Larval morphology of Agnoshydrus Biström, Nilsson & Wewalka, 1997 (Coleoptera: Adephaga, Dytiscidae): description of A. thailandicus Okada, 2024 and phylogenetic comparison with other known Hyphydrini

Abstract

The three larval instars of the Thailand endemic Agnoshydrus thailandicus Okada, 2024 are described for the first time, including a detailed chaetotaxy analysis of the cephalic capsule, head appendages, legs, last abdominal segment, and urogomphi. The phylogenetic position of Agnoshydrus Biström, Nilsson & Wewalka, 1997 is studied based on a cladistic analysis of 12 Hyphydrini species (nine genera) and 59 morphological larval characters. Although the phylogenetic relationships of Agnoshydrus within the tribe Hyphydrini remain unresolved, it seems reasonable to suggest a closer relationship with Desmopachria Babington, 1842, Hovahydrus Biström, 1982, and Microdytes J. Balfour-Browne, 1946.