Procotyla fluviatilis Leidy, 1857

The mature specimens of Procotyla fluviatilis measure 12-20 mm in length and 2-5 in width. The head has a truncated shape but it varies while the animal is moving. It presents a subterminal adhesive organ that can be easily seen in the living individuals. It bulges out during the locomotion and it is flanked by two auricular projections of rounded shape that narrow at their posterior part in a sort of "neck".