A Schmidtea nova (Benazzi, 1982)-like Population in SW Romania (Platyhelminthes, Tricladida, Dugesiidae), a Morphological Characterization.

This study has begun as exploratory research on freshwater planarians from southwestern Romania for faunal purposes. Specimens were sampled and processed for standard histology (paraffin wax embedding, horizontal and sagittal serial sections, and Haematoxylin-Eosin staining). The histological analysis provided evidence for a population belonging to the genus Schmidtea. The morphological and histological characteristics were compared with those of all other Schmidtea species. The histological slides reveal numerous diagnostic characters for Schmidtea nova: the presence of two nipples on the course of the ejaculatory duct; a partly sclerotized ejaculatory duct with a wide lumen; the knee-shaped bending of the distal part of the penis papilla in most specimens; the presence of the parovarium; and the egg-shaped distension of the bursal canal musculature. Unlike typical Schmidtea nova, this population shows a slightly different organization of the atrial space by the presence of a muscular atrial cavity named the atrial tube here. The newly discovered population shows affinities with other Schmidtea species: the presence of cephalic sensory fossae, similar to Schmidtea polychroa, and a potential asexual reproduction mechanism by fission, similar to Schmidtea mediterranea. The functional significance of the atrial tube and the taxonomic status of this population are hypothesized.