1. ARTHROTARDIGRADA Marcus, 1927

Median cephalic cirrus usually present, rarely absent. Digitate legs with or without claws or non-digitate legs with claws always implanted directly into the legs.

Selected literature for further information: An early treatment of the arthrotardigrades can be found in Renaud- Mornant (1982a). Early general keys to marine arthrotardigrades can be found in Pollock (1976) for the northeastern USA, Ramazzotti & Maucci (1983) for all known species at the time of publication, and Morgan & O’Reilly (1988) for Scottish species.