Epibiotic sponges on the hairy triton Fusitriton magellanicus in the SW Atlantic Ocean, with the description of Myxilla (Styloptilon) canepai sp nov.

In the present study we identified a total of 26 sponge taxa, to be added to the 4 sponge species previously registered, living epizoically on Fusitriton magellanicus shells, an abundant and frequent gastropod in the shelf-break frontal area of the Argentine Sea, SW Atlantic Ocean. The majority of the recorded sponges were encrusting living specimens of this gastropod, the most frequent ones being Hymedesmia (Stylopus) antarctica (20%), Clathria spp. (18%), Dictyonella spp. (13%) and Tedania spp. (9%) We described one species, Myxilla (Styloptilon) canepai sp. nov., and extended the distribution of Clathria (Microciona) antarctica and Stelodoryx cribrigera northwards. We also registered, for the second time after its description, the species Stelodoryx argentinae. Considering that the study area is a soft bottom and the only available substrates for settlement of sessile species are either external mineralized skeletons of living organisms, empty shells or crustacean carapaces, we conclude that shells of the gastropod F. magellanicus play a very important role for settlement of sponge species in the area. Moreover, possibly only living F. magellanicus (not the empty or pagurized shells) are important as a settlement substrate because the few specimens found in empty shells could be considered as rare occurrences.