Biology and description of Antisabia juliae sp. nov., new hipponicid gastropod commensal on Turbo spp. in Laing Island (Papua New Guinea)

The gastropod family Hipponicidae comprises widely distributed but poorly known sedentary species. On the beach-rock of the coral reefs of Laing Island (Papua New Guinea) live rich populations of several gastropod Turbo species of which many specimens have attached to their shell a hipponicid gastropod attributed to a new species, Antisabia juliae. This new species, described in this paper, appears to have adapted its mode of life on live turbinids in several ways resulting in morphological changes (thin basal plate loosely adherent to the supporting shell, functional eyes, very long snout, functional radula, small osphradium) and ethological changes (foraging behaviour: it appears to feed on the epiphytic community growing on the host, in the vicinity of the "host" shell). Except for these characteristics, the mode of life appears quite similar to that of other hipponicid species with few big females surrounded by several much smaller males. Development occurs within the egg mass inside the female shell and a few young snails escape at the crawling stage.