New tissue-dwelling species of Philometra Costa, 1845 and Philometroides Yamaguti, 1935 (Nematoda: Philometridae) from marine perciform fishes off the northern coast of Australia

Based on light and scanning electron microscopical studies, three new species of philometrids (Nematoda: Philometridae) are described from females collected in marine perciform fishes off the northern coast of Australia: Philometra gracilis n. sp. and Philometroides branchiarum n. sp. from tissues behind the gills and gill arches, respectively, of the John's snapper Lutjanus johnii (Bloch) (Lutjanidae), and Philometroides stomachicus n. sp. from the stomach wall of the blackspotted croaker Protonibea diacanthus (Lacepede) (Sciaenidae). Philometra gracilis differs from other congeners described from the Lutjanidae mainly in the presence of large caudal projections, short gravid females (28-42 mm long), the oesophageal gland extending anteriorly far anterior to the level of the nerve-ring, the site in the host and its geographical distribution. Philometroides branchiarum is mainly characterised by the possession of conspicuous, sclerotised oesophageal teeth and very short gravid females (6-8 mm long), whereas P. stomachicus can be differentiated by the body length of gravid females (85-90 mm), the length of the oesophagus (2.67 mm) representing 3% of the body length, the maximum width/body length ratio of gravid females (1: 28-32), cuticular bosses densely distributed throughout the body but absent from the oesophageal region, the absence of oesophageal teeth and caudal projections, and the site in the host. The presence of P. gracilis and P. branchiarum in L. johnii and that of P. stomachicus in P. diacanthus confirm the possibility of the coexistence of more philometrid species in different sites within sympatric specimens of one and the same definitive host.