sp. nov., a new species of Antarctic ctenostome bryozoan with a key to all Antarctic species of the genus.

Unlabelled: Recent surveys of Antarctic waters in the Terra Nova Bay (Ross Sea) revealed numerous bryozoan species including ctenostome bryozoans. Whereas cheilostome bryozoans are well-studied in these latitudes, ctenostomes remain highly neglected. Large ctenostomes are easily recognized by their lack of calcified skeletons, but this lack also renders them difficult and tedious to identify. As a result, histology and reconstructions of internal soft tissues are required to classify this group of bryozoans. Thanks to the availability of new specimens from Terra Nova Bay, a detailed analysis of growth form, gut morphology and tentacle number of two colonies, initially ascribed to the ctenostome bryozoan genus Lamouroux, 1813, turned out to be a new species, sp. nov., which we described in this study. These specimens were also barcoded (COI) and sequences compared to available ones. Together with the new species described here, a total of ten species of is now known for the Southern Ocean, accounting for one eighth of the entire genus diversity. All Southern Ocean species appear to be endemic. In order to speed the identification of the Antarctic species, we provide an identification key and a distribution map of all type species. In brief, colony morphology, zooidal size and, in particular tentacle number represent the most suitable characters for identifying species within this genus.

Supplementary Information: The online version contains supplementary material available at 10.1007/s13127-023-00629-4.