Fig. 8d
Sertularia disticha Bosc, 1802: 101, pl. 29, fig. 2.
Type locality. Atlantic Ocean: “...sur le fucus natans...” (Sargassum natans) (Bosc 1802).
Voucher material. Fort Pierce, Fort Pierce Inlet State Park, 27°28’29.5”N, 80°17’25.8”W, on stranded Sargassum sp., 14.vii.2012, 28° C, 35‰, collected manually, one colony, 4 mm high, without gonophores, coll. D.R. Calder, ROMIZ B3966.
Remarks. Hydroids referred to Dynamena disticha (Bosc, 1802) in the western Atlantic occur in two forms, a stunted one (<1 cm high) found on floating Sargassum and a much larger one (up to 5 cm high) on a variety of benthic substrates. It remains to be confirmed whether they are actually conspecific. Specimens observed here, growing on a species of Sargassum, were of the stunted variety as originally described by Bosc (1802).
Comments on the taxonomy of this species have been given earlier (Calder 1991a). Included in the synonymy of D. disticha therein were the following, all originally described from the western North Atlantic: Sertularia exigua Allman, 1877, S. distans Allman, 1877, S. complexa Clarke, 1879, Dynamena bilatteralis Brooks, 1883, Sertularia mayeri Nutting, 1904, S. pourtalesi Nutting, 1904, and with question Dynamena cornicina McCrady, 1859. An extensive list of literature on D. disticha was given in Medel & Vervoort (1998).
Reported distribution. Atlantic coast of Florida. First record.
Western Atlantic. Massachusetts (Nutting 1901, as Sertularia cornicina and S. complexa) to Argentina (Oliveira et al. submitted), including Bermuda (Calder 1991a), the Gulf of Mexico (Calder & Cairns 2009), and the Caribbean Sea (Calder & Kirkendale 2005; Galea 2008). The species has been reported on Sargassum in the Gulf Stream as far north as Nova Scotia (Fraser 1918, as S. cornicina).
Elsewhere. Circumglobal in tropical, subtropical and temperate waters (Peña Cantero & García Carrascosa 2002).