THE LIFE-CYCLE OF PLAGIORCHIS-SPEC 1, A SPECIES OF THE PLAGIORCHIS-ELEGANS GROUP (TREMATODA, PLAGIORCHIIDAE)

The life cycle was investigated of a trematode of the genus Plagiorchis, named provisionally Plagiorchis sp. 1. Cercariae were obtained from the freshwater snail Lymnaea stagnalis L. from 2 localities remote from each other: the Roggenburg fish-ponds near Ulm, West Germany, and the Obedska bara nature reserve near Belgrade, Yugoslavia. Material from the 2 trematode populations was used separately for infection experiments and compared, to show the constancy of the morphological features of the developmental stages. Experimental 2nd intermediate hosts were larvae of Ephemeroptera (Cloeon), Trichoptera, Zygoptera, Nematocera (Chaoborus, Culex-type, Chironomidae), Dytiscidae and to a lesser degree Asellus aquaticus. Chickens were fed with infested larvae and adult trematodes were recovered from the intestine. The 1st trematode eggs appeared in the feces after 6-8 days. They matured within 30-50 days at room temperature. Laboratory-reared L. stagnalis from 2 age groups (3.5 mo. and 2 yr) were fed mature eggs. Both age groups became infected by eggs of the Roggenburg population. Cercariae emerged after 44-54 days (room temperature) and were identical with those from the natural habitat. Further freshwater snails were tested as possible 1st intermediate hosts by feeding them mature eggs. In 1 Galba palustris Muell. the trematode investigated developed up to the cercarial stage; experiments with Radix auricularia L., R. peregra Muell. and Planorbarius corneus L. were negative. The cercaria is a Xiphidiocercaria armata with 7 penetration glands on 1 side and 8 on the other. Its chaetotaxy is elaborated. The matacercaria is characterized by hardly any growth in the encysted stage and an active process of excystation. The morphology and biology of all developmental stages and the chaetotaxy of the cercariae were identical in both populations. The adults resemble several species in the Plagiorchis elegans group compiled by Krasnolobova. According to the life cycle, the investigated species mostly corresponds with P. laricola as described by Zdarska and P. elegans as described by Styczynska-Jurewicz and Samnaliev et al. The literature on these species contains differences and contradictory data which prevent exact determination until more is known about related forms.