A molecular framework for the phylogeny of the Pseudocerotidae (Platyhelminthes, Polycladida)

Systematic relationships within the cotylean family Pseudocerotidae were ex amined using nucleotide sequences of the D3 expansion segment of the 28S rD NA gene. A previously suggested separation of Pseudoceros and Pseudobiceros based on the number of male reproductive systems was confirmed. Regardless of the algorithm employed, Pseudoceros always formed a monophyletic clade. Pseudobiceros appeared to be paraphyletic; however, a constrained maximum parsimony tree was not significantly longer (2 steps, alpha = 0.05). Additi onally, the genera Maiazoon, Phrikoceros and Tytthosoceros were validated a s taxonomic entities, and their relationships to other genera within the fa mily were determined. Molecular data also supported species separations bas ed on colour patterns. An intraspecific genetic distance of 1.14% was found for Pseudoceros bifurcus, whereas the intrageneric distance was 3.58%. Gen etic distances among genera varied, with the closest distance being 2.048% between Pseudobiceros and Maiazoon, and the largest distance (8.345%) betwe en Pseudoceros and Tytthosoceros.