A preliminary study on the phylogenetic relationships of Copelatus Erichson (Coleoptera: Dytiscidae: Copelatinae) based on larval chaetotaxy and morphology

The phylogenetic relationships of the diving-beetle (Dytiscidae) subfamily Copelatinae are not well known. Some authors postulated a sister-group relationship between Copelatus Erichson and the remaining Dytiscidae, relying mainly on the absence of a mandibular channel in Copelatus. Other authors suggested a more derived position of the genus. Larval characters have been underutilized in phylogenetic studies, mainly because the larvae of many taxa within the family and, in particular, within Copelatinae are unknown. A comprehensive approach aimed to study the phylogenetic placement of a member of this subfamily based on larval characters has not been produced so far. In this study, the phylogenetic relationships of Copelatus are explored based on a cladistic analysis of 24 taxa and 120 chaetotaxic and morphological characters from larvae. For this purpose, larvae of Copelatus longicornis Sharp are described and illustrated in detail for the first time, with particular emphasis on morphometry and chaetotaxy, with the latter being unexplored until now. The results support a derived position of Copelatus within Dytiscidae, with a sister-group relationship between this genus and a clade formed by the subfamilies Lancetinae, Coptotominae, Laccophilinae, Colymbetinae, Matinae, and Dytiscinae, and part of Agabinae. No evidence was found for a sister-group relationship between Copelatus and the remaining Dytiscidae so that the absence of a mandibular channel in this genus is likely a reduction. Copelatus is supported by three apomorphies within Dytiscidae: mandibular channel absent, internal margin of the stipes with three robust spinulae, and seta MX8 inserted subapically on the galea.