Morphometric discriminant analysis of three species of Petasiger Dietz, 1909 (Digenea: Echinostomatidae)

The morphology of three Palaearctic species of the genus Petasiger Dietz, 1909, parasitizing grebes and exhibiting a significant degree of overlap, was studied. Ninety-three specimens belonging to P. grandivesicularis, P. neocomense and P. pungens were compared using univariate and multivariate statistical analyses of 17 metrical characters. A stepwise discriminant analysis run in three variants and based on seven variables (body length, body width, oral sucker diameter, pharynx diameter, ventral sucker diameter. posterior testis diameter and oesophagus length) yielded a 100 % accurate classification. The first canonical discriminant function separated specimens belonging io P. grandivesicularis and P. pungens, and the second function effectively differentiated the P. neocomense sample. Two variables (pharynx diameter and oesophagus length) were strongly correlated with the canonical functions and, when used alone, discriminated the three Petasiger spp. A simple key based on two variables used in the discriminant analyses and a table of the qualitative and quantitative characters used for the identification of the three species are presented.