Female morphology of Philometra parasiluri [Nematoda, Philometridae], an ocular parasite of the Amur catfish Silurus asotus in Japan

The female morphology of the nematode Philometra parasiluri Yamaguti, 1935 (Philometridae) is described based on a sub-gravid specimen found in the oculo-orbit of the Amur catfish Silurus asotus Linnaeus of Lake Biwa, Honshu, Japan collected in April 2007. Light and scanning electron microscopical examination made it possible to study in detail the morphology of this so far little-known species. In contrast to the original species description, no cuticular bosses are found on the body surface; in addition to the previously reported eight large cephalic papillae of the external circle, the cephalic end also bears six (2 lateral and 4 submedian) small papillae of the internal circle and a pair of inconspicuous amphids; no oesophageal teeth are present and the anterior oesophageal lobes are slightly elevated; two large, lateral, papilla-like caudal projections are present. To date P. parasiluri has been found only in Japan and the present finding represents the third documented record of this species. Philometra parasiluri probably has a pronounced annual maturation cycle with the period of the production of larvae in the late spring and summer.