A new genus and species of cheilostome bryozoan associated with hermit crabs in the subantarctic Southwest Atlantic

Abstract

Some bryozoan species occur on gastropod shells occupied by hermit crabs, often dominating the shell surface to the exclusion of other encrusters. Symbioses between bryozoans and pagurid crabs are known from a wide latitudinal range, including tropical, warm- and cold-temperate regions. Here we describe Burdwoodipora paguricola gen. et sp. nov., a cheilostome bryozoan associated with pagurized shells occupied by the hermit crab Pagurus comptus White in subantarctic waters of the Southwest Atlantic. The association seems to be obligate, as the bryozoan was always found enlarging the last whorl of its gastropod substrate. The new species, however, is not species specific with regard to its shell substrate, as it was found to be associated with 31 species of gastropods with helicoidal coiling. Well-developed colonies may project up to 360° from the outer lip of the shell. The chamber built by the bryozoan is usually larger than the whorl that would have been generated by the gastropod. This is one of the few known cases of an obligate association between a bryozoan and a pagurid crab outside the ascophoran family Hippoporidridae and is also the first bryozoan/hermit crab symbiosis documented in the subantarctic region. The inclusion of Burdwoodipora in the Pacificincolidae, a family currently represented by just four species from the Northern Hemisphere, is discussed