Analysis of mitochondrial (16S) and nuclear (H3) gene data using phylogenetic and population genetic approaches has revealed some genetic differences between two putative species of western Atlantic Dondice opisthobranchs that feed differentially on hydroids or on up-side-down jellies of the genus Cassiopeia. These results partially support the validity of the species Dondice parguerensis, which was described for the jelly-eating Dondice. However, phylogenetic analyses revealed that the hydroid-feeding species Dondice occidentalis and D. parguerensis are not reciprocally monophyletic and they are identical for the nuclear H3 gene. Although there are morphological and developmental differences between these two nominal species, the molecular data are inconclusive. A possible explanation is that the two putative species are in the process of speciation due to different feeding habits, resulting in the presence of genetic synapomorphies in D. parguerensis, but only in the more variable 16S gene. Because the ranges D. occidentalis and D. parguerensis overlap and there are no obvious barriers to gene flow between the two putative species, this may constitute a possible example of incipient sympatric speciation in benthic marine organisms.

The effects of winter flooding on the intertidal macrobenthic assemblages in the Guadiana estuary were studied by analysing several ecological parameters (abundance, biomass, species richness, diversity, degree of dominance of annelids and deposit-feeders species and number of predator species) as well as changes in the composition of the assemblages. Significant and systematic differences were found in the values of the ecological parameters, especially between winter and summer. We found a significant interaction between the factors ‘time’ and ‘site’, attributable to changes in abundance and composition of the assemblages. The assemblages showed a predominance of some opportunist species in most of the estuary after the flooding, suggesting that these species benefited from the new environmental conditions. Conversely, the assemblages in the mouth of the estuary were severely affected as was shown by the negative changes in biomass, species richness and diversity. These converse responses of the intertidal estuarine assemblages represent effects of flooding different from both catastrophic and negative effects on macrofaunal assemblages.

Sipunculans represent a discrete component of the coral reef ecosystem, since they live inside the calcareous structure. They are an important component in terms of biomass and number of organisms. The present study describes the diversity of sipunculans living inside massive coral skeletons. A total of 43 blocks of dead coral skeletons from Montastraea cavernosa, Montastraea annularis and Diploria strigosa were collected from nearby coral reef areas off Santa Marta, on the Colombian Caribbean coast. Using hammer and chisel, blocks of approximately 1 dm3 were broken into small pieces, from which the sipunculans were extracted. A total of 381 organisms were obtained from the coral blocks comprising four families and 10 species. All the species found have been widely reported in different studies from the Caribbean region. Aspidosiphon fischeri and Phascolosoma perlucens were the two most abundant species comprising more than 60% of the total organisms with a mean density of 18.52 ± 4.64 organisms dm−3. Dead coral substrate from M. cavernosa had the greatest abundance (N = 148), followed by D. strigosa (N = 121) and M. annularis (N = 112). There were no significant differences in the abundance, richness, and diversity of sipunculans between coral skeletons; and within samples there was high variability suggesting that the skeletal substrates analysed came from coral skeletons of different unknown ages of succession. These results describe the sipunculan community structure that live inside three important massive coral skeletons, and contributes to the knowledge of the cryptobiota diversity of the Santa Marta area of Colombia.

Reproductive characteristics of poorly studied hyperiid amphipods, especially Phronimella elongata, are described. Among nine species of hand-collected phronimids, females of Phronimella elongata, Phronima dunbari and Phronima sedentaria cohabited with their young in a ‘barrel' derived from gelatinous zooplankton. Five growth stages of young were identified in Phronimella elongata: young of stages I–IV were found with the mother in the barrel, but stage-V young clinged to the mother retaining no barrel. The cohabiting young in Phronimella elongata and Phronima sedentaria always consisted of single growth stage. In a single female of Phronima dunbari, however, two different stages of young coexisted in a barrel. In Phronimella elongata, the mother size significantly correlated with the number of brooded eggs or cohabiting young regardless of growth stages of young. Considerable variation in the number of eggs or young per female among phronimid species may attribute to the differences in the volumes of the brood pouches.

The digestive system of 36 paralarvae and 150 juvenile Dosidicus gigas were analysed to determine the diet. The early life stages were collected in the central and south region of the Gulf of California during different years and ranged in dorsal mantle length (ML) from 2.8 to 120.5 mm. The food content was separated first into identifiable material (IM) and non-identifiable material (NIM). All paralarvae contained only NIM stored mainly in the caecum rather than stomach. Juvenile squid feed on nine different prey types: euphausiids, copepods, amphipods, unidentified crustaceans, fishes, cephalopods, pteropods, bivalves and polychaetes. The IM were found mainly in the stomachs of juveniles with increasing number and diversity of prey in a function of increasing squid body size. In fact, juveniles from 60 to 120 mm ML had high stomach fullness percentages in half full and completely full stomachs suggesting improvement of swimming and hunting behaviour as they grow.

The abundance and distribution of coastal cephalopods are strongly influenced by the environmental conditions. This study evaluates the seasonal distribution and density of Octopus tehuelchus in three intertidal environments of San Matías Gulf (Patagonia). To estimate and compare density and distribution, monthly transects were carried out, and analysed in relation to the coastlines obtained with satellite images. Densities of O. tehuelchus ranged between 0 and 34 individuals per transect (0–0.11 octopus m−2), and varied between sites. Islote Lobos (IL) had the highest densities (mean octopus per transect 7.32 ± 1.16) followed by El Fuerte (EF) (5.55 ± 0.94) and San Antonio Bay (SAB) (3.40 ± 0.85). Within each site, octopus densities varied between seasons. The highest densities were observed during warm months (SAB = 5.96, EF = 9.52, IL = 14.15) and the lowest during cold ones (SAB = 1.45, EF = 2.6, IL = 3.32). Octopus tehuelchus showed an aggregated spatial distribution, and the nearest neighbour value varied between 0.21 and 0.83 in SAB, 0.27 and 0.78 in EF and 0.23 and 0.53 in IL. Considering the coast lines, the distribution pattern along the intertidal varied seasonally. During warm months this species is widely distributed throughout the intertidal, from the low-tide line to 300 m (in SAB), 500 m (in EL) and 200 m (in IL). On the contrary, during cold months most individuals were found near the low-tide line. These results may be associated with the availability of shelter in the intertidal and the activity and physiology of this species.

The stomach contents of a male sperm whale, Physeter macrocephalus, stranded on Forte dei Marmi beach (Italy, Ligurian Sea) were examined. Food items consisted exclusively of cephalopod hard parts: 233 upper and 291 lower beaks and one fish eye lens. The majority of the identified cephalopod beaks belonged to Histioteuthis bonnellii, but a few beaks of Galiteuthis armata and Octopoteuthis sp. were also found. A new beak size–cephalopod size regression was created for H. bonnellii with specimens caught in the study area. Reconstructed prey weight for the species was much higher when applying this new regression instead of Clarke's, highlighting the need for area- and species-specific regressions for dietary studies. Our analysis represents the second report on the stomach contents of sperm whales from the Mediterranean and the first available information for the Western basin.

The new species Echinofabricia rousei is described for the Mediterranean Sea based on specimens collected along the Sardinia Coast (Porto Conte). The genus Echinofabricia is reported for the first time in the Mediterranean area. At present three species are described within the genus: E. goodhartzorum, described from the Caribbean, E. dubia, described from the East Pacific (Hawaii) and E. alata from Australia.