The life-cycle of Echinostoma miyagawai, a Eurasian species closely related to E. revolutum, was completed in the laboratory, and the morphology of the larval stages and the adults obtained experimentally was studied. Planorbis planorbis and Anisus vortex were the first intermediate hosts in the brackish Lake Durankulak on the Bulgarian Black Sea coast. Characteristic features of the cercaria include: a prominent collar with 37 spines; a tail as long as the body and with seven conspicuous fin-folds, the two ventral fin-folds being very close to each other; and a specific number and distribution of both the para-oesophageal gland-cell outlets and sensilla. The adult is characterised by: a very elongate body with a constriction at the posterior border of the ventral sucker; a large head collar with relatively small spines; a spherical ventral sucker which is only about half the maximum body width; a long cirrus-sac reaching posteriorly dorsal to the middle of the ventral sucker; indented subglobular testes; and a vitellarium forming two lateral fields of follicles which are almost confluent in the post-testicular space. The species described in this study resembles E. miyagawai, as described by Kosupko, in the morphology of larval stages and both the site and the general morphology of the adults. It differs from both E. revolutum, as described by both Kanev and Nasincová, and E. echinatum (also referred to as E. lindoense and E. barbosai by Kanev). The re-examination of Kanev's voucher specimens from his experimental studies used in his delimitation of E. revolutum and E. echinatum showed that the specimens identified by him as E. revolutum represent two distinct forms which consistently differ both from each other and from the redescription of E. revolutum which was based upon them. It also revealed that a number of specimens were wrongly identified and erroneously treated as E. echinatum by Kanev and co-workers; these include members of different genera (Hypoderaeum and Echinoparyphium) and an Echinostoma species of the group possessing 47 collar spines. The relative merits of the features used by Kanev and co-workers in discriminating the closely related Echinostoma spp. are discussed in detail with respect to the experimental evidence provided by these authors.

Infrapopulations of trematode metacercariae were monitored in the snail Lymnaea stagnalis over 17 yr (1982-1999) at Chany Lake, Novosibirskaya Oblast', Russia. Eighteen trematode species were recorded. Patterns of occurrence varied from 4 species (Echinoparyphium aconiatum, Echinoparyphium recurvatum, Moliniella anceps, and Cotylurus cornutus) that persisted at relatively high prevalence (> 60% of samples) across sites, seasons, and years, to species that were very rare and sporadic in occurrence. The stability of the 4 common species was probably because of their occurrence either in a wide range of definitive hosts or in a host adapted to the extreme abiotic changes that occurred from year to year in these wetlands. The prevalence and mean abundance of C. cornutus were negatively correlated with water level in the wetlands; its prevalence was also correlated with water temperature. The mean abundance of M. anceps was positively correlated with water level. The most probable explanation for the cyclic dynamics of infections of the common species is change in population sizes and densities of definitive and intermediate hosts, which mediated cyclic alterations in water levels.

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Larval stages of an echinostome were found in Planorbis planorbis in a brackish water lake on the Black Sea coast of Bulgaria. The cercaria is a large-tailed form with 19 collar spines. The life-cycle was completed in the laboratory using aquarium-reared fishes (Lebistes reticulatus, Puntius tetrazona tetrazona, P. pentazona pentazona, P. nigrofasciatus, Carassius auratus auratus and Xiphophorus helleri) as second intermediate hosts and canaries as definitive hosts. The redia, cercaria, metacercaria and experimentally reared adults are described. The species is determined as Petasiger grandivesicularis Ishii, 1935, and its cercaria is compared in detail with those of related forms. A key to the known large-tailed echinostome cercariae from the Palaearctic Region is presented.