Similiclava nivea (Cnidaria: Hydrozoa: Similiclavidae): a new family,genus and species of athecate hydroid from the Pacific coast of North America

The hydroid Similiclava nivea, gen. nov., sp. nov., is described from colonies collected in nearshore waters of southern British Columbia, Canada. It has been observed by divers, and recorded as Clava sp., several hundred times at locations between southeast Alaska and southern Oregon, USA. While resembling the hydractiniid Clava multicornis, tentacles of S. nivea are arranged in two close whorls in extended hydranths rather than being scattered over the distal end of the hydranth. Moreover, the hypostome is dome-shaped to flattened instead of being proboscidiform. Similiclava nivea also resembles species of the hydractiniid genera Stylactaria, Hydractinia and Podocoryna, but differs in being monomorphic, in lacking spines on the hydrorhiza and in having numerous (as many as 50 or more) sporosacs borne in a broad whorl below the tentacles on normal hydranths. Molecular analysis using the mitochondrial 16S gene sequences reveals that S. nivea is closer to Clathrozoellidae than to Hydractiniidae, although it is clearly distinct from both. A new family, Similiclavidae, is established to accommodate the species. Hydroids of S. nivea were observed at relatively shallow depths (10–30 m) on rocks and epibiota attached to rocky substrates. Colonies are conspicuous because of the relatively large surface area they occupy (up to 20 cm across, and in aggregations often exceeding 100 or more hydranths) together with the height (about 15 mm high when extended) and striking white colour of living hydranths. The cnidome consists of desmonemes, microbasic euryteles and microbasic mastigophores. A substrate generalist observed on rocks, algae, sponges, barnacles, bryozoans and other hydroids in cold-temperate waters, S. nivea is most prevalent in shallow subtidal areas swept by tidal currents.

http://zoobank.org/urn:lsid:zoobank.org:pub:2691E02E-7E14-4820-8D91-41D9E7E8BF62