopy. Encapsulated development was completed in 12 days at 15°C in the laboratory. Spawning occurred above ~10°C. Spawn masses consisted of numerous gelatinous egg capsules, each of which contained ~28 eggs, encased in albumen and fertilizing sperm. The eggs had an average diameter of 139 μm. Fertilization was accomplished by unpaired eupyrene sperm and occurred at the germinal vesicle stage. The developmental sequence followed the typical gastropod pattern, but was unique in a number of respects. Polar lobes were produced during meiotic maturation and early cleavage, with an especially large lobe occurring in association with the first cleavage, which was unequal. The blastula developed into a dorso-ventrally flattened placula at the 70-cell stage. Gastrulation occurred through invagination and epiboly acting together, and was uniquely accompanied by the development of ectodermal microvilli measuring ~ 1 μm in length. Extra-embryonic albumen began to be depleted after the development of the microvilli. It is proposed that the ciliated telotrochal cells gave rise to the pair of statocysts. Torsion was additionally observed to be facilitated by the growth of pre-mantle tissue on the right side and retardation of growth on the left side.

The biology of young scallops Pecten maximus (Mollusca: Bivalvia) was examined using SCUBA diving. Within shallow and sheltered bays settlement took place near adult populations. Surfaces to which scallops attached were generally free of silt; these included algae, invertebrate tests and inorganic materials. Detachment could take place amongst individuals of 1 mm; however, in sheltered bays most remained attached until 4–13 mm. Following detachment scallops recessed in sediment. They were subject to dispersal by water turbulence and swimming induced by sea-stars. There was evidence to suggest high mortality from crab and sea-star predation during the summer and autumn.

A light and electron microscopic study of the enterocytes and gut-associated lymphoid tissue (G ALT) of the flounder Platichthys flesus showed regional differences in the structure of the epithelial cells. Epithelial villi decreased in height and spatial complexity, but increased in overall thickness in the posterior intestine. There were no specialized cells comparable with mammalian M cells. Periodic acid Schiff (PAS) activity increased in the enterocytes and goblet cells in the anterior intestine where alkaline phosphatase activity was most pronounced in enterocytes. Adjacent cells were joined by tight junctions.

Gut-associated lymphoid tissue was composed of isolated leucocytes in the epithelium and lamina propria with no accumulations. Numbers of intra-epithelial leucocytes were not statistically different in the various regions of the intestine. Five leucocyte types were distinguished among the gut-associated lymphoid tissue although lymphocytes and granulocytes were the most common. Granulocytes were positive for the Romanowsky stains with PAS/Alcian blue positive granules. Blast cells similar to large lymphocytes were unevenly distributed through the different regions of the intestine. Plasma cells were more numerous in the epithelium than in the lamina propria. Macrophages were rarely detected.

The anatomy of the eyes of several species of mesopelagic decapods (family Oplophoridae), obtained from the eastern north Atlantic, is described and related to the unique light environment of the deep seas. The oplophorid eyes are of the reflecting superposition type, but they show a number of regional morphological variations. The main rhabdom, formed by retinula cells Rl to R7, comes in a variety of shapes, from fusiform rhabdoms in the dorsal region of the eyes of Oplophorus spinosus to multi-lobed interdigitating rhabdoms in deepwater species. The distal rhabdom, contributed to each ommatidium by retinula cell R8, gradually increases in size towards the ventral part of the eye in Systellaspis debilis and O. spinosus. Histological examination of the tapetum shows that it is incomplete dorsally in some species from the upper mesopelagic zone (S. debilis, O. spinosus), and that the amount of reflecting pigment in the tapetal cells increases in the ventral part of the eye. The tapetum is complete in some deep-water species (Systellaspis cristata, Acanthephyra kingsleyi, A. pelagica). These adaptations of the rhabdoms and tapeta are thought to be concerned with increased sensitivity to the dim up-welling irradiance and to bioluminescence. A dorsal accessory compound eye consisting of a small group of apparently functional apposition-type ommatidia is described.

Nautilus can survive for long periods in water of very low oxygen content. Below a PO2 of around 25 mm Hg activity becomes intermittent, with brief periods of jet propulsion punctuating longer (typically 15–20 min) periods at rest. During these inactive periods ventilatory movements cease and the heartbeat slows to one or two cycles of very low amplitude per minute. The onset of an active period is heralded by an increase in heartbeat frequency and amplitude and a resumption of visible ventilatory movements. The large blood volume and very high oxygen affinity of the blood pigment apparently ensure that the animal accumulates sufficient oxygen during the resting intervals to fuel the brief active periods. Recovery, even after prolonged exposure to near anoxic conditions, is very rapid if the animal is exposed to well-aerated water. These capacities are not only related to a strategy of defence by withdrawal but would also allow Nautilus to exploit environments where the low oxygen content might limit competition from most fish and crustaceans. It is argued that a Nautilus-like physiology and behaviour could well have contributed to the success of extinct ectocochleate forms, living in oceans that were, by and large, less well oxygenated than now. The downward extension of oxygen-rich water and progressive elimination of hypoxic regions from the continental shelves during the Mesozoic may have contributed to the extinction of the ectocochleates by opening up the hitherto hypoxic environments, which they were adapted to exploit, to the more strictly aerobic high metabolic rate competitors and predators that eventually replaced them.