Species diversity among the genus Monorchis (Digenea: Monorchiidae) parasitic in marine teleosts: molecular, morphological and morphometrical studies with a description of Monorchis blennii n. sp.

Molecular, morphological and morphometrical studies were conducted on two species of the genus Monorchis (Monorchiidae), Monorchis parvus and Monorchis monorchis, collected in different fish hosts from the Mediterranean Sea. The analysis of internal transcribed spacer 1 sequences of ribosomal DNA showed that M. monorchis specimens from Parablennius gattorugine were strongly divergent (12.9%) from specimens of this species collected in Spondyliosoma cantharus and Diplodus puntazzo. This high genetic variation was confirmed by the analysis of morphological structures and morphometrics, which showed that M. monorchis specimens from P. gattorugine can be distinguished from those of S. cantharus and D. puntazzo by several morphological characteristics, including body size, number and distribution of vitelline follicles, testis shape, structure of the cirrus pouch, and number of eggs. Our results show that M. monorchis specimens isolated from P. gattorugine represent a clearly distinct entity from M. monorchis found in the other hosts, which has enabled us to describe a new species, Monorchis blennii n. sp.