Larval morphology and phylogenetic position of Micromalthus debilis LeConte (Coleoptera: Micromalthidae)

External and internal structures of the cerambycoid and triungulin larvae of Micromalthus debilis are described and compared to features found in larvae of other groups of Coleoptera. The morphological data are evaluated with respect to the systematic position of Micromalthidae. A cladistic analysis was carried out with fifty characters. Micromalthidae are not closely related to Lymexylidae (Polyphaga: Cucujiformia) but belong to Archostemata, which is confirmed as a monophyletic unit. Micromalthidae are specialized in terms of morphology and life cycle and are characterized by a considerable number of larval autapomorphies. Their sister-group relationship with Cupedidae is supported by several apomorphic features, which are probably correlated with xylobiontic habits: head transverse and strongly rounded laterally, absence of stemmata, shortened antennae, presence of sternal asperities and presence of eversible lobes of segment IX. Cupedidae is monophyletic and Priamca is the sister group of the remaining genera of Cupedidae included in the analysis. A closer relationship between Tenomerga and Rhipsideigma is supported by several larval synapomorphies. The ancestral life style of larvae of Archostemata was probably xylobiontic. This is suggested by derived groundplan features of the suborder, which are also found in larvae of non-related, wood-associated families.