Recent improvements in gear and techniques have permitted much more detailed studies to be made of vertical distribution patterns of pelagic oceanic organisms (Vinogradov, 1970; Foxton, 1972). One such development is the RMT 1 + 8 opening-closing net system for sampling plankton and micronekton (Baker, Clarke & Harris, 1973) which can be acoustically monitored in situ for fishing depth, water temperature, flow and net operations. This sampler has been used to study the midwater communities in the N.E. Atlantic over the last 6 years during cruises by RRS ‘Discovery’. It has been successfully operated to depths of 4000 m.

The diatom Ditylum brightwelli requires, for vigorous growth in artificial sea water, two organic substances, or groups of substances, in addition to inorganic salts. The substances, or groups, act in a manner complementary to each other.

The effect of adding either is greatly increased by the presence of the other.

One accessory substance, or group, has been obtained in impure state from natural sea water and from extracts of algae by adsorption on carbon and elution. It has properties of an inorganic acid or internal anhydride.

The method by which the weight, volume, density and sinking factor of living aquatic organisms can be determined has been extended. By sinking factor is meant the ratio of the density of the organism to that of its environment at the time of the actual determination. The density of the environment is always raised to 1000, and the density of the organisms computed on this basis.

A quick and accurate method for determining the percentage of water in a living organism has been described and discussed.

On the assumption that a sponge consists of protoplasm and spicules only, the density of the protoplasm has been computed.

The sinking factor of several fish and of the embryos of some Crustacea at different stages has been determined. One effect of the swim-bladder in teleost fishes is to reduce the sinking factor and thus facilitate swimming.

The effect of the sinking factor on swimming in general and the effects of spinous outgrowths in pelagic Crustacea are discussed.

The principles and aims of numerical taxonomy were clearly stated by Sokal & Sneath (1963) and their procedures have since been adopted by many botanists working with numerous different groups of plants. Marine algal taxonomists, however, seem largely to have ignored these developments although Whitton (1969) has recommended that numerical techniques should be employed to help solve outstanding problems in the taxonomy of the Cyanophyta.

The ultrastructure, histochemistry and X-ray microanalysis of the metal-containing blood cells in three species of oyster, Ostrea edulis, Ostrea angasi and Crassostrea gigas are described. Granular cells containing both copper (up to 400 mM) and zinc (up to 1 M) are present in all three species. In addition,Ostrea edulis has two other granular amoebocyte types which specifically accumulate either copper (400 mM) or zinc (12 M). In all types of amoebocyte, the metals are stored in membrane-limited vesicles. The ultrastructure and histochemical staining characteristics of the vesicular contents vary according to metal composition. Zinc-containing granules appear basophilic after sulphide treatment and display homogeneous electron density; copper/zinc-containing granules are less dense and show varying degrees of crystallinity; copper-containing granules appear crystalline (however, any acidophilic or basophilic reaction is masked by the dark brown precipitate of copper sulphide).

Specimens of the onychoteuthid squid Moroteuthis ingens were collected from four sites in the Southern Ocean: Macquarie Island, the Falkland Islands, the Chatham Rise (New Zealand) and the Campbell Plateau (New Zealand). Spatial variations in diet among these areas were investigated using stomach contents and lipid and fatty acid profiles. Myctophid fish were prominent prey items at all sites, and the diet at New Zealand sites contained temperate myctophid species that were not identified at other sites. The diet at the Falkland Islands differed considerably from other sites due to the large proportion of cephalopod prey that had been consumed by M. ingens. This is likely to be due to the absence of key myctophids, such as Electrona carlsbergi, and the abundance of smaller squid such as Loligo gahi and juvenile M. ingens over the Patagonian Shelf. Stomach contents data could not be used effectively to determine dietary differences between the Chatham Rise and Campbell Plateau, largely due to differences in sample sizes between these sites. Lipid class and fatty acid profiles of the digestive gland indicated that the diet of M. ingens differed significantly between the Chatham Rise and Campbell Plateau, despite the relative proximity of these sites. We conclude from total lipid content that this was due to a reduction in food availability to M. ingens at the Campbell Plateau. The highly productive waters of the Subtropical Front pass over the Chatham Rise, whereas the Campbell Plateau is situated in less productive sub-Antarctic water. Differences in oceanographic conditions are likely to have driven dietary variations between these two sites.

1. Ligia is a nocturnal animal inhabiting crevices in rocks above high-tide level. It is omnivorous though Fucus spp. form the main article of diet.

2. Immersion experiments were carried out in which the animals were subjected to a gradual transition from salt to fresh water. None survived this treatment for more than one month. It was noticed that the reduction in salinity was accompanied by an increase in the rate of beat of the pleopods.

3. Animals were subjected to sudden and gradual changes in temperature. One specimen survived a change from water at 15° C. to water at 30° C. for 28 minutes, but was dead after 78 minutes; a second, changed from water at 15° C. to water at 35° C, was to all appearances dead after 8 minutes, but recovered after being replaced in water at the original temperature.

The ability of the slipper limpet Crepidula fornicata L. to feed on suspended particles carried into the mantle cavity by cilia on the gill has attracted attention for many years since the feeding mechanism was described by Orton (1912). Subsequent studies were made on the possible origins of this mode of feeding (Yonge, 1928, 1938), and later Werner (1951, 1952, 1953, 1955, 1959) made more detailed observations on the mechanisms by which particles are retained by the animal. He showed that coarse particles are strained by means of a mucus filter covering the inhalant aperture to the mantle cavity, whilst the majority of the medium and fine particles are entangled by a second mucus filter secreted by an endostyle and which lies against the frontal surface of the gill (for review, see Jørgensen, 1966; Newell, 1970).

The Ostreidae are well known for their high intra-specific variation, which makes identification problematic. The present paper aims to provide a morpho-anatomical and taxonomic review of the Brazilian species of Crassostrea, as well as some congeneric species from other relevant areas. The Brazilian species are Crassostrea mangle sp.nov. and Crassostrea brasiliana. The exotic species Crassostrea gigas, cultivated in the southern region of the country, is also included in this study. Additional species are: Crassostrea virginica, from the Atlantic coast of the USA, the type species, and Crassostrea rhizophorae, a south-eastern Caribbean species that is supposed to occur in Brazil, but is here understood as a different entity endemic to that region. Taking into account their economic importance, the differentiation between these species is critical, and is essential for a better planning of production and preservation strategies. We point out the differences in almost all structures amongst these species, which are formally redescribed herein. The occurrence of the African species Crassostrea gasar in Brazil is established as false. The voucher specimens of previous studies responsible for this assumption were examined, evidencing a misidentification for Crassostrea brasiliana from an estuarine environment. The geographical distribution of the studied species is recognized as follows: Crassostrea rhizophorae in the south-east Caribbean Sea; Crassostrea mangle sp. nov. from Pará to the Santa Catarina, only in mangroves; Crassostrea brasiliana from Paraíba to Santa Catarina, both in rocky shores and mangroves; Crassostrea virginica ranges from the Atlantic coast of Canada to the Caribbean; and Crassostrea gigas originates from the Indo-Pacific, but has been introduced in southern Brazil. This paper also deals with conchological aspects of the endemic species Crassostrea praia, from south Lagoa dos Patos, Rio Grande do Sul; after a more detailed definition, and considering the deleterious effects of the nearby port and construction sites, it can be classified as an endangered species.

The epibiotic communities on locally abundant macroinvertebrates, in particular the brachiopod Liothyrella uva and the limpet Nacella concinna, were examined from depths between 0 and 50 m at Signy Island, Antarctica. The percentage cover by epibionts on Liothyrella increased from <20% on the smallest individuals to >50% on the largest, and decreased slightly with depth. The percentage cover of Nacella by epibionts increased with size of individual over an approximately similar range of values, but in contrast with Liothyrella increased greatly with depth. Cheilostome bryozoans and annelids of the genus Spirorbis formed >90% (by area) of the colonists on Liothyrella and 30–60% on Nacella, the coralline alga Lithothamnion and sponges making up the remainder. The bryozoans, which generally dominated the epibiotic communities, comprised complex associations of species which could be described as either generalists, host-specific epibiotic, low specificity epibiotic or locally abundant background species. Positive associations of both occurrence and abundance were found between some of the bryozoans living epibiotically on the brachiopod Liothyrella. The overgrowth interactions recorded, between the three main epibiotic faunal taxa; sponges, bryozoans and annelids, were essentially hierarchical. Sponges usually overgrew Bryozoa, and Bryozoa overgrew Spirorbis as well as occasion-ally smothering small brachiopods. In four adult Liothyrella death may have been caused by the epibiotic bryozoan Arachnopusia inchoata growing over the gape, so preventing feeding and/or respiration.

In a benthic mesocosm experiment, the effects of two species of burrowing Thalassinidean shrimps (Callianassa subterranea and Upogebia deltaura) on rates of sediment denitrification were determined using the isotope pairing technique. Denitrification rate (Dtot) and coupled nitrification–denitrification (Dn) were shown to be significantly enhanced by the presence of U. deltaura by 2·9 and 3·3 times respectively, relative to control measurements. For U. deltaura the stimulation of the denitrification rate was found to be significantly related to the size of the animal (F=5·81, P=0·042). No deviation from the rates determined in control cores for either Dtot or Dn was observed for those cores inhabited by C. subterranea. The increase in Dtot with U. deltaura was considered to be the result of a combination of different factors, including; the direct extension of the sediment–water interface and an increase in oxygenation of the sediments and solute transport, as a result of the ventilating activities of the animal itself.

Numerous studies have shown that only a small percentage of the organic carbon produced by photosynthesis in the upper layers of the oceans reaches the underlying sediments (see review by Angel, 1984). During intense phytoplankton blooms, plant cells could account for most of the organic carbon contributed to sediments in certain shallow inshore areas (Smetacek, 1980). Examination of the sediments from open ocean environments, however, indicates that the main contribution of organic carbon to these is in the form of faecal material released by zooplankton, for example salps (Iseki, 1981) and larger species of copepod (Schrader, 1971; Krause, 1981).

Effects of water of reduced salinity on the vertical migration of the zooplankton of Southampton Water were investigated in the laboratory using the adults of six copepod species (Acartia tonsa, A. bifilosa, A. discaudata, A. clausi, Centropages hamatus, Temora longicornis) and the larvae of one decapod species (Porcellana longicornis). Additional observations were made on Centropages typicus adults taken off Plymouth.

Salinity discontinuity layers had a marked effect on the vertical migration of zooplankton. A single discontinuity layer formed by placing less dense diluted sea water over full strength sea water acted as a barrier to animals attempting to swim toward the surface of an experimental water column and no individuals were able to enter the zone of reduced salinity when an extreme dilution was used. Comparison of the behaviour of various species and of different sexes or developmental stages of a particular species suggests that vertical distribution was partly dependent on the salinity tolerances of individuals. Upward migration was also restricted by a vertical series of discontinuity layers.

The swimming activity of copepods was depressed in homogeneous water columns of reduced salinity. Activity depended both on the degree of dilution and on the period of immersion. There were indications that behaviour varied according to the salinity tolerances of the different species.

Adults of the isopod Paragnathia formica inhabit burrows in saltmarsh banks from which they release larvae during autumn high tides. Larvae pass through three moult stages, each of which feeds ectoparasitically on estuarine fish (including Pomatoschistus microps), before a final moult to a non-feeding adult stage. The entire energetic reserves for survival and reproduction up to nine months (females) or 16 months (males) later are therefore acquired during these three brief periods of parasitism. Application of a plankton sampling technique showed larval density in the water to vary considerably between successive high tides. High densities of larvae (1 per 1·2 l) occurred on only one tide during a week-long study, when a corresponding peak in parasite prevalence in the fish population (10%) was recorded. Peak larval release was observed as the tide rose, at a time when host fish have been reported to be in greatest abundance. Considerable larval longevity was demonstrated in the laboratory in the absence of food (mean=43 d). Data are interpreted, in conjunction with field observations, in relation to larval parasitism opportunities post-birth.

Tumtella communis is a highly specialized burrower in gravelly mud. Once buried, it moves little in correlation with its apparently exclusively ciliary feeding habit. An inhalant depression in the mud is made by lateral movements of the foot. There is a unique exhalant siphon constituted by two overlapping folds, and through this water and faecal pellets are expelled without disturbing the surrounding mud.

INTRODUCTION

Ascidian tadpoles are short-lived, actively swimming larvae. On attachment to their preferred substrates they absorb the tail, and with it all their locomotory equipment. The behaviour is in general geared to the short-term problems of dispersion and settlement (Crisp & Ghobashy, 1971).

The small size of these tadpoles (2 mm in Dendrodoa grossularia, van Beneden, the species used) makes them difficult to handle. Surgical operations on the nervous system (Kasas, 1940), such as we were able to perform on the tadpole-like but larger Oikopleura (Bone & Mackie, 1975) are scarcely feasible here. Nevertheless, it is desirable to know more about the tadpoles’ locomotory organization if only because their possession of the chordate type of locomotory equipment raises interesting questions concerning possible functional parallels and evolutionary origins.

The taxonomic position of the golden-brown flagellate Diacronema vlkianum Prauser has hitherto been uncertain. It was first reported by Vlk (1938) from fresh water and a brief description given, particular interest being ascribed to the flagella which staining and light microscopy indicated to be without appendages. Because of this Vlk concluded that the organism, which he did not name, occupied a taxonomic niche somewhat apart from typical chrysophytes. In 1958, Prauser isolated, also from fresh water, a flagellate which he identified as Vlk's organism and he described it using both electron microscopy of shadow-cast cells and optical microscopy of living material. He confirmed the lack of flagellar hairs and discussed the taxonomy of Diacronema in relation to both the Ochromonadales with heterokont flagella and the genus Chrysochromulina Lackey with equal smooth flagella. He suggested that the genus could be thought of as representing a new family, the Diacronemataceae, arising from an ochromonad stock and possibly representing a unique line within the chrysomonads.

Glass eels of the American eel Anguilla rostrata (Lesueur) utilize selective tidal stream transport, a series of semidiurnal vertical migrations in phase with the tide, to migrate up the Penobscot River estuary, Maine, U.S.A., in the spring. Glass eels, freshly collected during their migration, exhibited rhythmic activity with circatidal periodicities when tested in groups in the presence of a water current under constant conditions in the laboratory. Freshly collected groups of eels which had already completed their migration through tidal water did not exhibit circatidal activity rhythms under the same conditions. The activity rhythms of groups of eels freshly caught in tidal water appeared to be entrained by a 12.5 h cycle of water current reversals, but not by a 10.0 h cycle of current reversals. In other entrainment experiments water collected on flood and ebb tides was alternately added to the experimental tanks every 5.0 h. Under these conditions groups of eels freshly caught in tidal water did not display any rhythmic activity. Only 2 of 100 glass eels, freshly collected from tidal and non-tidal water, which were tested individually in static tanks, exhibited rhythmic activity. The activity rhythms would allow an eel to time its vertical migrations in the estuary despite varying environmental conditions.

1. A study of the adult population of Sagitta elegans Verrill has been made in the waters off Plymouth by weekly collections with the 2-metre stramin ring-trawl hauled obliquely in the daylight.

2. Measurements of large samples and a study of the state of development of the gonads has shown that there were apparently four, if not live, broods of S. elegans produced in the year.

3. These successive broods were apparently spawning in April-May, June-July, and September, 1930, and February, 1931.

4. In the offspring of the September spawning population no gonads were developed during October and November. The male organs started to ripen in December, and the ovaries in January, but the brood did not appear to be fully mature until February.

Adult and larval stages of Siboglinum fiordicum, collected from 32 to 35 m depth, accumulate measurable quantities of amino acids and glucose from low concentrations. The amino acids are absorbed against a considerable gradient. The glucose and the amino acids are metabolized in the tissues and substantial amounts are respired to give carbon dioxide or volatile organic acids. Under the experimental conditions almost all the metabolism follows aerobic pathways.