Morphometric analysis is one of the tools widely used to quantify, analyse and describe the variations in the biological forms of animals. In this study, we examined the linear morphometric variations of the shell of the small intertidal gastropod Echinolittorina lineolata and compared the patterns to identify variations among populations and between sexes. The individuals were collected from latitudes 3°S, 14°S, 21°S and 23°S along the Brazilian coast. Traditional morphometric analysis was performed, and the morphometric variables of the shells, namely, the length and width of the shell and the length and width of the shell opening were obtained. The observed size pattern was influenced by latitude, as well as by local spatial responses to factors such as the substrate changing the morphometric variables of the snail. Of the morphometric variables, the length and the width of the shell were the most representative variables that influenced the gastropods in the different latitudes. These variables were also different in males and females, with females having larger shell lengths and widths across all latitudes.

Some Antarctic littorinoideans have a remarkable convergence with Naticoidea in shell and operculum features. Two naticid-like species of that group are studied in their phenotypic features in order to improve their taxonomy and to discuss the meaning of that convergence, as the former are herbivore-detritivore and the latter active predatory organisms. One of the studied species is the littorinid Laevilacunaria antarctica (Martens, 1885). The other belongs to a new genus – Pseudonatica, with the type species also newly described: P. antarctica, the genus is tentatively placed in Zerotulidae. Another Pseudonatica is also described, P. ampullarica, based only on shells collected by Marion-Dufresne French expedition off Brazilian coast, this finding expands the occurrence of zerotulids northwards. Besides the similarities of shell and operculum, other structures of these Antarctic species also show singular similarities with naticoideans, such as the wide foot, the complexity of opercular attachment in pedal opercular pad, the wide oesophageal gland, and the coiled arrangement of the pallial oviduct. The phenotypic characters were coded and inserted in a previous large phylogenetic analysis on Caenogastropoda (Simone, 2011), furnishing a wide basis for discussion on the characters, taxonomic position, evolution and adaptations of these organisms.

Echinolittorina punctata was historically distributed in the southern sectors of the Mediterranean Sea. However, in the last decades a progressive range extension has occurred. In this context, new populations in France (Colliure, Cap d'Agde) and in Italy (Monte Argentario, Tuscany) are reported here. The population in Cap d'Agde is the northernmost in the entire Mediterranean Sea, the population in Monte Argentario is the northernmost along the Italian Tyrrhenian coastline and along the direction of range extension described in the last few years. Details on population density and size frequency distributions in Monte Argentario are provided, showing a decrease in density and an increase in minimum size from south to north. New records are also provided from Salamina Island and Rhodes Island in Greece. The latter likely dates back to 1836–1837 and is the first record from the Mediterranean Sea. This record confirms that the species was widely distributed in the Levantine Sea at the time, although records from Greece and Turkey are extremely rare in the literature and in museum collections.

Living populations of the meso- and supralittoral molluscs Siphonaria pectinata and Echinolittorina punctata are recorded for the Tunisian shores. Siphonaria is most likely to be newly established on this coast, being easily detected and scored as absent in the same sites during previous surveys. The case is unclear for Echinolittorina, for which we do not know any positive published records prior to 1970 but which may have been confused with Melarhaphe neritoides. Both species are of tropical West African affinities and are potentially excellent markers of faunal change in the Mediterranean Sea.