HETERAKIS FIELDING N-SP (NEMATODA, HETERAKOIDEA) FROM THE AUSTRALIAN WATER-RAT, WITH A REVIEW OF HETERAKIDS OCCURRING IN MAMMALS

Heterakis fielding n. sp. is described from Hydromys chrysogaster. It can be distinguished from Heterakis spumosa, the species it most close ly resembles, in that both males and females are much smaller (4.4 and 5.1 mm, versus 9 and 13 mm, respectively for Australian specimens) an d males have shorter tails (178 versus 345 mu m) with 9 pairs of cauda l papillae compared with 10 pairs for H. spumosa. Of the species of He terakis previously described from mammals three, H. spalacis, H. macro spiculum and H. verrucosa, are presently considered incertae sedis, a fourth has been referred to the genus Gireterakis and a fifth, H. pand ei, described almost simultaneously with H. yamaguti, is considered to be synonymous with it. The remaining species are H. spumosa, H. ingli si and H. yamaguti. The presence of these four species in mammalian ho sts, when all other representatives of the genus occur in grain-eating birds, cannot be explained at present.