In this article four species of Desmodoridae, Desmodora alberti sp. nov., Desmodora marci sp. nov., Desmodorella balteata sp. nov. and Desmodorella spineacaudata sp. nov. (Nematoda: Desmodoridae), are described from hydrothermal vents of the Pacific. The genus Desmodora is revised and lists of valid species are provided; four subgenera are reinstated as genera; Xenodesmodora is regarded as genus inquirendum. Definitions of some morphological structures are given.

Tigriopus californicus uses several appendages and processes in the collection and manipulation of food. Their structure and function appear to enable the species to utilize the variety of food materials found in splashpools, including: detritus and organic floes; superficial material on particles; faecal pellets; protists; diatoms; and small crustaceans. From light and scanning electron microscopy and video, the labrum and labium appear to be adapted for biting soft and hard food materials and holding food for trituration by the mandibles. From energy dispersive X-ray spectra, the gnathobase of the mandible is suggested to be sclerotized but not calcified or silicified. It has an array of bilobate and multilobate teeth, clusters of spinous processes, and a heavy, spine-bearing process to move food into the oesophagus. There is also a flange which articulates in a groove in the labrum which appears to provide a guide for the gnathobase as it moves vertically.

Seasonal dynamics of bacterial and heterotrophic nanoflagellate (HNF) species assemblages were analysed in Kaštela Bay (middle Adriatic Sea). Dominant patterns identified were: (1) during summer and autumn bacterial abundance was mainly controlled by HNF grazing (top-down), whereas HNF abundance was controlled by bacterial abundance (bottom-up); (2) during winter and spring the coupling between bacteria and HNF was very weak, and bacterial abundance was mainly controlled by resources supply (bottom-up), whereas HNF abundance was controlled by micro-zooplankton grazing (top-down); (3) throughout the year, both bacterial and HNF species assemblages alternated with two periods of stable abundance, first with high and second with low values; (4) top-down effect was dominant in bacterial switching from stable abundance with high values to stable abundance with low values, whereas bottom-up model dominated in inverse process; and vice versa for HNF.

Consistent with most other closely-related polychaete species which have been analysed cytogenetically to-date, Pomatoceros triqueter and P. lamarckii share an identical chromosome number (2n=24) and have a number of other karyotypic features in common. However, commensurate with their separate species status, their karyotypes differ at least in four chromosome positions as a result of structural chromosomal rearrangements. With a rDNA probe using the FISH technique, we have been able to demonstrate that the nucleolar organizer region (NOR) occurs at the same site on the same pair of chromosomes in the two species, which indicates that an inversion event is unlikely to have been the cause of the species variation in this particular case. Taken together, these karyotypic differences may be indicative of a chromosomal barrier to the formation of fertile offspring; an important feature for maintaining species integrity where the two forms occur sympatrically, such as in parts of south-west England.

The variability in the number of segments in anterior (A) and median (B) regions of adult-size specimens Spiochaetopterus solitarius (Chaetopteridae), was examined in the present study. Variability of region A is considered in relation to the number of specialized setae in A4, which varies from 2 to 4; variability of region B is observed as a decrease in the number of segments during a limited part of the year. A process involving autotomy and regeneration has been advanced to explain the variability in the number of segments in region B. It appears that, once the number of segments in region B reaches a certain level, which is close to 30, the animal divides within region B, and the missing parts of each section are then regenerated. The maximum number of segments in region B may be considered to be species specific and used as a discriminative feature in the genus. It is suggested that regeneration does not reflect asexual multiplication per se, but provides a means to facilitate the supply of energy to region B, which is responsible for bringing the products of the sexual organs to maturity. Consequently, regeneration is considered to complement sexual reproduction, facilitating the availability of energy to region B for reproduction. Implications of this variability have been examined by comparing S. solitarius and S. costarum, two species closely related by their morphology, sympatry and syntopy.

Eight marine oligotrichous ciliates including one new genus, two new combinations, and five new species collected from the Yellow Sea, north-eastern China, are morphologically and biometrically investigated based on observations of living specimens and permanent preparations after protargol impregnation: Strombidium tintinnodes; Novistrombidium testaceum gen. nov., comb. nov. (formerly Strombidium testaceum); Tontonia turbinata sp. nov.; Pelagostrobilidium simile sp. nov.; Rimostrombidium orientale sp. nov.; Strombidinopsis elongata sp. nov.; Strombidinopsis elegans sp. nov., and Strombidinopsis minima comb. nov. (formerly Strobilidium minimum). Four junior synonyms are considered: Strombidium oculatum; S. obliquum; S. hadai and Strombidinopsis cheshiri. A comparison with other known members within Strombidiidae resulted in the establishment of a new genus, Novistrombidium gen. nov. It is similar to Strombidium but characterized by the conspicuously opened girdle kinety with a large gap on its ventral side, through which the ventral kinety extends.

The rDNA repeat-unit of the vent polychaete Alvinella pompejana was investigated using restriction analysis. Mapping revealed evidence of rDNA polymorphism within and between individuals which was due to individual restriction site variation and sequence rearrangements involving spacer regions. The size of the repeat unit was 10.5 kb with virtually no evidence of length variation. Sequence inversions indicated the presence of two spatially-distinct subfamilies of repeats, probably on different chromosome pairs. Animals from contrasting vent habitats with respect to age and chemical emissions (young vs old chimneys and white vs black smokers) from within the 13°N/EPR (East Pacific Rise) vent sector were analysed for evidence of population differentiation. Based on individual restriction site variation, average FST estimates across neighbouring populations were in the region of ~0.05 and differed significantly from zero. This level of genetic differentiation is comparable to values reported previously for allozymes. Spatial and temporal allelic frequency variances estimated from pairwise combinations (i.e. s2S and s2T) strongly suggested that differences in allelic frequency were the result of repeated extinction/recolonization events associated with the vent instability. Estimates of the effective population size derived from standardized temporal allelic frequency variances Fks were very low compared to actual population size indicating great temporal fluctuations in the former. Theoretically, such an effective population size is not sufficient to maintain the observed level of polymorphism within the 13N/EPR vent sector. Results are therefore consistent with a ‘propagule’ colonization-type model in which extinction/recolonization rates are high. In Alvinella, planktonic larval dispersal appears sufficient to overcome any genetic differentiation resulting from drift, but these findings also indicate that propagules may only be capable of dispersing a few tens of kilometres per generation.

The study describes the seasonal density and age structure for splashpool metapopulations of Tigriopus californicus (Copepoda: Harpacticoida). Natural populations were highly variable, ranging from 217 ± 401·7 ind 1−1 in winter (mean ± SE) to 835 ± 1750·6 ind 1−1 in summer, with some populations approaching 20,000 ind 1−1 in all seasons except winter. Male-to-female ratio ranged from 1·36 in spring and summer to 1·84 in autumn, and reproduction was observed throughout the year. Nauplii abundance averaged 28 + 7·4 ind 11, a value much lower than expected for in situ copepod populations and possibly due to behavioural processes such as cannibalism and inhibition of egg deposition. The densest assemblages of splashpool microcrustacea were almost entirely T. californicus, principally mature adults and including clasped male-female pairs and ovigerous females. A simple population growth model is presented, along with parameters for calculating the instantaneous rate of increase, birth, and death in the absence of disturbance.

The population dynamics of Nereis diversicolor (Annelida: Polychaeta) was studied at Stiffkey salt-marshes (north Norfolk coast). Monthly sampling from August 1992 to July 1993, on the lower salt marsh gives a mean annual density of 392 ind m−2 and a biomass of 10·26 g m−2 DW. Cohort analysis was made using ‘Bhatta’ software, allowing the growth and production estimations of the four cohorts. The production was 17·91 g m−2, giving a P:B ratio of 1·8. Nereis diversicolor population has only one recruitment in July.

The reproductive cycle of the pedunculate barnacle Pollicipes pollicipes from two intertidal levels (mid and low) at Cabo de Sines, south-west coast of Portugal has been described. Pollicipes pollicipes larger than 12.5 mm (rostrocarinal distance, RC) are simultaneous hermaphrodites. Minimum size for maturity of the female gonad was 12.5 mm (RC) whilst sperm production is achieved at a smaller size (10 mm). The breeding season was from April to September. Reproductive activity was similar at both tidal levels and was significantly correlated with seawater temperature. Brooding activity was most pronounced in late spring and summer when seawater temperature ranged from 18 to 21°C. Throughout the year, sperm was stored in the seminal vesicles, although the testes regressed from October–December. The female gonad was resting in October–January and active during March–September. During resting, only a few empty ovarioles were observed. At the beginning and in the middle of the reproductive season (March to August), the ovary was completely disrupted after fertilization and ovary recovery occurred simultaneously with egg development. During the end of the reproductive season (September–October), synchrony was retarded as recovery of the ovary was slower than egg development. The pattern of functioning of the female gonad should allow production of several broods during the season.

Studies of the osmotic and ionic responses of the supralittoral rock pool inhabitant Tigriopus brevicornis (Crustacea: Copepoda) showed that this species of orange harpacticoid copepod is an unusually euryhaline osmoconformer. Body fluid osmolalities were 297–3691 mOsm kg−1 over a medium range of 151–3440 mOsm kg−1. Whole body sodium increased from 3·65 to 15·0 μmol Na+ mg DW−1 (dry weight) over the medium range 80–1900 mM Na+. Comparative studies on Artemia nauplii and the prawn Palaemon elegans revealed the characteristic hyper-hyporegulation of both organisms. Body density of T. brevicornis remains greater than that of the external medium over the salinity range 5–100 psu because of changes in body fluid osmolality and body volume. Median body density values for T. brevicornis ranged from 1·0359 g ml−1 in 5 psu (median density of 5psu seawater–1·0017 g ml−1) to 1·0848 g ml−1 in 100 psu (median density of 100 psu seawater=1·0751 g ml−1). Tigriopus brevicornis is principally a benthic forager and needs to remain negatively buoyant over a wide salinity range. Environmental monitoring of five supralittoral rockpools was conducted over a year. Live or dormant T. brevicornis were found in salinities of 4–150 psu; temperatures of −1 to +32°C and oxygen concentrations of 0 to >20 mg l−1. It is probably of advantage to T. brevicornis to be an osmoconformer; it is perhaps energetically efficient for such a small organism (~1 mm) and avoids buoyancy problems at high salinity.

A new species of poecilosclerid sponge from methane seeps on the Louisiana Slope, Gulf of Mexico, USA is described. This thickly encrusting sponge grows around vestimentiferan tubes and has a very patchy distribution. The skeletal structure and the spicule set match those characterizing the genus Ectyomyxilla. The new species, Ectyomyxilla methanophila sp. nov., is distinguished from the remaining species in the genus by the structure of its ectosomal skeleton, where small acanthostyles are never present, and by its choanosomal skeleton, which is barely reticulate and has echinated main tracts. The small size of the choanocyte chambers suggests occurrence of nutritional benefits derived from association with chemoautotrophic symbiotic bacteria. However, the presence of oscules, ostioles, aquiferous canals and choanocyte chambers indicates that this sponge also relies partly on filtration for its nutrition. This is the first record of the genus Ectyomyxilla in the northern hemisphere, and the first non-carnivorous demosponge known to exploit methane-rich marine environments.

The chronometric mechanism of compensation for the apparent movement of the sun was investigated in adult individuals of Talitrus saltator (Amphipoda: Talitridae) from Mediterranean latitudes. The individuals were subjected to alteration of the duration of illumination, while its phase remained the same as in nature. A close relation between photoperiod length and the chronometric mechanism of the sun compass was observed, which could explain the seasonal adaptation of the sun compass. We propose an alternative to the classic hypothesis of daily differential compensation for the apparent movement of the sun.

A new genus is established in Eunicidae: Fauchaldius gen. nov., a symbiont of hexactinellid sponges that has only subacicular hooks, with F. cyrtauloni sp. nov. as its type species. Nine new species are described in Eunice: E. hernandezi sp. nov., E. ibarzabalae sp. nov., E. mikeli sp. nov. and E. nonatoi sp. nov. all belonging to the fuscusbidentate group; E. edwinlinkae sp. nov., E. hartmanae sp. nov., E. lanai sp. nov., and E. miurai sp. nov. all belonging to the flavus-tridentate group; and E. donathi sp. nov. that belongs to the fuscus-unidentate group. Further, two new species are described in Marphysa: M. angeli sp. nov. that is grouped with species having only composite falcigers, and M. orensanzi sp. nov. that belongs to the group with composite falcigers and composite spinigers. A key to identify genera in Eunicidae is included. A key to identify species of Eunice is appended.

All the currently known species of Guitarra with spiny isochelae have been reviewed by SEM: Guitarra fimbriata, Guitarra indica, Guitarra bipocillifea, Guitarra abbotti and Guitarra laplani. A new species from Namibia;Guitarra flamenca, is described, which is characterized by bipocilla-like spiny isochelae similar to those of Tetrapocillon atlanticus, placochelae in two different morphological categories and very robust megascleres. After a revision through SEM of the specimen of Guitarra fimbriata var. indica, it clearly belongs to Guitarra flamenca sp. nov. The morphological variability of the placochelae and the spiny isochelae across the Guitarra-species has been analysed and the main parameters useful to differentiate species are highlighted.

Combining the use of scanning electron microscopy and microcinematography with functional and behavioural observations has clarified many aspects underlying the feeding processes of the small planktonic sergestid shrimp Acetes sibogae australis. In captivity Acetes sibogae australis is an opportunistic feeder that uses four principal feeding modes to capture a wide size range of prey: Artemia nauplii (<0.33 mm), copepods (<1mm) and moribund Acetes (up to 25 mm). Prey capture is effected by combined actions of the first three pairs of pereiopods and the third maxillipeds before transfer to the more dorsal second maxillipeds. The second maxillipeds are the principal appendages used in securing, manipulating, sorting and rejecting prey before insertion into the vicinity of the inner mouthparts.

Food resource partitioning and trends in feeding strategies were examined in 3882 individual decapod crustaceans collected from 1989 to 1990, using bottom trawls at depths between 380 and 2261 m in the Catalan Sea (western Mediterranean). The vertical distribution of available food resources near the bottom was the most important factor responsible for food resource partitioning among bathyal decapod crustaceans by depth stratum and season. Decapods were assigned to five different trophic groups according to the food resource exploited and feeding strategy employed (macroplankton feeders, macroplankton-epibenthic feeders, epibenthic feeders, epibenthic-endobenthic feeders, and deposit feeders). There was little dietary overlap, indicating that species did partition the available resources. Overall, dietary overlap values among species increased with depth. Although a trend to increase H’ values for diets with depth was observed, this was not significant (P < 0.10), whereas differences in the percentage of empty stomachs and the frequency of foraminiferans and pteropods in the foreguts increased significantly (P < 0.05) with depth. This last result is indicative of a progressive increase in the importance of deposit feeding in decapod crustaceans as depth increases.

In the common intertidal sea anemone Actinia equina (Cnidaria: Actiniaria) the morphological plasticity and lack of hard parts has caused considerable debate as to what constitutes a species. Over the last several years genetic studies have indicated that this ‘species’ consists of various separate gene-pools which appear to function as cryptic biological species. Conventional taxonomy has often concentrated on the use of a cnidome, the type, structure and number of nematocysts ('stinging’ cells). However, the usefulness of nematocysts to distinguish among various morphs of A. equina and other anthozoan species has recently been questioned. Here we describe the first detailed study of nematocyst differences between two well characterized genetically differentiated morphs with different coloured pedal discs. Measurements were taken from each type of nematocyst in five different tissues. Contrary to expectations, clear and significant nematocyst differences were found between Actinia with red or pink pedal discs and others with green to grey pedal discs. These findings support previous electrophoretic studies and suggest that quantitative descriptions of the cnidome may accurately identify separate species within other genera of Anthozoa.

A Corophium-bed characterized by a mosaic of emerged areas and tidal pools during low water was established on an intertidal flat in the southern part of the Danish Wadden Sea. In spring 1990, the plateaux harboured relatively high densities of the amphipod Corophium volutator, whereas the amphipods were almost absent in the pools. Following a parasite-induced mass-mortality in the population of Corophium, summer 1990, the plateaux of the bed were subjected to sediment erosion. The heterogeneous plateau-pool structure disappeared, accompanied by increased median particle diameter and decreased silt content in the former plateau sediment. These events were accompanied by increased chlorophyll-a concentrations in the sediment of both plateau and pool areas.

The results suggest Corophium volutator to be the single most important organism stabilizing the plateau sediment, and hence, the heterogeneous topographic structure of the Corophium-bed. It is proposed that the stabilizing effect of Corophium burrows also in deeper sediment strata may outweigh the surface stabilizing influence of epipelic diatoms, as well as the negative effect of amphipods eating the diatoms, in non-cohesive coarser sediments.

It is generally believed that lecithotrophic larvae of annelids do not possess functional excretory organs. However, as in certain annelids the planktotrophic trochophora larva has been secondarily modified into a lecithotrophic developmental stage and because protonephridia are characteristic for the trochophora, lecithotrophic developmental stages should also possess such organs. To test this assumption hatchlings of the orbiniidan Scoloplos armiger, which develops directly without a free-living larval stage, were investigated ultrastrucrurally. Each hatchling possesses a pair of protonephridia which lie caudal to the eyes and almost level with the frontal margin of the foregut. Each organ consists of three multiciliated cells, a terminal cell, a duct cell and a nephropore cell. The terminal cell bears a distally oriented hollow cytoplasmic cylinder, which surrounds the cilia. Adherens junctions connect this structure to the duct cell. Several clefts and pores perforate the wall of the hollow cylinder. Extracellular material covers the pores and clefts and thus may function as a molecular sieve during filtration. A comparison with the protonephridia of other annelid larvae reveals: (1) that one pair of protonephridial head kidneys consisting of a terminal cell, a duct cell and a nephropore cell must be assumed for the trochophore in the ground pattern of annelids and (2) that these organs are preserved when lecithotrophic larval stages evolved within the Annelida