Gastrotricha

Gastrotricha is a phylum of tiny, free-living, freshwater and marine-dwelling animals. They are bilaterally symmetrical and acoelomate[?]. They have a mouth and an anus, as well as circulatory and nervous systems with some poorly understood sensors. The skeleton is hydrostatic[?]. The body surface has cilia, scales, and adhesive tubes. About 450 species are known, with no fossils.