The ciliate Cryptocaryon irritans Brown, 1951 is a parasite of tropical marine fishes, being recorded chiefly from coral reef species (Laird, 1956; Burgess, 1978; Colorni, 1985). The disease, cryptocaryosis, accounts for fish mortalities in aquaria (De Graaf, 1973) and mariculture systems (Huff & Burns, 1981; Colorni, 1985; Kaige & Miyazaki, 1985; Rasheed, 1989); however, relatively few studies have been undertaken on the biology of C. irritans, as highlighted by Lorn & Dykova (1992). Sikama (1937) described the major features of the life cycle, infection of the fish epidermis alternating with a free-living phase of reproduction within a protective cyst. Most other investigations of C. irritans have been concerned with morphology (Sikama, 1937, 1938; Brown, 1951, 1963; Nigrelli & Ruggieri, 1966; Cheung et al., 1981; Colorni, 1988) with a recent work on the ultrastructure of the pellicle (Matthews et al., 1993). Little is known regarding the behaviour of free-living stages and the possible influence of environmental factors on transmission. Nigrelli & Ruggieri (1966) noted photopositive responses in theronts. The establishment and maintenance of C. irritans in mullet under controlled conditions (Burgess & Matthews, 1994) provided an opportunity further to investigate light in the survival strategy of this fish pathogen.

The antifouling performance of the dogfish Scyliorhinus canicula (L.) (Elasmobranchii: Squaliformes) eggcase-embryo combination was studied under experimental conditions, in conjunction with an analysis of fouling on wild cases. The cases were shown to develop an external heterogeneous microbial biofilm, and an internal heterogeneous microbial biofilm (when the case opens) composed primarily of cocci and bacilli. Macrofouling was limited on egg-cases (unless kept under high light intensities). Macrofouling ranged from <5% (recently laid cases) to 42% (>300 days exposure). This is a better performance than many commercial antifouling treatments. There was no evidence that the embryo was involved in the antifouling process. A priori, three hypotheses are suggested that might explain the antifouling mechanism of the dogfish eggcase-embryo combination: (1) the yolk/albumin/embryo emit antifouling chemicals; (2) a bacterial culture develops that prevents further fouling; (3) the case with/without an embryo has antifouling properties. The results presented here support the third hypothesis.

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 mysid diets by gut contents analysis have generally revealed a broadly omnivorous feeding habit, but there are also tendencies towards carnivory, herbivory and/or detritivory (e.g. Nath & Pillai, 1973; Siegfried & Kopache, 1980; Mauchline, 1980; Zagursky & Feller, 1985; Wooldridge & Bailey, 1982; Webb & Wooldridge, 1989). Examination of feeding structures is also necessary to support inferences about feeding ecology (e.g. Webb & Wooldridge, 1989). However, there have been few studies relating to the functional morphology of mysid foreguts (Gelderd, 1909; Haffer, 1965; Nath & Pillai, 1973; Mauchline, 1980; Friesen et al., 1986; Webb & Wooldridge, 1989; Storch, 1989). With the exception of the latter two studies, qualitative descriptions and characterization of the different internal foregut structures have been primarily based on light microscopy. These studies may misinterpret the internal arrangement, topography, and three-dimensional orientation of the internal armature of the foregut, mainly due to problems with depth of field (Grice & Lawson, 1971). Oshel & Steele (1988), from SEM observations, briefly described some foregut features of Gnathophausia ingens. In a comparative study, Storch (1989), using the techniques of transmission and scanning electron microscopy, described in detail the different food chambers and channels, cuticular ridges, and ultrastructure of the epithelial and cuticular linings of the mysid foregut. Webb & Wooldridge (1989) noted the strong relationship between mouthparts, foregut morphology, and the feeding habits of two co-occurring mysids.

Snapper Pagrus auratus (Bloch & Schneider) (Pisces: Sparidae) larvae are visual feeders which initiate exogenous feeding four days after hatching. Visual acuity of cultured snapper larvae was determined morphologically from cone spacing within the retina, and improved from 2°10’ minimum separable angle (MSA) in a 4-d-old larva (3·2 mm SL) to 52’ in a fish 22 d old (5·8 mm SL). Visual acuity determined behaviourally using the optokinetic response, was poorer at the time of first feeding than acuity determined morphologically. Behaviourally determined acuity improved with growth from 38° in 4-d-old fish (mean SL 3·1 mm) to 8°8’ at 16 d of age (mean SL 4·9 mm). This was still lower than the theoretical estimate of acuity (55’ at 18 d old, 5·9 mm SL). An estimate of the Matthiessen ratio based upon histological measurements suggests that the larval eye is initially strongly myopic and grows into focus. Development of the lens accommodative system was first apparent in fish at 4 d of age as a pigmented outgrowth of the ventral iris. A retractor lentis muscle was present in 7-d-old larvae (3·5 mm SL) and suspensory ligaments were present in 10-d-old fish (3·6 mm SL). As a consequence, larval snapper were initially incapable of accommodative lens movements to correct for a refractive error. The maximum internal jaw dimensions, an estimate of maximum ingestible prey size, ranged from 152 μn at first feeding to 373 μm in a 22 d old larva. Reactive distance to prey based on MSA determined from the optokinetic response and maximum prey width, were small in first-feeding fish (0·2 mm for prey width of 150 μm), but increased linearly with both body size and prey width. Minimum separable angles of first-feeding snapper deter-mined optokinetically, were larger (lower acuity) than the visual angles determined from feeding events of first-feeding fish larvae reported elsewhere. This may reflect the fact that optokinetic experiments involve a single sensory modality and chemical sense and developing lateral line may contribute to visually oriented feeding.

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.

The incidental capture of sharks in the bottom-set gill-net fishery off the south coast of Ireland was quantified by placing observers on commercial gill-netters for the duration of a fishing trip. Forty fishing trips were sampled resulting in 1,167 km and 19,760 km h of observed fishing effort. Sixty individual sharks of seven species were reported entangled in the fishing gear. Tope, porbeagle and six-gilled sharks were the most frequently caught species, with black-mouthed dogfish, blue shark, basking shark and starry smooth hound also recorded. Total fishing effort along the south coast was calculated and total capture extrapolated from observed catch rates. An estimated 6,000 sharks were caught in this fishery during the study period.

A first quantitative description of the suprabenthic fauna in a coarse sand community from the western English Channel is provided. One hundred and twenty species of Crustacea were collected in 22 suprabenthic sledge hauls collected throughout the year (1988–1989). Mysids and Amphipods dominated the fauna, among them Anchialina agilis (Sars), Gastrosaccus spp., Apherusa spp., Eusirus longipes Boeck, and Stenothoe marina (Bate) were the dominant species. Although most dominant species showed a vertically decreasing gradient of density from the lower net to the upper level of the sledge, the most abundant species, Apherusa spp., showed similar density at all four levels. The mean density at the four levels of the sledge did not differ significantly with the distance above the sediment. Species performed nocturnal vertical migrations: the densities of mysids were higher during the day than at night; conversely, the densities of amphipods and decapods were higher at night than during the day. The density and species richness showed high seasonal variation, from low values at the end of autumn and winter to high values in summer and the beginning of autumn. The results are compared with the available data on suprabenthic communities from the North Atlantic; this highlights (1) the lack of concentration of suprabenthic fauna towards the sediment on coarse sand, and (2) the highest abundance of the suprabenthic fauna from muddy substrata.

Since the introduction of the Manila clam Ruditapes philippinarum (Mollusca: Bivalvia) to aquaculture clam beds, this species has spread to several sites. As a result, an extensive fishery has developed around this species. Its reproductive cycle and that of a native clam species, Ruditapes decussatus (Mollusca: Bivalvia) from two Brittany sites are examined here and the seasonal variations in the condition index, the scale of maturation stages, the histology and the oocyte size-frequencies of both species are compared. The differences observed between the species and between sites were attributed to environmental conditions. Ruditapes philippinarum showed a more extended breeding period and a greater number of spawning events than R. decussatus. In the Morbihan Gulf, the reproductive activity of R. philippinarum appeared particularly great in terms of number of spawning events, and speed of maturation. For both species, synchronism was more apparent during the first maturation, while spawning, and particularly partial spawning, tended to decrease the level of synchronization.

The recruitment and succession of fouling organisms was examined on four substrata (concrete, plywood, fibreglass and aluminium) in Quibray Bay of Botany Bay in New South Wales, Australia. Eighteen 10×10 cm panels of each substratum were submersed in each of four seasons: January (summer), March (autumn), May (winter) and October (spring) 1992. Six of each substratum were retrieved after 1 month, 2 months and 4–5 months. Thus in this study, as a methodological improvement over many other studies of succession, samples were taken independently with regard to time.

Seasonal recruitment was important in determining the pattern of succession and the composition of the assemblage. Sydney Rock oysters, Saccostrea commercialis (Iredale & Roughley), recruited in large numbers on panels submersed in January and, by their rapid growth, dominated the available space after 4–5 months. The greatest recruitment of the barnacle Hexaminius sp. and the greatest percentage cover of algae (six species) occurred on panels submersed from October to March. While panels submersed in January for a period of 4–5 months resulted in a single outcome, an oyster-dominated assemblage, panels submersed in October for the same period of time resulted in a set of alternative outcomes depending on the relative abundance of barnacles and algae.

The in situ growth rates of marine planktonic ciliates from Plymouth Sound were determined after fractionating the natural community into several size categories to remove predators of different sizes. Total community in situ growth rates varied from 0·01 to 0·57 d−1 according to fractionation treatment, with the four most abundant taxa, comprising three species of Strombidium, and Mesodinium rubrum, achieving maximum in situ growth rates of between 0·41 and 0·68 d−1. These values are approximately half the maximum theoretical rates calculated indirectly using an equation which relates ciliate growth to cell size and temperature. Given the conservative nature of in situ growth rate measurements, the growth rates reported here appear appropriate for a natural ciliate community growing within a nutritionally favourable environment.

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.

The summer vertical distribution of appendicularian species was analysed at 22 stations in the central Cantabrian Sea by means of vertical tows covering the surface, thermocline and deep layers. According to their preference for shallower waters, the appendicularian species could be arranged on the series Oikopleura longicauda (Vogt), Oikopleura fusiformis (Fol), Fritillaria pellucida (Quoy & Gaimard) and Oikopleura rufescens (Fol), with Oikopleura dioica (Miiller) in an uncertain position, probably closer to the end of this series. Principal components and correlation analyses suggest that a temperature gradient causes this pattern, which agrees with previous findings made at very different temporal and spatial scales. By means of particle-size spectra, it is shown that those oikopleurids that prefer cold, deep waters, O. fusiformis and O. rufescens, co-vary with a coefficient of particle-size quality. The lower the temperature, the lower the proportion of small, ingestible particles to large inlet-filter-clogging particles. This is proposed as an important reason for the presence of inlet filters in oikopleurids.

Two erect species of bryozoans, Alloeflustra tenuis (Kluge) and Nematoflustra flagellata (Waters), occur abundantly in similar localities at Signy Island, Antarctica. Both species are unilaminar and are colonized by a range of epibiotic taxa, principally other cheilostome bryozoans. A detailed study was undertaken of the bryozoan epibiota of these two species, collected by SCUBA over the depth range 36 to 40 m. The degree of colonization varied with host size and differed between the front and rear surfaces of each host species, and between host species. The species composition of the epibiota was also different between species and between surfaces within species. These variations are possibly related to differences between the host species in the abundance, structure and function of avicularia (putative protective structures). Specimens from deeper water (150 m) showed significantly reduced colonization by epibiota, but the same overall patterns of colonization between the two species and surfaces were still observed.

During a study based on catches taken in the northern North Sea by selected Scottish fishing boats during 1985–1992, large numbers of the normally rare short-fin squid, Todaropsis eblanae (Cephalopoda: Ommastrephidae), were recorded in 1987 and 1990. Our findings, supported by data obtained from plankton/young fish surveys in 1988 and 1989, suggest that in northern waters Todaropsis eblanae generally mates and spawns during late summer and early autumn (June-November). Successful hatching events appear to occur during October-March, producing juvenile (stage I) squid in the early part of the year (January-June). Estimations of maximum male reproductive output and female fecundity were up to 130 spermatophores and ~28,000 eggs per individual, respectively.

The gross morphology, histology, ultrastructure and periodicity of gonad development of the bathyal aspidochirote holothurian Bathyplotes natans is described and compared with the ‘tubule recruitment model’ proposed for aspidochirote holothurians. As B. natans grows, additional gonad tubules develop at the anterior end of the gonad basis. Oocyte development in these tubules is non-seasonal and the population of oocytes consists of both pre-vitellogenic and vitellogenic oocytes as well as some large oocytes undergoing phagocytic breakdown. Vitellogenesis is similar to that described previously for holothurians, although the follicular inner epithelium cells surrounding the developing oocytes are different from those previously reported. In males the unique acrosomal complex consists of three depressions with the acrosome lying in the central depression. The tubule recruitment model of Smiley does not apply to B. natans. We do not feel this model has widespread applicability in the Aspidochirotida or the Holothurioidea in general.

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 species composition, abundance and spatial distribution of macroplanktonic cnidarians in the eastern part of the Weddell Gyre are described from a series of nekton samples collected over three depth ranges between 0 and 2000 m. On average, cnidarians contributed 52·6% to the biovolume of these samples, although the range was high (5·0–93·1%). In total 23 species of siphonophores and 20 species of medusae were identified; a number that is very high in comparison with previous studies. There was a high diversity at bathypelagic depths, with 38 species being collected below 1000 m. The most abundant siphonophores were Dimophyes arctica (up to 45 nectophores per 104 m3) and Heteropyramis crystallina (up to 22 nectophores per 104 m3). The most abundant medusa was Pantachogon haeckeli (up to 30 specimens per 104 m3). Medusae were most abundant at mesopelagic depths, reaching 46 specimens per 104 m3 in the 500–1000 m depth range. Smaller calycophoran siphonophores were concentrated in the top 500 m of the water column, with total numbers averaging 107 per 104 m3. The number of larger calycophorans in-creased with depth, being most abundant in the 1000–2000 m depth range. Although many species had a widespread geographical distribution within the sampling area, the hydrographical conditions appeared to be affecting the distribution of some.

This field study examined competition for space among encrusting bryozoans on artificial panel substrata used to simulate the habitat found on the undersides of boulders. In all 1761 interactions were analysed, involving 16 species of cheilostomes (genera Callopora, Celleporella, Cribrilina, Electra, Escharella, Escharoides, Haplopoma, Membraniporella, Microporella, Phaeostachys, Schizomavella, Schizoporella and Umbonula) and two ctenostome genera (Alcyonidium and Flustrellidra). Neither absolutely transitive nor intransitive arrangements of competitive outcome occurred among the species. Instead, the high incidence of ‘ties’ and reversals of outcome produced a network-like arrangement. In terms of outcome alone Escharoides coccinea (Abildgaard), Membraniporella nitida (Johnston) and Schizoporella unicornis (Johnston in Wood) were apparently ‘overgrowth dominants’, Alcyonidium spp. and Cribrilina cryptooecium Norman were ‘intermediate dominants’ and Callopora lineata (L.), Callopora craticula (Alder), Celleporella hyalina (L.) and Electra pilosa (L.) were ‘inferior competitors’ for space. The effects of four variables on the outcome of specific competitive encounters were assessed in detail and included (i) the identity of the colony encountered, (ii) the angle of contact between the competing colonies, (iii) the location (two sites, on both the east and west coasts of Scotland) and (iv) the year (1983, 1984). Models incorporating these variables were developed, using the Generalized Linear Interactive Modelling System (GLIM), to examine their influence on the outcome of bryozoan encounters. All of these factors contributed to explaining the considerable variability in the outcome of competitive interactions. The species were not, however, affected equally by all the variables, although encounter angle and year were significant for dominants and encounter angle, site and year all were significant for intermediate species.