The adult head morphology of Dascillus (L.) (Dascilloidea: Dascillidae) and Glaresis Erichson (Scarabaeoidea: Glaresidae) and its phylogenetic implications

Abstract

External and internal structures of the adult head of Glaresis sp. and Dascillus cervinus are described in detail and compared with conditions found in other polyphagan representatives such as Rhipicera sp. and members of Staphyliniformia and Elateroidea. The structures examined do not support a clade Scarabaeoidea + Dascilloidea. No potential synapomorphic features of the head could be identifi ed. In Dascillus a very unusual confi guration of mouthparts is described for the fi rst time, notably the inframandibular antepipharynx. This complex apomorphic feature was also found in members of different groups of Elateroidea s.l., but not in other potentially related lineages. This suggests a possible monophylum ‘Elateroidea s.l. incl. Dascilloidea’. Additional new arguments for such clade are: characteristic scale-like setae on the galea and ligula; a ventrally expanded and bipartite foramen occipitale; a sclerotized tub-shaped prepharyngeal suspensorium; an epipharyngeal surface uniformly covered with microtrichia; similarly shaped mandibles with a concave ventral surface. Characteristics of Dascillus are the presence of a M. verticopharyngalis (plesiomorphic), the presence of two muscles of the posterior hypopharyngeal suspensorium, and bifurcate galeomeres II and ligular lobes. New arguments for a clade ‘Staphyliniformia incl. Scarabaeoidea’ are presented. The most important are the following: presence of a ‘craniobasimaxillary’ muscle; articulation of antennal club segments strongly excentric on outer margin of segments; distal club segment with characteristic sensory pouch; scapus with long bristle- or peg-like setae; ligula separated into a pair of oval shaped and anteriorly setiferous sclerites. Possible autapomorphies of Scarabaeoidea are the following: anterior part of clypeus projecting and covering the labrum; anterior clypeal margin concave and with a transverse row of trichia on its frontal or ventral surface; gula large, rectangular and strongly bulged; inner mandibular edge deeply interrupted by semimembranous lobe. Additionally, a revised terminology of head musculature is newly introduced for Coleoptera.