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

Abstract

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

Keywords:

• invertebrates
• marine biology
• natural history
• taxonomy
• zoology

Geolocation information

Similiclava nivea. ROMIZ B4021 (point): 49°34’4”N, 123°48’14”W; ROMIZ B4022 (point): 49°34’4”N, 123°48’14”W; ROMIZ B4023 (point): 50°40’3”N, 126°0’33”W; ROMIZ B4024 (point): 49°45’5”N, 124°13’25”W; ROMIZ B4025 (point): 49°34’4”N, 123°48’14”W.

Acknowledgements

We are grateful to Andy Lamb, and to Donna and Charlie Gibbs, for providing access to their large database on the white hydroid (as Clava sp.). Marc Chamberlain provided the northernmost sighting of the species, at the Inian Islands, southeast Alaska. Rick Harbo, Jan Kocian, Janna Nichols and Pauline Ridings also provided sighting records. Particular thanks are due to Oliver Haddrath of the ROM for help with the molecular analysis. Thanks are also due to Kristen Choffe and Maureen Zubowski of the ROM, for assistance in the Laboratory of Molecular Systematics and in the Invertebrate Zoology Section, respectively. Christina Piotrowski and Elizabeth Kools of the California Academy of Sciences provided a loan of a hydroid species from Alaska (CAS:IZ:13160) that we compared with our material. Sandra Millen confirmed that the nudibranch Flabellina japonica preys on Similiclava nivea.