Morphology and chaetotaxy of larval Hypodessus cruciatus (Regimbart) (Coleoptera : Dytiscidae : Hydroporinae), and analysis of the phylogenetic relationships of the Bidessini based on larval characters

摘要

The phylogenetic relationships of members of the hydroporine tribe Bidessini are investigated based on a cladistic analysis of 30 taxa and 43 characters from larval morphology. For this purpose, the three larval instars of Hypodessus cruciatus (Regimbart) are described and illustrated for the first time, with particular emphasis on the morphometry and chaetotaxy. The consensus cladogram supports a monophyletic origin of the Bidessini based on the absence of the primary pore ABc, a unique feature within Hydroporinae. Amarodytes Regimbart is sister to the other Bidessini genera studied, being characterized by the presence of secondary setae on the first urogomphomere and the presence of an occipital suture in first-instar larva. Liodessus Guignot and Anodocheilus Babington are a monophyletic group and share the absence of a ventroapical spinula on the third antennomere. Hypodessus, Glareadessus Wewalka Bistrom and the clade Liodessus + Anodocheilus form a polytomy. Bidessini is resolved as derived within Hydroporinae, as part of a clade along with Hygrotini, Vatellini, Hyphydrini and Hydroporini (excluding Laccornellus Roughley Wolfe). Members of this clade share the absence of a galea and of setae MX8 and MX9. Within this grouping, Bidessini shares a common origin with Vatellini, Hyphydrini and part of Hydroporini, all these taxa being characterized by a cardo fused to the stipes.