Gnathostomulida
The mouth is just behind the head, on the underside of the body. It has a pair of muscular jaws supplied with minute teeth, and a plate on the lower surface that bears a comb-like structure which they use to scrape smaller organisms off of the grains of sand that make up their anoxic seabed mud habitat. The mouth opens into a blind-ending tube in which digestion takes places; there is no anus.