Adult females of Strongyloides robustus Chandler, 1942, a parasite of sciurids in North America, were found in the duodenal mucosa of 30 of 32 red squirrels (Tamiasciurus hudsonicus (Erxleben)) collected in Cape Breton Island, Nova Scotia, Canada. The parasitic female is illustrated and redescribed; characteristics include: body 3.8-8.0 mm long, cephalic extremity with X-shaped mouth and 8 circumoral lobes, ovaries spiralling around intestine, and tail bluntly rounded. Eggs in fresh feces contained tadpole-stage larvae. In fecal cultures, eggs hatched and larvae invariably developed to the filariform infective third stage; i.e. a free-living generation did not occur and is probably absent in S. robustus in Cape Breton and possibly other parts of North America. It is hypothesized that homogonically developing S. robustus might be more fecund or more efficiently transmitted than species of Strongyloides that exhibit both homogonic and heterogonic development. Larvae of S. robustus in fecal cultures, i.e. homogonic larvae, are described in detail. Intestinal walls of second- and third-stage larvae, as well as the lateral chords of young third-stage larvae, contained numerous round bodies, likely nutrient stores. Third-stage larvae were present within 2 days in cultures maintained at 30°C, 4 days at 20°C, and 7 days at 15°C. They lived for at least 33 and 30 days at 15° and 20"C, respectively. Third-stage larvae probably die when their nutrient stores are exhausted.
Morphology of adult parasitic hermaphrodites, free-living males and females, rhabditoid and infective larvae of Rhabdias agkistrodonis Sharpilo, 1976 is described. Adult parasites of the species differ from corresponding stage of other Rhabdias species from snakes in the presence of short cuticular needle on the tip of the tail. Free-living generation stages of R. agkistrodonis have typical rhabditoid morphology. Homogonic infective larvae differ from heterogonic ones in the shape of stoma and oesophagus. Three new hosts: Halys viper (Agkistrodon halys) (Pallas) from Altaiskii Krai (Russia), Okinawa habu (Trimeresurus flavoviridis) (Ilallowell)' and T, elegans (Gray) from Okinawa Island (Japan) are added to the host range of R. agkistrodonis known previously exclusively from short-tailed viper (Agkistrodon blomhoffi) from the Russian Far East.