New records, taxonomic notes, descriptions and redescriptions of some uncommon thecate hydroids (Cnidaria: Hydrozoa: Leptothecata)

Abstract: The present report provides new records, taxonomic notes, descriptions and redescriptions of several species of lesser-known thecate hydroids. Five species belong to the family Sertularellidae Maronna et al., 2016, one to the Syntheciidae Marktanner-Turneretscher, 1890, and one to the Aglaopheniidae Marktanner-Turneretscher, 1890. Type material of Sertularella conica Allman, 1877 was re-examined, and a modern redescription is provided, together with notes on its problematic synonymy that now includes S. gayi unituba Calder, 1991. Fertile specimens of S. inconstans Billard, 1919 are rediscovered, and its synonymy is broadened through the inclusion of S. natalensis Millard, 1968. A new species, S. malagasiensis sp. nov., is described from the south of Madagascar. Sertularia exigua/laxa Allman, 1888, a hydroid assignable to the genus Sertularella Gray, 1848, is found to have both primary and secondary homonyms; its taxonomy is discussed, and the replacement name S. mutatnomen nom. nov. is introduced for it. Sertularella pellucida Jäderholm, 1907 is recorded for the first time from the Mid-Atlantic Ridge, outside its previously-known main area of occurrence, in the Arctic Ocean. The sexually-dimorphic gonothecae of Synthecium brucei Vervoort & Watson, 2003 are described for the first time. Halicornaria setosa Armstrong, 1879 is rediscovered in material from the Red Sea, and the binomen is removed from the synonymy of Taxella eximia Allman, 1874, while transferring it to the genus Taxella Allman, 1874, as T. setosa comb. nov., on the account of its gonothecae not protected by phylactocarps.