New data on the morphology of Philonema oncorhynchi Kuitunen-Ekbaum, 1933 (Nematoda: Dracunculoidea) from the abdominal cavity of Pacific salmon (Oncorhynchus spp.)

The dracunculoid nematode Philonema oncorhynchi Kuitunen-Ekbaum, 1933 is redescribed from specimens collected from three species of anadromous Pacific salmon, i.e. Oncorhynchus keta (Walbaum), O. kisutch (Walbaum) and O. nerka (Walbaum), from Japan, North Pacific Ocean and eastern Russia (Kamchatka), respectively. Scanning electron microscopy revealed the presence of hitherto undescribed cuticular ornamentations on the male caudal end and made it possible to establish the numbers, distribution and shape of cephalic and caudal papillae in the male, which are hardly visible under a light microscope; two horn-like protrusions and a median pre-anal papilla situated on the anterior cloacal lip were not previously described in this species. The necessity of detailed morphological studies on Philonema spp. parasitic in salmonids for the clarification of their taxonomy is stressed.