The stenophagous ascoglossan (=sacoglossan) opisthobranch Elysia viridis has long been a model organism for the study of endosymbiosis or kleptoplasty as well as one of the few herbivores to consume the introduced green macroalga Codium fragile on European shores. Larval and post-larval dynamics of the ascoglossan were investigated. Planktotrophic larvae of E. viridis grew at 5–10 μm d−1 (shell length) at 15°C on a unicellular algal diet (the cryptophyte Rhodomonas baltica); larvae became competent one month post-hatching. Effective feeding and chloroplast acquisition typically started within 2–3 d of metamorphosis. Slugs grew about 8 mm in the first month of post-larval life. During this period, juveniles held in the light did not grow faster or survive better than conspecifics held in the dark; thus, functional kleptoplasty did not occur during first three weeks of benthic life. While larval growth rates and the nature of metamorphic cues are consistent with those of many other opisthobranch species with planktotrophic larvae, measures of post-larval growth—particularly as it pertains to kleptoplasty—is a new contribution to opisthobranch biology.

The ascidian Corella inflata (Chordata, Ascidiacea) is common in many areas of Puget Sound, Washington, USA. However, it occurs only in habitats where it is protected from direct sunlight. Previous experiments with artificial lights showed that UV irradiation kills all life stages of this animal. The effects of natural sunlight exposure (measuring survival of adults, juveniles, larvae, and embryos) were compared. We partitioned the light spectrum to separate the effects of UVB, UVA, and visible light (PAR). Natural sunlight severely damaged C. inflata. Adults and juveniles died after 2-5 d. Exposed embryos failed to develop normally and larvae did not settle. As expected, UVB had significant effects, but pronounced effects were also seen when the animals were exposed to longer wavelengths alone (UVA and PAR). Thus, the distribution of C. inflata may be determined largely by exposure to light. Understanding the basic ecology of this species requires consideration of its vulnerability to sunlight damage and the effects of UVB, UVA, and PAR.

The dominant lipids of seven species of abyssal holothurians (Oneirophanta mutabilis, Pseudostichopus villosus, Psychropotes longicauda, Deima validium, Parariza prouhoi, Amperima rosea and Molpadia blakei) have been examined in detail. Fatty acid compositions are qualitatively similar to those of shallow-water holothurians, but relatively higher amounts of unsaturated compounds in the deep sea animals are ascribed to an adaptation of the latter to maintain membrane fluidity at high pressure and low temperature. The sterol distributions of abyssal holothurians are complex, with mixtures of C26–C30 sterols being present in all of the animals. These are most likely to be dietary in origin; the holothurians substitute Δ5 with Δ7 unsaturation, via Δ5,7 or Δ0 intermediates. 14α-methylcholest-9(11)-enol, which is a common product of de novo biosynthesis in shallow-water holothurians is absent in all of the deep-water species. Furthermore, cholest-7-enol, the dominant product of de novo biosynthesis in shallow water animals, is a relatively minor component in all of the species, except A. rosea. This holothurian is also the only one that appears to assimilate 4α-methylsterols directly and contains high amounts of steryl sulphates. There are significant interspecies differences in the free sterol distributions which may reflect their different feeding strategies or niches.

A study was carried out on the morphology (size and shape) of the saccular otolith (sagitta) by means of image analysis on three species of the genus Merluccius (M. gayi, M. hubbsi and M. merluccius). By digitization of the sagittae, morphometry and outline (Fourier harmonic) as form descriptor measurements were obtained, that were subsequently analysed by means of multivariant methods, allowing the intraspecific variability to be quantified. The differences in the intraspecific sagittal otolith variability confirmed spatial differences of predicted groups. The results were associated with environmental and population aspects. The use of combined morphometric measurements for the whole otolith and its corresponding sulcus acusticus were very appropriate for determining the origin of the analysed otoliths. Using both principal components analysis and discriminant analyses, a clear geographical differentiation was obtained for Merluccius gayi (from Chile and Peru) and M. merluccius (from the Atlantic and Mediterranean). In both species, the discriminant analysis predicted that all the sagittae could be correctly assigned within each of the groups studied. However, it was a little less effective at differentiating between the two groups of M. hubbsi (from the San Matias Gulf on the Patagonian Shelf and Argentinian–Uruguayan Common Fishing Zone). As a result, the morphometric analysis of the sagittae otoliths acted as a clear diagnostic tool to differentiate individuals from different geographical distribution areas.

Sponge communities were sampled at 3 m depth intervals at six sites experiencing different flow regimes at Lough Hyne, Ireland. Sponges were identified and classified within the following morphological groups: encrusting, massive, globular, pedunculate, tubular, flabellate, arborescent, repent and papillate morphological types on both vertical (≈90°) and inclined (≈45°) surfaces.

Differences in the proportional abundance of the sponge body forms and density (sponge m−2) were observed between sites and depths. The density of sponges increased with depth at sites of slight to moderate current flow, but not at the site where current flow was turbulent. Morphological diversity of sponge communities decreased with increasing current flow due to the removal of delicate forms such as pedunculate and arborescent shaped sponges. Massive and encrusting morphologies dominated at the high-energy sites (fast and turbulent flow regimes) due to a high basal area to volume ratio, which prevents removal from cliff surfaces. However, pedunculate, papillate and arborescent types dominated at the low current sites as these shapes may help to prevent the settlement of sediment on sponge surfaces. Bray–Curtis Similarity analysis and Correspondence Analysis were used to distinguish between five different morphological communities.

The observation in natural conditions of headless chaetognaths with healed scars and ripe gonads led us to reproduce this condition experimentally. Histological sections were made on specimens of Sagitta and Spadella at different times after beheading. The muscles contract and the gut closes the wound, so that by the end of the first two hours, the body wall and gut ‘basement membranes’ are in continuity, so restoring the integrity of the body. After two hours, the muscular layer of the body wall is reshaped and closes up the wound; the gut seals off, and a ‘clot’ is evident in the wound area. The benthic Spadella cephaloptera survives some 30 d or more after decapitation. Specimens carrying ripe ova were able to lay them, to mature and fill their seminal vesicles once or twice and to mate with normal mature specimens. Headless chaetognaths must take up nutrients through the integument. It appears that chaetognaths cannot really regenerate head or tail tip.

This note examines the way the pharyngeal feeding filter is constructed within the salp endostyle. Three salp species (Pegea confoederata, Thalia democratica and Salpa fusiformis) have been examined: results from each are essentially similar. The endostyle is a deep ventral groove in the pharynx, divided by a line of long basal cilia. These are flanked by gland cells which secrete the ‘mucus” which forms one of the sets of filaments of the filter. Beside the openings of this basal row of gland cells (marked by bumps of curious ‘mucus’ rodlets), there is a fence of two adjacent rows of cilia. The first of these two rows, (nearest the basal mid-line), whose tips lie next to the rodlet bumps, are regularly spaced 1.0 μm apart along the endostyle, whilst the cilia of the second row are at around half this spacing. Passing upwards in the endostylar groove, this first ciliary fence is followed by a ciliated zone, and then a second row of glandular cells is linked to a second ciliary fence with a single row of cilia only.

Filaments derived from the first set of gland cells pass obliquely over the ciliated zone, and continue over the second ciliary fence. The cilia of the second fence are often surrounded by very striking borders or curtains of rodlets which appear to dissolve, run down the cilia and pass off the tips as filaments, when they are joined by the first set of filaments to form a net with an elongate rhomboidal mesh. As this passes upwards, the mesh changes to become more or less square by the time it comes to overlie a striking asymmetrical band of cilia arranged in columns, when it is now composed of two sets of filaments running vertically and horizontally, spaced some 1.3 μm apart.

Various aspects of the formation of this filter net are considered.

Age and growth of the snipefish was studied based on samples collected in the Portuguese continental waters between 1996 and 1998. Analysis was conducted for two species, Macrorhamphosus scolopax and M. gracilis and for both species combined. Total length ranged from 5.5 to 18.2 cm for M. scolopax and from 5.4 to 17.3 cm for M. gracilis. Length–weight relationships were described for M. scolopax (a=0.00401; b=3.127), M. gracilis (a=0.00459; b=3.006) and both combined (a=0.00240; b=3.282). Age estimation, based on otolith observations, resulted in six and five years maximum age attributed to M. scolopax and M. gracilis, respectively. Back-calculation analysis based on a polynomial relation of the otolith radius on total length provided significantly smaller lengths-at-age compared with observed lengths. The von Bertalanffy growth curves fitted to observed lengths-at-age provided parameters of L∞=15.7 cm, K=0.654, t0=−1.066 for M. scolopax; L∞=14.2 cm, K=0.694, t0=−0.954 for M. gracilis and L∞=15.8 cm, K=0.470, t0=−1.408 for both species combined.

Giemsa-stained blood smears were examined from 70 deep demersal fish of 27 species in 20 genera, trawled from depths of 747–4143 m in the region of the Porcupine Seabight, north-east Atlantic. Infections were found in four species of teleosts in three families: 1/3 Alepocephalus rostratus and 1/3 Narcetes stomias (Alepocephalidae); 2/3 Antimora rostrata (Moridae); and 1/1 Cataetyx laticeps (Bythitidae). Blood films from C. laticeps and Antimora rostrata were well preserved but those from the other two species were less satisfactory. The blood parasites included two types of haemogregarines, Haemohormidium-like and viral erythrocytic necrosis (VEN)-like infections. Haemogregarina (sensu lato) johnstoni sp. nov. was described from C. laticeps captured at 1541 m. This haemogregarine was unusual in apparently having dimorphic gamonts, some with prominent caps. A second, but monomorphic, haemogregarine found in Alepocephalus rostratus captured from 985 m, was named as Desseria sp. since only extracellular stages were observed. Haemohormidium-like organisms were found in Antimora rostrata taken from 2441 m, and were similar to those described previously from this deep-sea fish. A VEN-like infection from one N. stomias captured from 2567 m was reported. No marked effects on host cells were evident in any of these blood infections.

The concentration of phytoplankton chlorophyll-a (chl-a) and primary production within the euphotic zone (at depths corresponding to 100, 30, 10 and 2% light) were measured in the oceanic region of the Oyashio Water, the north-western Pacific, in spring of 1993, 1994 and 1995. The chl-a concentrations ranged from 0.15 to 6.98 mg m−3 and the range of chl-a standing stock integrated from the surface to the 2% light depth was between 4 and 43 mg m−2. The daily primary production integrated from the surface to the 2 and 0.2% light depths was estimated to be between 94 and 1695 mg C m−2 d−1 and between 114 and 2046 mg C m−2 d−1, respectively. Phytoplankton bloom was noticed when the depths of the euphotic zone and the upper mixed layer were similar. The maximum chl-a concentration and daily primary production in the upper 0.2% light depth were comparable to those reported previously in the spring bloom in the coastal, offshore and oceanic regions of the Oyashio Water, and in the summer bloom of the Western Subarctic Gyre in the North Pacific. The magnitude of daily primary production in the phytoplankton bloom in the western subarctic North Pacific (the Oyashio Water and the Western Subarctic Gyre) was comparable with those in the eastern subarctic North Pacific and the subarctic North Atlantic. The magnitude of chl-a in the phytoplankton bloom in the western subarctic North Pacific was higher than those in the other subarctic regions. Varied contribution of large diatoms to the phytoplankton biomass, caused by different iron and silicate conditions was hypothesized to be a leading factor for variation in magnitude of the phytoplankton biomass.

Development of the olfactory system in anemonefish embryos of the species Amphiprion melanopus was examined from day six post-fertilization, until hatching (day nine). An olfactory placode with receptor cells lining the epithelium and nerve axons from the placode into the olfactory bulb, was observed on newly hatched embryos. In addition, two different secondary bilateral receptor systems were found. These findings may firstly support the anemonefish host imprinting hypothesis, and secondly indicate that the ontogenetic timing of this imprinting mechanism occurs towards the end of the embryonic development.

Numerous studies of their population genetics have reported incipient reproductive isolation among sympatric populations of the common intertidal beadlet anemone Actinia equina. This has lead to certain morphs being raised to specific status. A study of the nematocysts of the green sea anemone Actinia prasina and three genetically isolated morphs of A. equina was undertaken to establish that mean nematocyst length could act as diagnostic phenotypic characters within a morphologically variable group. The results support genetic and ecological evidence for the specific status of the three red/brown coloured morphs of A. equina. The data are discussed with respect to the ecology of Actinia and concepts of species, but more work is required before the specific status of A. prasina can be confirmed.

The spawning of Paracentrotus lividus has been determined on the basis of the annual gonad index cycle at three sites in the Algiers area presenting low, intermediate and strong hydrodynamism. Three biotopes (Posidonia oceanica beds, rocky substrate with photophilous algae and overgrazed rocky substrate) and two depths (1–3 m and 6–10 m) were considered at these sites, the sex-ratio was always strongly in favour of females (2:1 to 3:1). In all sites but one, there were marked differences in the gonad index and the spawning period between sites; the gonad index reached its maximum value at the site with the weakest hydrodynamism, and the minimum value at the site with the strongest hydrodynamism. Spawning took place in April–May and August–September at the site with the weakest hydrodynamism, in April–June and October–December at the site with intermediate hydrodynamism and only in winter at the site with maximum hydrodynamism. The coexistence, on regional scale, of these reproductive cycles might enable Paracentrotus lividus to compensate the mortality during planktonic larval phase by the fact that spawning of this sea urchin occurred in all seasons.

Nitzschia alba (Bacillariophyceae), a colourless (apochlorotic) pennate diatom, was found on the surface of seaweeds collected from the Clyde Sea area between August and December, 1994. This is the first record of N. alba in UK waters. Nitzschia was found to replicate much more rapidly than heterotrophic protists of similar size. At 20°C, cells divided in just 6.9 h and even at 5°C the generation time was only 38.2 h. The ecological importance of these diatoms has been overlooked by microbial ecologists despite the high productivity of coastal ecosystems and recent work that has shown that Nitzschia can utilize seaweed phycocolloids and invade damaged seaweed tissue.

The pit organs (free neuromasts) of sharks are part of the lateral line sensory system, but there is still confusion about their exact morphology and function(s). This is partly because of reported physiological differences between the pit organs and the lateral line canal neuromasts, and partly because the morphology of pit organs has not been adequately documented. To compare their morphology, the pit organs and canal neuromasts of the gummy shark Mustelus antarcticus (Chondrichthyes: Triakidae) were examined using transmission and scanning electron microscopy. Both pit organs and canal neuromasts had hair cells with the `staircase' arrangement of sensory hairs (stereovilli) characteristic of vertebrate mechanoreceptors. Stereovilli bundles of different sizes were distributed haphazardly throughout the pit organs and canal neuromasts. The density of hair cells was similar in the pit organs and canal neuromasts, but differences in the overall size and/or shape of the sensory epithelia might account for some of the reported differences in mechanosensitivity.

The velocity of sound through spermaceti oil from the melon of two Kogia sima specimens, stranded in Florida in 1995, was determined across a range of temperatures between 7 and 38°C and at pressures between 0 and 90 atm. Sound velocity values ranged between 1395-1669 m s−1, increasing linearly with increasing pressure but decreasing non-linearly with increasing temperature. Polynomials were generated to describe sound velocity as a function of temperature and pressure for the core and peripheral lipids of the melon. The results suggest that, at normal body temperature, sound travelling from the back to the front of the melon would have a tendency to focus during dives to any depth, largely due to heat exchange across the periphery of the melon. Effects of changes in ambient temperature and pressure are described and discussed in relation to anatomy.

Multivariate analysis of qualitative and quantitative data from algal communities, collected at three coastal areas of the Aegean Sea in the upper infralittoral zone, has been carried out using the PRIMER software. The aim was to detect groups of species reflecting differences in environmental conditions. A multidimensional scaling of the results demonstrated the presence of three different groups of Cystoseira species, corresponding to different hydrodynamic conditions.

The sea urchin Psammechinus miliaris was sampled at monthly intervals from two replicate sites at contrasting locations (littoral and subtidal habitats) on the west coast of Scotland. Samples were collected from November 1995 to October 1997. A study of gonad development showed a clearly defined annual cycle of gametogenesis with a single spawning period. Gonad indices (GIs) varied between locations, between sites at the same location and between study years. Gonad indices were maximal prior to the onset of the spawning period in June and July. Ripe gametes were shed by dissected urchins from June to September in 1996 and June to August in 1997 coinciding with the time of year when the gonad colour was best in terms of what is desired in the market place. Over winter the GIs were very low and gonads became very dark in colour. Higher summer GIs in the urchins from one littoral site suggested that the urchins there had a seasonal influx of a more nutritious or more abundant food resource. Histological determination of the reproductive state showed that for these food-limited populations high GIs do equate with the spawning period. The gametogenic cycle fits the six stage pattern described for other echinoid species. In females oocytes of various developmental stages were present throughout the annual cycle. Recruitment to the littoral location was monitored over two seasons by quantifying the number of urchins with a test diameter <5 mm appearing in the population. Recruitment appeared variable between sites and between seasons suggesting that the collection of juveniles resulting from natural settlement may not be a reliable alternative to hatchery produced spat. Although P. miliaris has commercial potential when in cultivation, this study provided no evidence of an opportunity for a commercial fishery.

The sea anemone Anemonia viridis is one of the most common species of the North Aegean Sea. The variety in colour morphs exhibited by this species, causes problems to taxonomy and ecology, and suggests that A. viridis should be subdivided into two distinct species according to the colour of the individuals. The approach used in this study was based on the biometrical cnidae characteristics of the two colour morphs (rustica and smaragdina), as it is known that cnidae biometry has been used as a taxonomic tool for the phylum Cnidaria. More than 20,000 nematocysts were measured to try and find a correlation between these measurements and some body parameters indicative of the maturity grade of the individuals, as potential taxonomic characteristics. Stable cnidae characteristics of the two different colour morphs were compared. However, they differed only in the biometry of the tentacles' a-basitrichs. This slight difference does not support the proposal to subdivide Anemonia viridis into two different species.

The effects of polychaete (Lysidice ninetta, L. collaris, Nematonereis unicornis (Annelida: Polychaeta)) and limnoriid isopod (Limnoria tuberculata (Crustacea: Isopoda)) borers in the Mediterranean sea grass Posidonia oceanica (Potamogetonaceae) were assessed in the meadows of Olbia and Genoa (western Mediterranean Sea). Borer invertebrates were mainly found into the old leaf sheaths of the sea grass. At Olbia, a mean density of borers (202.6±34.8 ind m−2) significantly higher than at Genoa (23.2±7.3 ind m−2) was observed. In 3.3% of samples from Olbia, large polychaetes and isopods were also observed boring into living plant tissues. Only fractions from 0.8—3.9% of the sheath production was actually removed by borers at the two studied meadows. The fact that sheath weight loss with time was higher at Genoa than at Olbia regardless of the presence of borers suggests that other factors than the activity of such organisms are important in the sheath decay process.