Descriptions of the preimaginal stages of Lancetes marginatus (Steinheil) and L. biremis Ríha (Coleoptera: Dytiscidae), and comparative notes with other Lancetes larvae

Abstract

All the preimaginal stages of Lancetes marginatus (Steinheil) and third instar larva of L. biremis Ríha are described and figured for the first time. Detailed analyses of the morphometry, chaetotaxy and porotaxy are provided, and comparisons with the immatures of other species of the genus are included. The larvae described have multifragmented urogomphi, the only larval synapomorphy that defines the genus Lancetes Sharp. Third instars also present a secondary subdivision in some of the cephalic appendages, which is a synapomorphy of Lancetes plus Dytiscinae. First instar larva of L. marginatus is distinguished from the remaining known first instars of Lancetes by the absence of primary pores FRe and MXa, and the presence of one additional minute seta on dorsal surface of antennomere 4 and one additional pore on urogomphus. Third instar of L. marginatus is unique by the absence of secondary dorsal setae on femur. Pupa of L. marginatus differs from that of L. angusticollis by the presence of fewer setae on the head, pronotum and abdominal terga V to VIII.