Ecdysozoa: Tardigrada

Pseudobiotus, a tardigrade or water bear Photo by Antonio Guillén Flickr: EOL Images , Encylclopaedia of Life, Creative Commons Attribution Non-Commercial Share Alike

Tardigrades, or "water bears", are tiny, eight-legged, segmented creatures, accorded subphylum (Cavalier-Smith (1998)) or phylum ( Neilsen 2001) rank. They live in water, although the 'water' may be the moisture held between the leaves of a moss, and they are capable of producing a thick-walled, protective resting cyst and surviving long periods of dessication (and, apparently, immersion in alcohol, freezing, boiling, vacuum and irradiation; Tudge 2000, p. 257). Closely related to onychophores and arthropods (Budd 2001), they would have evolved from a Cambrian abcestor not unlike Aysheaia. By the Middle Cambrian they had already acheived microscopic size and other specialised features of the group (Müller et al 2005) - Chris Clowes and MAK120425