The preoral chamber in geophilomorph centipedes: comparative morphology, phylogeny, and the evolution of centipede feeding structures

Abstract

Geophilomorpha differ from other Chilopoda with respect to feeding mechanisms, having an inferred prevalence of food intake by pharyngeal sucking, and all components of the preoral chamber, mandibles, and head endoskeleton are so modified that inferring homologies with other chilopods is a challenge. Light and scanning electron microscopic documentation of the epipharynx, hypopharynx, mandibles, tentorium, and pharynx in 26 species sampling ten families of Geophilomorpha adds 24 phylogenetically informative new characters to a published morphological dataset for phylogenetic analysis. The mandibular gnathal edge of Geophilomorpha is recognized as being composed of pectinate lamellae only, i.e. lacking a molar plate and true teeth; the sclerotized lamellae traditionally identified as dentate are a modified pectinate lamella. An inferred transformation of the gnathal edge within Adesmata involves a reduction in the number of pectinate lamellae and their re-arrangement from imbricate to continuously aligned along the edge. Geophilid mandibles maintain a single pectinate lamella, to which the armature of the former ventral margin of the gnathal lobe is added distally to envelop the hypopharynx. This distal prolongation of the gnathal edge and transformation of the hypopharnyx into a tapering cone contribute new support for the monophyly of Geophilidae under implied character weighting. The interpretation that geophilomorphs have an immobile tentorium is consistent with the anatomy of Adesmata, but tentorial muscles in Placodesmata suggest mobility. Sensilla arrangements on the epi- and hypopharynx provide new characters for a grouping of Oryidae, Himantariidae, Schendylidae, and Ballophilidae, although cladistic analysis with other morphological characters also places Gonibregmatidae within this clade. © 2012 The Linnean Society of London, Zoological Journal of the Linnean Society, 2012, 165, 1–62.