The life cycle ofPlagiorchis spec. 1, a species of thePlagiorchis elegans group (Trematoda, Plagiorchiidae)

Abstract

The life cycle was investigated of a trematode of the genusPlagiorchis, named provisionallyPlagiorchis spec. 1. Cercariae were obtained from the fresh-water snailLymnaea stagnalis L. from two localities remote from each other: the Roggenburg fish-ponds near Ulm, Federal Republic of Germany, and the “Obedska bara” nature reserve near Belgrade, Yugoslavia. Material from the two trematode populations was used separately for infection experiments and compared, to show the constancy of the morphological features of the developmental stages. Experimental second intermediate hosts were larvae of Ephemeroptera (Cloëon), Trichoptera, Zygoptera, Nematocera (Chaoborus, Culex-type, Chironomidae), Dytiscidae, and to a lesser degreeAsellus aquaticus. Chickens were fed with infested larvae and adult trematodes were recovered from the intestine. The first trematode eggs appeared in the faeces after 6–8 days. They matured within 30–50 days at room temperature. Laboratory-rearedLymnaea stagnalis from two age groups (3.5 months and 2 years) 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 fresh-water snails were tested as possible first intermediate hosts by feeding them mature eggs. In oneGalba palustris Müll. the trematode investigated developed up to the cercarial stage, whereas experiments withRadix auricularia L.,R. peregra Müll. andPlanorbarius corneus L. were negative. The cercaria is a Xiphidiocercaria armata with seven penetration glands on one side and eight on the other. Its chaetotaxy is elaborated. The metacercaria 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 thePlagiorchis elegans group compiled by Krasnolobova. According to the life cycle, the investigated species mostly corresponds withPlagiorchis laricola as described by Ždárská andP. elegans as described by Styczyńska-Jurewicz and Samnaliev et al. There are differences and contradictory data in the literature on these species, which do not allow an exact determination until further knowledge about related forms is available.