Morphological evidence for the evolutionary origin of Astigmata (Acari : Acariformes)

A century ago, Antonio Berlese first discussed the close phylogenetic relat ionship between the large mite groups Oribatida and Astigmata. Since then, information having phylogenetic value has greatly increased and the paradig ms within which we interpret it have changed. Herein I refine the general h ypothesis that Astigmata originated within oribatid mites and suggest Malac onothridae as a possible sister group. Among the 14 apomorphies used to sup port the origin of Astigmata within oribatid mites are possession of latera l opisthosomal glands, regression of hysterosomal setal pair f(1), paired p relarval denticles, partially internalized chelicerae with incomplete adaxi al walls, an atelobasic rutellum, pretarsal condylophores that articulate p osteriorly with the tarsus, a dorsally fused palp tibia and tarsus and tran sdehiscent ecdysis. A further 13 apomorphies support the origin of Astigmat a at some level within Malaconothroidea. These include absence of an obliqu e labiogenal articulation, presence of a distal rutellar lamella, shortenin g of the palp tarsus, larval regression of hysterosomal seta f(2), loss of the bothridial sera in all instars, and several losses and modifications of leg setae. The hypothesis brings to light evolutionary questions that were previously obscured by incorrect or inappropriate classifications. The nom enclatural problems that arise from it are best solved by considering Astig mata as a subgroup within Oribatida. Exp Appl Acarol 22: 559-594 1998 Kluwe r Academic Publishers.