[2] Gastrotricha are microscopic animals ranging from 0.06-3.0 mm in body length.

Gastrotricha are aquatic free-living worms, belonging to the benthic meiofauna.

They have a high density in marine sediments and are often among top three of meiofauna found here, only surpassed by nematoda and harpacticoid Copepoda.

[2] Distribution of Paradasys subterraneus: British Isles, East North Atlantic, European waters (ERMS scope), Mediterranean Sea, Polish Exclusive Economic Zone, United Kingdom Economic Zone, Wimereux [3] The phylogenetic relationships of the Gastrotricha are still unclear: Morphological studies place Gastrostricha near the Gnathostomulida, the Rotifera, or the Nematoda.

Molecular data have shown that the Gastrotricha are sister taxon to the Platyhelminthes.