Members of the bryozoan family Hippoporidridae have frequently been found encrusting gastropod shells inhabited by hermit crabs, with which they appear to enter into a symbiotic relationship-shells occupied by hermits may in some species have a tubular extension of the encrusting bryozoan from the shell opening, induced by the presence of the crab. Such colony growth is characteristic of some species of Hippoporidra Canu and Bassler and Odontoporella Héjjas. The type species of Odontoporella, O. adpressa (Busk), has been attributed a nominal distribution from Chiloe Island, Chile (the type locality), to the Falkland Islands, New Zealand, and New Caledonia. In New Zealand, colonies are relatively easily obtainable from some localities, so a study was undertaken to ascertain substratum and morphometric relationships across the range of distribution of the species, using museum specimens and, where possible, fresh material. It became clear that the New Zealand population constitutes a separate species, here named O. bishopi n. sp., in which the orifice is proportionately larger than in O. adpressa. In contrast to O. adpressa, which settles on a range of substrata, O. bishopi preferentially settles on gastropod shells occupied by hermit crabs (mostly Paguristes setosus (H. Milne Edwards)) and shows sexual dimorphism at the level of the polypide. Male polypides not only have modified lophophores but also reduced guts.