Marine organisms have long provided ideal systems for the study of development. The reasons for this are essentially twofold. Firstly, gametes, zygotes and embryos of many species are relatively accessible, facilitating observation and experimental manipulation. Secondly, the exceptional diversity to be found in the sea allows wide ranging comparative and evolutionary studies. The aim of this meeting was to highlight significant advances in developmental biology research using marine organisms and to bring together workers from a variety of disciplines to encourage cross-fertilization of ideas and comparisons between different systems. Particular attention was paid to new approaches for solving fundamental problems at different levels of complexity and organization. The meeting was organized such that parallel developmental processes in different systems, both animal and plant, could be compared. Sessions covered egg activation/cell cycle control; polarization/early development; embryogenesis/larval development; and the interaction between development and environment. Examples were chosen from a wide range of organisms, including molluscs, echinoderms, asddians, echiuran and polychaete worms, ctenophores, copepods, amphioxus, fish and algae (Brownlee, 1993).

It is generally agreed that fertilization in deuterostomes is accompanied by a large intracellular calcium wave that triggers the onset of development, but we still do not know exactly how the calcium wave is generated. The question has two parts: how does interaction of sperm and egg initiate the calcium wave, and how does the calcium wave spread across the cell? Two provisional answers are available to the first part of the question, one involving receptor-G-protein interactions of the sort that mediate trans-membrane signal transduction in somatic cells, the other injection of an activating messenger when sperm and egg fuse. Both these ideas are being actively pursued; the dialectic is productive, albeit no synthesis is in sight. We discuss their strengths and weaknesses. The second part of the question can now be much more precisely formulated: thanks to the recent flush of interest in calcium waves in somatic cells, new ideas and new experimental tools are available. The work on somatic cells repays a debt to eggs, where the basic properties of calcium waves were first set out, ten years before they turned up in somatic cells.

In the undisturbed sea urchin embryo, cleavage of the blastomeres is invariant and gives rise to five polyclonal territories that are each defined by the larval structures to which they give rise, and by unique programmes of gene expression. These territories are the aboral ectoderm, the oral ectoderm, the vegetal plate, the skeletogenic mesenchyme, and the small micromeres. Structural gene markers for four of these territories (all except the small micromeres, which participate in later development) have been cloned and characterized, and the regulatory domains of several of these genes have been mapped to the level of specific protein-binding sites.

The extracellular matrix of the sea urchin involves a protein with a molecular weight of 180 kDa (sea urchin fibronectin), which corresponds to mammalian fibronectin, and a nectin specific to Echinoidea with a molecular weight of 105–115 kDa (sea urchin nectin). Sea urchin fibronectin and sea urchin nectin have cell adhesion protein properties. They are, however, different from each other in biochemical properties, biological functions and intraembryonic distribution. Sea urchin fibronectin isolated from the sea urchin ovary accelerates scattering of micromere-derived cells and promotes spicule formation of micromeres in vitro. Sea urchin nectins identified so far in Paracentrotus lividus (Lamarck), Temnopleurus hardwicki (Gray) and Pseudocentrotus depressus (A. Agassiz) are presumably homologous molecules displayed in different species. They seem to be secreted into the hyaline layer as its constituents, and to play some role in morphogenesis of the embryo.

Ascidian development is reviewed and a model is presented for specification of the larval body plan and cell fate during embryogenesis. The model involves the combined activity of determinants inherited from the egg and inductive cell interactions in the embryo. It is suggested that there are four determinant systems in the egg which are segregated to different blastomeres during cleavage. The ectodermal, endodermal, and muscle determinants specify cell fate autonomously, while the axial determinants initiate cell-shape changes at gastrulation and generate a cascade of inductive activities establishing the larval body plan. In the proposed signalling cascade, the endoderm induces notochord by generating a planar inductive signal late during the cleavage phase, and the notochord cells in turn induce the nervous system by generating a vertical inductive signal in the overlying ectoderm during gastrulation. Ultraviolet (UV) irradiation experiments are described which suggest that axial and muscle determinants exhibit UV-sensitive components resembling nucleic acids and proteins, respectively. The model is evaluated in terms of developmental changes during the evolutionary transition from indirect to direct development. This transition can be explained according to the model by loss or inactivation of the muscle determinants and modification of the inductive activities generated by the axial determinants. These changes are supported by recent studies of embryogenesis in direct-developing ascidians.

The embryology of amphioxus (Chordata: Cephalochordata) has features in common with vertebrate embryology, reflecting a close phylogenetic relationship between the two taxa. Amphioxus differs from vertebrates, however, in having less complex organogenesis and cranial morphogenesis, and less specialization along the anteroposterior body axis. Here we illustrate this by describing the embryology of an amphioxus species, Branchiostoma floridae. To gain further insight into the origins, evolutionary divergence and comparative embryology of these taxa, we are comparing the molecular control of embryonic development in amphioxus and vertebrates. For these analyses, we are focusing on homeobox genes: a diverse multigene family implicated in developmental control in many Metazoa. We report the results of PCR-based experiments which reveal that the amphioxus genome has homeobox genes from several recognized gene classes. The PCR experiments also suggest that amphioxus has fewer ‘Hox’ and ‘Msx’ class homeobox genes than do vertebrates. We suggest, therefore, that amphioxus may be a living descendant from an intermediate stage in the evolution of homeobox gene family complexity, and the complexity of vertebrate developmental control. The pattern of gene expression during embryogenesis has been described for one amphioxus homeobox gene of the Hox class. This gene is primarily expressed in the presumptive neural tube of amphioxus neurulae, later embryos and larvae, in a spatially-restricted manner. The expression data lead us to suggest that Hox genes are involved in the control of spatial patterning in the neural tube of amphioxus; the data are also interpreted as giving insight into possible homology between the amphioxus and vertebrate body plans.

Studies of the larval nervous system of two species of starfish were carried out using antisera to a recently isolated native echinoderm neuropeptide, GFNSALMFamide (S1), and to serotonin. S1-like immunoreactivity was found in the larvae of the asteroids Pisaster ochraceus and Asterias rubens (Echinodermata: Asteroidea), originating in the apical region and becoming concentrated as two groups of cells in the dorsal ciliary band, the preoral transverse and adoral ciliary bands in larvae up to the early brachiolarian stage (five weeks). The pattern of serotonin immunoreactivity, although appearing earlier in the apical nerve plexus, is very similar to that of the peptide, with paired groups of immuno- reactivity apparent in the dorsal ciliary band. This evidence, together with other recent studies, indicates that this neuropeptide is present in both the larval and adult nervous system, despite the complete reformation of the system at metamorphosis. The close localization of SI with serotonin may also suggest a possible function for the peptide in larval and adult nervous systems.

Histochemical methods for cholinesterase activities were applied to embryos and early larvae of the marine mussel Mytilus galloprovincklis Lamarck (Mollusca: Bivalvia: Mytilidae) and demonstrated that the cerebral ganglia, which are generally accepted as the first differentiating ganglia, appear after two bilaterally symmetrical nerve rudiments have developed in a posterior position prior to the trochophore stage. They are intimately associated with non-nervous superficial cells in two structures which have features of sensory organs.

The myotomes in yolk-sac larvae of the Atlantic herring (Clupea harengus: Teleostei) contain a single layer of small-diameter superficial muscle fibres surrounding an inner mass of around 280 larger-diameter muscle fibres. The fraction of muscle fibre volume occupied by mitochondria is dependent on temperature, and in larvae reared at 8°C was 41% for the superficial fibres, and 25% for the inner muscle fibres. The inner muscle fibres of larvae share some myofibrillar proteins with adult white muscle, but contain unique isoforms of myosin heavy chains, troponin T, troponin I and myosin light chain 2. A monoclonal antibody has been produced which is specific to myosin light chain 3 (MLC3). Immunocytochemical studies have shown that the expression of MLC3 is switched off in the superficial muscle fibres at the start of metamorphosis when larvae reach 28–30 mm total length (TL). Metamorphosis to the juvenile stage is complete in fish 35–40 mm TL and is also associated with the development of gill filaments and the production of presumptive slow muscle fibres which form externally to the larval superficial muscle fibres in the region of the lateral line nerve.

Acetabularia (Dasycladaceae: Chlorophyta) is a giant unicellular marine alga possessing a single nucleus but several millions of chloroplasts and mitochondria. It presents a polar growth and a peculiar morphological differentiation, comprising the development of a branched rhizoid at its basal end, where the nucleus is located, and the formation of several seriated whorls and then a reproductive cap at the apex of the stalk. Acetabularia is particularly useful in many fields of cellular and molecular biology. Recent work and current ideas on its developmental biology are summarized and discussed.

The winter of 1989/1990 was a year of marked warm water inflow along the Iberian, Spanish and French continental slopes and three anticyclonic eddies developed in the southern Bay of Biscay. Winter temperatures along the northern Spanish slope were examined in the belief that warm water inflow is related to the production of anticyclonic eddies in the southern Bay of Biscay. The annual cycle of temperature (at ~200 m depth) is most unusual in that the warmest temperatures occur in January, the coldest in the summer. Year-to-year variations are evident with the suggestion of a periodicity, though variable, of about five years.

In April 1992, an opportunity presented itself for a late winter eddy survey in the south-eastern corner of the Bay of Biscay from RRS ‘Charles Darwin’. Two Argos buoys were deployed in what was thought to be, or would develop into, an anticyclonic eddy, and one of the buoys was caught in the eddy. This buoy was drogued at a depth of 320 m in a relatively well-mixed part of the water column thought to contain the eddy core. This buoy made ~60 clockwise orbits in the eddy and remained within 15 km of the eddy centre over the 200-d observation period. The normalized relative central vorticity of the eddy had a minimum value of -0·6 and the eddy rotation period experienced by the buoy ranged from 2·5 to 6·5 d. The decay scale for the eddy was estimated at 250 ±100 d. The mean variance of the east-west velocity component was significantly larger than the north-south value, and the buoy's orbit was significantly elliptical towards the end of the period of the observations.

Between 8 May and 3 June 1987 horizontal distribution of Owenia fusiformis larvae (Annelida: Polychaeta) was studied in the eastern part of the Bay of Seine on two spatial scales to determine the role of larval dispersal by hydrodynamic factors on the population dynamics of a benthopelagic species. Larval dispersal occurred in two main directions, north-west and north-east, according to the residual tidal circulation. There was a substantial transport of larvae to a distance of 30–40 NM (48–65 km) from their emission point, resulting in a sizeable loss of larvae to the adult population. However, their densities were low in comparison with those observed in the eastern part of the bay, near the adult population. Larval densities remained highest near the adult population, principally under the influence of tidal processes. In contrast, there was a significant wind-induced larval movement at a time scale of a few days. The action of wind at a time scale of one month, the duration of larval life, appeared to be insignificant for dispersal in 1987 because of the frequent changes in wind direction. Climatological data collected between 1951 and 1980 showed that the wind effect observed in 1987 is probably typical of most years. The horizontal transport of Owenia fusiformis larvae, combined with the ontogenic vertical migration observed previously, causes a retention of these larvae in the eastern part of the Bay of Seine; this favours recruitment and may be one of the factors explaining the temporal stability of the adult population.

Tolerance and behaviour to hypoxia and anoxia by the annelid Loimia medusa (Savigny) (Polychaeta: Terebellidae), a common species in estuarine habitats where summer hypoxic events often occur, were examined in the laboratory. The worm can tolerate anoxia or severe hypoxia (7% air saturation at 26°C) for 3 to 5 d. Under low dissolved oxygen (<14% air saturation) feeding stops, although tube irrigation continues and periodic protrusions from the tube are common. Most worms come out to the sediment surface, but the number of worms dead on the surface is higher in anoxia than in hypoxia. The prevalence of L. medusa in deep estuarine channels may be partially explained by its tolerance to prolonged periods of hypoxia (14 d at 14% air saturation). Our data, however, suggest that subtle changes in oxygen concentrations may be important in the control of populations of L. medusa in habitats affected by low oxygen disturbances.

Members of the Haptophyta from British waters have been listed in a number of check-lists between 1953 and 1976 (Parke, 1953; Parke & Dixon, 1964, 1968, 1976), but there has been no attempt to draw the records together on a world-wide basis. However, a recent review of the classification system of the coccolithophorids included a check-list of all species thought to be extant from marine, coastal and freshwater habitats (Jordan & Kleijne, 1994). At the same time, two ambitious projects, the Encyclopaedia of Algal Genera (ed. B.C. Parker, in preparation) and the preparation of a CD-ROM retrieval system for information on algal and protist groups by the Expert-Centre for Taxonomic Identification (ETI), have required further collation of the available records (see Note 1), and, as a result, we have now extended the scheme of Jordan & Kleijne (1994) to include a global list of all extant haptophytes.

The global distribution of the 12 described, deep-living megacalanid species is presented in a report on collections made in the Southern Ocean during the United States Antarctic Research Program. Included are four species and one subspecies described in 1967 from samples obtained early in the program. In the material lent to the author by the Smithsonian Oceanographic Sorting Center, only six of the described species were found. Bathycalanus bradyi, common in those samples and elsewhere, is made a synonym of B. richardi. The predominant forms are, in order, B. richardi, Megacalanus princeps, and B. princeps, with Bradycalanus sarsi, B. typicus and B. gigas also present. Knowledge of their distribution and ecology is discussed.

To date, the oedicerotid amphipod Monoculodes gibbosus Chevreux, 1888 is known in British seas from only two individuals collected from Loch Fyne and lodged in the Robertson Collection at Millport (Moore, 1984). Recent intensive research on other species in this family in the Clyde Sea area by one of us (D.J.B.) has resulted in the sporadic capture of further individuals of M. gibbosus (128 individuals in total) from Inchmarnock Water, southern Loch Fyne. This material allows us to expand our knowledge of the species' morphology, live colour, population structure, fecundity, egg size, breeding season, diet and behaviour. Notes on these topics are presented below.

The use of stolons in competitive interactions between several species of bryozoans growing in Townsville Harbour, North Queensland is described. Stolonal growth resulted in overgrowth reversals and redirected growth in interactions between Schizoporella unicornis and Watersipora subtorquata. These results suggest that stolons may play an important role in bryozoan interactions

Two morphotypes of the venerid bivalve Chamelea gallina (L.), viz. C. gallina s.s. and C. striatula, were electrophoretically compared at seven polymorphic enzyme loci. In three populations from the Ría Formosa (southern Portugal), both morphotypes occurred sympatrically. Analyses of genotype frequencies in these mixed populations revealed departures from Hardy-Weinberg expectations at nearly all loci. These deviations were mainly attributable to a Wahlund effect, caused by mixing the two morphotypes. Nei's mean unbiased genetic distance between the two forms was D=1·138, while the mean genetic distances between populations within morphotypes were D=0·083 in C. gallina s.s. and D=0·229 in C. striatula. It is therefore concluded that C. gallina and C. striatula are reproductively isolated (biological) species, the geographical distribution of which is outlined.

The cellular composition of the mantle tissue of Mytilus edulis L. was determined, using quantitative microscopy (stereology) techniques, in three populations of mussels from differing environments, and the data compared. The results indicated that mussels from an estuarine or sheltered coastal environment had a greater proportion of adipogranular tissue than animals from an exposed, open coastal environment. The difference in cellular composition was attributed to differences in nutrient availability in the water column between the various sites. A 15-month transplantation of mussels from an open coast to estuarine conditions resulted in a decrease in the proportion of vesicular connective tissue in the mantle and an increase in gamete production. This suggests that Mytilus edulis can exhibit a high degree of phenotypic plasticity by using not only the more conservative strategy of nutrient storage during periods of high food availability, but also the more opportunistic approach of maximizing gamete production when conditions are favourable.

The development of the female gonad in Loripes lucinalis (Lamarck) from Brest Harbour (Brittany, France) was examined over a one-year period. Throughout the year, several size classes of eggs were observed, and spawning was seen to occur twice. A major spawning occurred in May leaving the gonad completely empty in June. A minor spawning is also thought to have occurred between the November and December sampling periods. These spawnings do not seem to correlate with the classical environmental factors often associated with gametogenesis and spawning, namely temperature and chlorophyll a levels. The energy for gametogenesis seems to be obtained from the transfer of metabolites to the oocytes via specialized follicle cells. These metabolites are believed to be of heterosynthetic origin. An inverse relationship exists between the thickness of the follicle cell epithelium and the occupancy level of the gametes. During periods of gonadal proliferation, these cells represent the nutritive cells of the gonad, but during periods of non-proliferation they make up a somatic tissue used for metabolite storage until conditions are adequate for gonadal development.