Characteristics of Monogononta
Males present, but always smaller than females and often dwarfy and with reduced gut. Most species exhibit heterogony life-cycle. Body mostly unsegmented, at the best the foot may exhibit 2-4 ring-like segments. Very diverse morphologies of the rotary organ. Unpairy ovary. Mainly aquatic habitates, also marine. Free swimming, semi-sessile or sessile. Systematics are still under discussion. 2 or 3 orders. The 2-order system is as follows: 1. Pseudotrocha includes the Ploima. The preoral ring of cilia is derived from an anterior part of the mouth region (pseudotrochus). 2. Gnesiotrocha includes Flosculariacea and Collothecacea. The preoral ring of cilia stems from the the anterior rim of the circoapical band (real trochus).