Oxygen microenvironments adjacent to mussel (Mytilus edulis) and periwinkle (Littorina littorea) tissues were described using micro-optodes. For mussels these environments did not differ from the surrounding water body in either static or stirred conditions. Consequently no difference was seen in the MO2 of mussels within stirred and unstirred respirometers. An oxygen extraction efficiency of 30% was recorded for mussels in stirred and unstirred conditions. Under static conditions, periwinkles, with their weak ventilatory arrangements, were not capable of ventilating the surrounding water efficiently, and their tissues were surrounded by hypoxic seawater, even in fully aerated water. The resultant build up of oxygen gradients close to the tissue surface led to measures of oxygen consumption representative of hypoxic conditions in fully aerated, unstirred respirometers. Stirring of the contents of the respirometer immediately prior to final oxygen concentration measures was insufficient to counter this effect, which could only be avoided by continuous artificial stirring of the respirometric chamber water. These findings have considerable implications for study of the oxygen consumption of aquatic animals with limited ventilatory capacity, such as gastropod molluscs.

Two new species of dorid nudibranchs of the genus Tambja are described from the Indo-Pacific and the temperate waters of the western Atlantic. Tambja haidari sp. nov. is only known from the type locality in Senegal. This species has dark blue ground colour with yellow bands and sky-blue spots, which become real tubercles along the tail. The internal features are typical of species of the genus, with rachidian teeth that lack denticles and with a prostate slightly differentiated from the rest of the vas deferens. Tambja blacki sp. nov., from Papua New Guinea and eastern Australia, has yellow-green or green colour with black blotches. There are two large blotches on the head continuing from the inner side of the base of the rhinophores towards the rear. The notal margin is elevated and joins behind the gill in a well-developed hump. The reproductive system of this species is very characteristic because it has some features more typical of species of Nembrotha than of Tambja (i.e. vaginal gland absent, prostate spread over the bursa copulatrix and wide and elongate vagina). These descriptions bring the number of species of Tambja found around the world to 31.

A new species of Thyasiridae, ‘Leptaxinus’ indusarium sp. nov. is described from the Indus margin, off Pakistan. The generic affinity is tentative and possible alternatives are discussed. It occurs between 800 m and 1000 m water depth in a low oxygen environment, where it is relatively abundant. The ecological setting is described and data suggest that this species is not chemosymbiotic.

The mussel Perumytilus purpuratus is distributed from Ecuador to the Strait of Magellan on the Pacific coast; and also extends along the Atlantic coast up to La Lobería, Argentina. The species forms dense three-dimensional matrices which constitute a microhabitat for a wide variety of organisms. Here we test the hypothesis that factors determining habitat structural complexity and environmental heterogeneity of Perumytilus matrices have significant effects on the associated macrofaunal community. In total we found 92 invertebrate taxa in P. purpuratus matrices. The number of layers (stratification) in the matrix had a significant effect on evenness: the greater the stratification, the lower the evenness index. Sediment retention by matrices in sheltered sectors had a significant effect on evenness: greater sediment retention resulted in lower evenness. Sediment retention also determined significant differences in macrofaunal assemblages. In matrices without sediment retention, mussel layering and the presence of algae on the shells of P. purpuratus determined significant macrofaunal differences. As a dominant competitor, P. purpuratus plays a major role in intertidal rocky shores where it is present, structuring communities and determining local biodiversity.

Calliopaea bellula, a sacoglossan opisthobranch, was recently found in the Ria Formosa, a coastal lagoon in southern Portugal feeding upon eggs of the cephalaspidean opisthobranch Haminoea orbignyana, the second most abundant gastropod inhabiting the sea grass habitats in the lagoon. The feeding behaviour of C. bellula is described together with photographic images of this process. Egg-masses of other common opisthobranch species collected in the Ria Formosa were also offered, but they were always rejected. This is the first known case of predation on eggs of H. orbignyana.

Gonad of the Mediterranean pectinid Flexopecten glaber was studied in order to describe the morphology and the ultrastructural characteristics of the mature spermatozoa. The spermatozoon has a 2.5 μm pyriform head and a 40–45 μm flagellum. The four mitochondria of the mid-piece are 0.6 μm in diameter. The nucleus contains dense chromatin fibres and possesses two depressions: a wide (0.19 μm) and deep (0.58 μm) sub-acrosomal one, and the other at the base of the head, less deep (0.36 μm) and less wide (0.12 μm). The objective was to situate this scallop in the phylogenetic diagrams found in the literature concerning the commercial pectinid species.

The diet of Sepia officinalis was studied by examining the stomach contents of 522 specimens caught off the coast of the Algarve, Portugal. A total of 49 different prey items, belonging to six taxa (Polychaeta, Cephalopoda, Teleostei, Bivalvia, Crustacea and Gastropoda) was found, indicating opportunistic feeding behaviour. The diet was examined in relation to season, sex and size. The diet of males and females were similar. For small S. officinalis, crustaceans were more important in weight, whereas for larger specimens, fish were dominant. Seasonal differences in the diet were apparent but were shown to be possibly influenced by the cuttlefish size.

Stomach contents and carbon (C) and nitrogen (N) stable isotope analysis were used to evaluate trophic relationships of jumbo squid, Dosidicus gigas. Buccal masses, beaks and stomach contents of large and medium maturing-sized jumbo squid and muscle from its main prey, the myctophid Benthosema panamense, were collected in the Gulf of California, Mexico during 1996, 1997 and 1999. Both the quantified C and N-isotope ratios in muscle, and stomach content analysis revealed that larger-sized maturing squid showed a higher trophic position than medium-sized individuals. However, a discrepancy between stomach contents versus stable isotope analyses was found in evaluating trophic relationships. Simple dilution models as a function of growth were used to estimate the C and N renewal dietary shift for jumbo squid. Estimates of the initial C and N pools in D. gigas with an initial age of 70 days and 210 days indicated isotopic shifts of 32% after a threefold biomass increase and 25% after a fourfold biomass increase, respectively. Additionally, beak samples of jumbo squid were evaluated as an alternative tissue to estimate squid trophic position using stable isotopes. The results showed a significant correlation between stable isotope ratios from muscle and beak samples. Muscle isotope values were higher than beak by 1% and 4% for δ13C and δ15N respectively. A test with jumbo squid beaks collected from a stomach of a stranded sperm whale confirmed the viability of this method.

The number and distribution of ampullary pores present on the blackmouth catshark, Galeus melastomus and the velvet belly dogfish, Etmopterus spinax do not differ with the size/maturity or gender of the specimen and were found to be related to prey preference.