Morphology of the minute larva of Ptinella tenella, with special reference to effects of miniaturisation and the systematic position of Ptiliidae (Coleoptera: Staphylinoidea)

Abstract

External and internal features of minute reared ex ovo larvae of Ptinella tenella Erichson with the head widths ranging from 108 to 138mum are described. In total 139 setae (trichoid sensilla), 18 pores (non-trichoid sensilla), and 60 muscles were identified. The complexity of the chaetotaxy, the musculature of the head, the tentorium, and the digestive tract are not affected by the extremely small size of the larvae. Specific features, which may have resulted from miniaturisation are the elongate shape of the brain reaching the mesothorax posteriorly, the reduced condition of the thoracic sclerites and endosternites, the simplified musculature of the thorax and abdomen, and the loss of the abdominal spiracles. The monophyly of Ptiliidae is supported by the absence of head sutures, the presence of a setiferous protuberance close to the mandibular base, and the absence of a lacinia. Absence of abdominal spiracles and complete absence of eyes suggest the monophyly of a ptiliid subgroup which does not comprise Nossidium. Presence of a fimbriate galea is shared by larvae of Agyrtidae, Leiodidae, Ptiliidae, and Hydraenidae. The presence of a complex apical appendage on the distal maxillary palpomere and of hooks on abdominal segment X are possible synapomorphies of Ptiliidae and Hydraenidae. A description of the rearing procedure is provided and comments on feeding habits are made.