Fig. 13a
Plumularia gracilis Clarke, 1879: 246, pl. 5, figs. 29, 30 [permanently invalid junior primary homonym of Plumularia gracilis Murray, 1860].
Plumularia clarkei Nutting, 1900: 61, pl. 3, fig. 5 [replacement name for Plumularia gracilis Clarke, 1879].
Halopteris gracilis.— Schuchert, 1997: 110, fig. 39.
Type locality. Cuba: off Havana, 175 fathoms (320 m) (Clarke 1879: 247).
Voucher material. Off St. Lucie Inlet, 27°11.8’N, 79°57.3’W, 87 m, 04.x.1986, Johnson-Sea-Link, J028/JSL 2132, one colony with several cormidia, up to 3.3 cm high, without gonophores, coll. R. Roesch, ROMIZ B1096.
Remarks. This species was originally described as Plumularia gracilis by Clarke (1879). That binomen, a junior primary homonym of Plumularia gracilis Murray, 1860, is permanently invalid (ICZN Art. 57.2). Nutting (1900) proposed Plumularia clarkei as a replacement name for the species, now currently assigned to Halopteris Allman, 1877 as H. clarkei. Nutting provided a new name in the belief that the binomen P. gracilis was preoccupied in works by Blainville (1834: 479) and Lamarck (1836: 167). However, the species referred to as P. gracilis in both of those works, and earlier in Blainville (1830: 443), was originally founded as Aglaophenia gracilis Lamouroux, 1816, and secondary homonymy with Clarke’s (1879) P. gracilis no longer exists. Nutting, and later Stechow (1923), overlooked the more nomenclaturally important primary homonymy of P. gracilis Clarke, 1879 with Murray’s (1860) use of the same binomen for a species from California.
A detailed account of this hydroid (as Halopteris gracilis) is given by Schuchert (1997), whose material included the colonies from Florida examined here (ROMIZ B1096). Halopteris clarkei has been reported infrequently, and it is known only from the warm western North Atlantic. It is immediately distinguished from the sympatric H. diaphana (Heller, 1868) and H. alternata (Nutting, 1900) in having opposite instead of alternate hydrocladia.
Reported distribution. Atlantic coast of Florida. Off St. Lucie Inlet (Schuchert 1997).
Western Atlantic. Continental shelf of Georgia (Wenner et al. 1984) to Cuba (Clarke 1879), and including the southeastern Gulf of Mexico (Calder & Cairns 2009).