Nematodes from the mantle cavity of Discus cronkhitei, Zonitoides arborea, and Deroceras gracile, and the rectum of Rana spp., Bufo americanus, and Ambystoma jeffersonianum in Ontario are referred tentatively to Cosmocercoides dukae (Holl, 1928), In molluscs, females deposit third-stage larvae that leave the mantle cavity and appear in slime trails left by snails; when placed on the foot of snails these larvae entered the respiratory pore and went to the mantle cavity where they developed. Larvae were found in the genital tract and ovary of slugs and in eggs of both snails and slugs. These penetrated into the mantle cavity of embryo molluscs which subsequently hatched. All stages of C. dukae can survive for long periods in tap water or invertebrate saline. Females sometimes laid eggs which hatched if they contained a first-stage larva and the latter developed to the infective stage. Worms of all stages from molluscs fed to frogs were passed at intervals in the faeces and there was no evidence this species could establish itself in amphibians; the occurrence of cosmocercids in amphibians in Ontario is possibly the result of the latter eating infected molluscs, the worms being able to survive passage through the gut. The larvae and adults are described in detail herein.
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BARTHLLEMY R.I., 1858, Zml., 9, 8
CHABAD A. G., 1958, Idagascar, 12, 159
CHITWOD G., 1937, The Nautilus, 50, 130
1930, J. Pansitol., 17, 61
HOLL F, J, 1928, Sot., 43, 184
OGREN R. E, 1953, Trans. Am. Microsco.Soc. 72., 87, 10.2307/3223367
