Comparative karyological analysis of three members of Allocreadiidae (Digenea): taxonomic and phylogenetic implications.

Chromosome number and morphology were studied in three allocreadiid species from mitotic metaphases of intramolluscan stages using karyometric analysis. Bunodera luciopercae has a diploid number 2n=14, with two large pairs of metacentrics, one pair of submeta-subtelocentrics, and four pairs of acrocentrics. Karyotype of Allocreadium isoporum, 2n=14, with two large pairs of metacentrics and five pairs of acrocentrics was recognized to be closely related to that of B. lucioperca. The most conspicuous interspecific difference occurs in the centromere position of the chromosomes of the pair 3. The possible reasons of the discrepancies between data reported therein and the karyological information previously published on these two species are discussed. Crepidostomum sp. has 2n=12, with one pair of large metacentrics and five pairs of acrocentrics and is more distantly related karyologically to the other two members of the family. Evolutionary considerations based on comparison of the chromosomes of Allocreadiidae and other studied families of the suborder Xiphidiata suggest that allocreadiids are karyotypically distinct. The placement of Allocreadiidae and Opecoelidae in the superfamily Allocreadioidea is questioned.