Gonad-infecting philometrid Philometra philippinensis sp. nov. (Nematoda, Philometridae) from the bigeye barracuda Sphyraena forsteri Cuvier (Sphyraenidae) off Mariveles, Bataan Province, Philippine archipelago.

We conducted a parasitological study to identify nematodes infecting the gonads of bigeye barracuda Sphyraena forsteri Cuvier (Sphyraenidae) caught in the West Philippine Sea, off the Mariveles coast, Bataan Province, the Philippine archipelago. Males and very tiny nongravid female philometrid nematodes were collected from the ovaries of the fish. Based on light and scanning electron microscope observations, and supported by molecular analyses of the partial nucleotide sequences of the 18S small subunit ribosomal DNA, the philometrid nematode was determined to be a new species belonging to the genus Philometra Costa, 1845 in the family Philometridae (Nematoda: Dracunculoidea), and was named P. philippinensis sp. nov. This new species was clearly distinguishable morphologically from other congeners that parasitize the gonads of marine fishes. Males have unique sickle-shaped spicules and gubernaculum, and a vulva-like cloacal opening. Following Dentirumai philippinensis Quiazon et Moravec, 2013 and Philometra robusta Moravec, Möller et Heeger, 1992, this is the third philometrid species and the first gonad-infecting philometrid from the Philippine archipelago.