As for many other commercially exploited octopodid species, there are no detailed descriptions of the eggs and hatchlings of Enteroctopus megalocyathus that can be used for the identification of individuals captured in plankton samples. Eggs, clutches and hatchlings are described here for the first time and compared with those of both other Patagonian octopodids and other Enteroctopus species. Relative to other Enteroctopus, hatchlings were large with total length (TL) 14.8–21.5 mm, mantle length (ML) 7–9.5 mm and arm length (AL) representing 90.5% of the mantle. Dorsal chromatophores were more abundant than ventral ones, and their shape and distribution created a very distinctive pattern. Eggs and hatchlings were found to have several characteristics that can be used for species identification. Although the mode of life of newly hatched cephalopods is often categorized as either planktonic or benthic, the hatchlings in aquaria showed no preference for swimming or settling. Additionally, the size of eggs and hatchlings which is correlated with the mode of life at hatching in other octopodid species, fitted both planktonic and benthic in E. megalocyathus. Furthermore, morphological and behavioural characteristics were similar to the pre-settlement stage of planktonic hatchlings of Octopus vulgaris. Therefore, we suggest that hatchlings of E. megalocyathus have an unusual, suprabenthic mode of life.

Tributyltin (TBT) and other pollutants are present in Patagonia, and are associated with maritime traffic and human activities. Cause–effect relationship between TBT and imposex development in females of marine gastropods is well documented. We tested whether the imposex incidence associated with TBT pollution is related to detectable shell-shape variations in the edible marine snail (Buccinanops globulosus). We compared shell shape of B. globulosus in six contiguous sites on a gradient of imposex and maritime traffic, by using geometric morphometric analysis. Our results indicated that the registered differences in shell shape are associated to imposex incidence in the harbour zone where previous works have detected TBT pollution. Gastropods from areas of high maritime traffic presented a rounded shell with a shorter spire, and a smaller relative size of the shell aperture, whereas the opposite shape (fusiform shape, elongated-spired shell and bigger relative size of the shell aperture) occurred in gastropod shells from areas of low maritime traffic. Shell variation registered here could be useful to detect TBT pollution in populations of B. globulosus and another neogastropod species.