Two new species of the genus
Tetraonchus (Monogenea: Tetraonchidae) were found parasitic on the gills of masu salmon,
Oncorhynchus masou cultured in freshwater in Yamanashi Prefecture, Japan. The specific names, T.
awakurai n. sp. and T.
oncorhynchi n. sp. were given to them. T.
awakurai identical with
T. sp. of AWAKURA (1966), resembles
T. sp. 1 of ERGENS (1971) and
T.
gvosdevi (SPASSKY et ROYTMAN, 1960), but differs from the latter two species in the shape of the cirrus.
T. oncorhynchi isdifferent from all other species in the shape of the cirrus.
In adult
T. awakurai, the marginal hooks are usually absent, although they exist in eight pairs initially and juvenile
T. awakurai has their remnants and/or the full marginal hooks. So it is presumed that they disappear during the course of the development of the parasite.
The present species are characterized by the presence of a single intestine and the absence of the vagina. These primitive morphological characteristics indicate that they occupy a particular systematical position in the monogeneans.
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