Invertebrate phylum whose name means "jawed mouth". The phylum is characterized by the presence of a pharynx with associated jaws and basal plate.

Gnathostomulids are small, fragile and elongate in structure, rarely exceeding 3mm in size, and usually between 0.5mm and 1mm. They have no circulatory system, a primitive gut, and usually no anus.
Their usual habitats are fine, anoxic marine sediments.