Rediscovery and redescription of Gymnangium sibogae (Billard, 1913) (Cnidaria: Hydrozoa: Aglaopheniidae)

A hydroid, originally described from the Kei Islands, Moluccas, as Halicornaria allmani (sic!) Marktanner var. sibogae Billard, 1913, was recently rediscovered at two additional Indonesian localities. Since it proves morphologically different from its western Atlantic counterpart, Gymnangium allmanii (Marktanner-Turneretscher, 1890), it is confidently raised to species as G. sibogae (Billard, 1913). Its morphological features are fully described and illustrated, and are compared with those of other poorly-known nominal species of the genus, notably G. furcatum (Bale, 1884), G. insigne (Allman, 1876), G. pennatulum (Ellis and Solander, 1786), and G. roretzii (Marktanner-Turneretscher, 1890). A reexamination of the type of G. insigne proved that it is morphologically indistinguishable from G. pennatulum, the latter having priority.