A quantitative approach to the evaluation of the morphological variabilityof two echinostomes, Echinostoma miyagawai Ishii, 1932 and E-revolutum (Frolich, 1802), from Europe

A comparative morphometric analysis was conducted on two European species o f Echinostoma in order to examine the degree of the variability in the metr ical characteristics of the adults and to assess their value in discriminat ing species. Adult E. miyagawai and E. revolutum, obtained experimentally, were compared using univariate and multivariate statistical analyses of 35 and 25 metrical characters, respectively. All subsets of worms of different ages represented homogeneous samples with respect to their morphometric ch aracteristics; however, univariate analyses revealed significant difference s in 22 and 23 variables between the corresponding age subsets of the two s pecies, and it was found that the different allometric growth patterns cont ribute to this. The variables, body width at the posterior border of the ve ntral sucker, pharynx length and width, ovary length, testes length and wid th and length of the pre-ovarian region, exhibited isometric or positive al lometric growth in E. miyagawai and negative allometry in E. revolutum. A c luster analysis based on 61 specimens and 25 variables separated E. revolut um and E. miyagawai unambiguously, producing an exact ordering of the speci mens with respect to their identity and age. A forward stepwise discriminan t analysis identified five variables (body width at the posterior border of ventral sucker, head collar width, length of oesophagus, width of ventral sucker and length of the pre-ovarian region) which yielded a 100% accurate classification of the two species. We suggest, therefore, that the morphome tric characteristics of the adult worms should be used in studies attemptin g the identification of species or isolates of Echinostoma spp. More compar ative data need to be gathered in order that the species boundaries within the 'revolutum' group be defined more accurately.