Protostome suborders

Echinostomata is a suborder of the parasitic flatworm order Plagiorchiida. The suborder contains numerous species that are parasitic in humans.

Maricola is a suborder of triclad flatworms including species that mainly inhabit salt water environments. However, some species are also known from freshwater or brackish waters.

The Hirudiniformes are one of the currently-accepted suborders of the proboscisless leeches (Arhynchobdellida). Their best-known member is the European medical leech, Hirudo medicinalis, and indeed most of the blood-sucking "worms" as which leeches are generally perceived belong to this group. In general, though some leeches suck blood, many are predators which hunt small invertebrates.

Articulina is an extant suborder of bryozoans in the order Cyclostomatida.

Tubificina is a suborder of haplotaxid annelid worms.