Gastrotricha
Clades: Platyzoa; Protostomia; Animals.
Genera: ± 700 species have been described.
The gastrotrichs (from Greek γαστερ, gaster "stomach" and θριξ, thrix "hair") are a phylum of microscopic (0.06-3.0 mm) animals abundant in fresh water and marine environments. Most fresh water species are part of the periphyton and benthos. Marine species are found mostly interstitially in between sediment particles.
Zoology
Gastrotricha are microscopic, bilaterally symmetric animals, with a complete gut, that live short, about three days. They demonstrate eutely,developing to a particular number of cells, and further growth coming only from an increase in cell size. The body is covered with cilia, especially about the mouth and on the ventral surface, and has two terminal projections with cement glands that serve in adhesion.
One gland secretes the glue and another secretes a de-adhesive to sever the connection. Their locomotion is primarily powered by hydrostatics. They reproduce entirely by parthenogenesis. They have an acoelomate, which was formerly seen as body cavity, pseudocoel.
Taxonomy
Their relationship to other phyla is unclear. Morphology suggests that they are close to the Gnathostomulida, the Rotifera, or the Nematoda. On the other hand genetic studies place them as close relatives of the Platyhelminthes, the Ecdysozoa or the Lophotrochozoa.