The epistomo-labral plate and lateral lips in solifuges, pseudoscorpions and mites

Solifugae and Pseudoscorpiones are accepted by most recent authors as siste r taxa, forming a clade Haploenemata. The sister group of Haploenemata is l ess certain. Most recent authors have accepted Acari as monophyletic and pl aced them as sister group of Ricinulei, although a (Ricinulei +Trigonotarbi da) relationship has also been proposed. In an attempt to resolve some of t hese phylogenetic questions, the mouthparts of Solifugae, Pseudoscorpiones and Acari were investigated. In these three orders the mouth is covered dor sally by a projecting epistomo-labral plate (a fused epistome and labrum), and ventrolaterally by a pair of finger-like lateral lips, probably derived from the coxae of the pedipalps. This character complex of a epistomo-labr al plate + lateral lips is not seen in other arachnids, although similar, a nd perhaps homologous structures occur in Opiliones. The epistomo-labral pl ate + lateral lips are interpreted here as a possible synapomorphy for (Aca ri (Solifugac + Pseudoscorpiones)).