Alcyonidium polyoum (Hassall, 1841) Bryozoaire Ctenostome

Porter, John S. Ryland Joanne S., 2003, The identity of Alcyonidium gelatinosum (Linnaeus, 1761) (Bryozoa: Ctenostomatida), Journal of Natural History 37, pp. 2179-2189 : 2183-2184

Alcyonidium polyoum

Hassall (1841c) described Sarcochitum polyoum (named for the large numbers of ova) as ‘with twenty tentacula ... investing Fucus serratus ’. He omitted to give a locality, but mentioned that S. polyoum and Cycloum papillosum (i.e. A. hirsutum ) ‘are often so mixed up in their distribution on the same piece of seaweed, that it requires a practised eye to distinguish them’. Presumably, then, they came from the

same place. The locality for C. papillosum was Dublin Bay, a coast with only a restricted occurrence of Fucus -covered shores. In the Catalogue of Irish Zoophytes (Hassall, 1841a, 1841b) the localities of Merrion and Black Rock are frequently mentioned. Whilst Merrion is sandy, there is extensive hard substratum at Black Rock (Irish grid O 225293), which we were able to visit on 20 July 2001. The shore is a rocky reef of bedrock and boulders to the west of a slipway at Seapoint; it tapers seawards so that it is broadly triangular in shape. The middle shore is covered with clean, shortish Ascophyllum , suggesting only moderate shelter derived from the shape of Dublin Bay and the extensive western breakwater of Dun Laoghaire harbour. The lower shore comprised mixed fucoids, and the Fucus serratus supported both A. hirsutum and A. polyoum in reasonable abundance. The A. polyoum colonies were thin, and not extensive; many of them had conspicuous oocytes and/or embryos. As there were no very small colonies, there had been no settlement during winter (which would have indicated the presence of A. gelatinosum ), and larval release from A. polyoum had evidently not yet started. Black Rock seems as close to the type locality of A. polyoum as can reasonably be determined. We have accordingly placed some of this material, as topotypes of A. polyoum (Hassall, 1841c) , in The Natural History Museum, London, registered numbers 2002.2.1.2. In the circumstances, in accordance with Art. 75 in the Code of Zoological Nomenclature (International Commission on Zoological Nomenclature, 1999), we have selected one of the gravid colonies as a neotype (2002.2.1.2). It should be noted that the name polyoum has remained in use in France (e.g. d’Hondt and Goyffon, 1989, 1991; d’Hondt, 1996) and has been restored in current publications (Ryland, 2002a, 2002b; Ryland et al., 2002).