Seriata

The Seriata are an order of turbellarian flatworms.
They are found in both freshwater and marine environments, and also include a number of species found in damp terrestrial conditions. Most are free-living, but the group includes the genus "Bdelloura", which lives comensally on the gills of horseshoe crabs. Seriatans are distinguished from other related groups by the presence of a folded pharynx and of a number of diverticula arising from the intestine. The intestine itself may be either simple or branched.