The larval cephalic morphology of the enigmatic boreid Caurinus dectes (Mecoptera) and its phylogenetic significance

Abstract

The species Caurinus dectes was described in 1979 by L. Russell and assigned to the mecopteran family Boreidae. A description of the immature stages published three years later provided important information. In the present study we re-examined larvae which became available through recent collecting efforts. External and internal features of the head are described and documented in detail. The systematic position of Caurinus and Boreidae is discussed. The orthognathous head is mainly characterized by plesiomorphic features such as the complete tentorium with well-developed dorsal arms and a broad bridge, the presence of seven well-developed stemmata, the free labrum, the simple mandibles with a basal molar area but without complex mesal appendages, the presence of a tentorio-mandibular muscle, the well-developed set of dorsal and ventral pharyngeal dilators, the placement of the brain and suboesophageal ganglion within the head, and the presence of an occipital furrow. Derived features are deformations of the brain related to size reduction and the greatly reduced labium. The phylogenetic interpretation remains ambiguous. The orthognathous head and some postcephalic features are potential synapomorphies of Boreidae and Pistillifera, whereas the presence of secondary compound eyes is a potential synapomorphy of Pistillifera and Nannochoristidae.