Laccornellus (Coleoptera: Dytiscidae), a new hydroporine genus from austral South America

Abstract

Laccornellus, new genus, is proposed for two austral South American species previously assigned to Laccornis Gozis (L. lugubris (Aube, 1838), the type species, known from Argentina and Uruguay, and L. copelatoides (Sharp, 1882), known from Chile). The valvifer is absent in the adult stage of females of these species and the males have a greatly enlarged internal sac on the aedeagus; these characters exclude them from Laccornis. The most similar and possibly most closely related genus to Laccornellus is the African genus Canthyporus Zimmermann, although no conclusive synapotypy was found. Relationships of extant, plesiotypic hydroporines remain problematic; however, divergence of Laccornellus and Canthyporus probably began about 120 million years ago when Africa and South America separated. The vicariant event preceding divergence of L. copelatoides and L. lugubris probably was the uplift of the Andes Mountains which began in the late Oligocene – early Miocene.

A Phylogenetic Investigation of Hydrovatus, Methlini and Other Plesiotypic Hydroporines (Coleoptera: Dytiscidae)

“…However, further study (Roughley and Wolfe, 1987) adequately demonstrated that those species formed a distinct unit and they were assigned to a new genus, Laccornelius, and Laccornellus is included in the analysis below.…”

Taxonomic revision of the Ethiopian genus Canthyporus (Coleoptera Dytiscidae)

“…Roughley & Wolfe (1987) discussed in their introduction of Laccornellus also Canthyporus, Laccornis, and the tribes Methlini and Hydrovatini and their intergeneric relationships. They identified a number of characters in common but did not consider any of them as a good synapomorphy for monophyly.…”

Description of the Second and Third Instars ofLaccornellus lugubris(Aubé) (Coleoptera: Dytiscidae: Hydroporinae)

“…Laccornellus lugubris is a rare species collected only sporadically and always in low numbers of specimens. Previous to this study, it was known from Uruguay, central-eastern Argentina (Buenos Aires and Entre Ríos Provinces), and southern Brazil (Roughley and Wolfe 1987;Trémouilles 1995;Benetti and Régil Cueto 2003). The finding of both adults and larvae in Patagonia (Chubut Province) considerably expands the southern distributional limit of the species.…”

“…The genus is presently included in the tribe Hydroporini (Nilsson 2001), though several independent studies based on adult (Roughley and Wolfe 1987;Wolfe 1988;Miller et al 2006) and larval ) morphology strongly suggested a position of Laccornellus outside the Hydroporini, more closely related to members of other, more ancestral tribes such as Methlini, Laccornini, and possibly Hydrovatini. The genera Laccornellus and Canthyporus Zimmermann are postulated to be very closely related phylogenetically (Roughley and Wolfe 1987;Nilsson 1991).…”

“…Laccornellus lugubris is a rare species known so far from Uruguay, central-eastern Argentina, and southern Brazil (Roughley and Wolfe 1987;Trémouilles 1995;Benetti and Régil Cueto 2003). The fact that Laccornellus is the only genus of the Hydroporini present in South America, summed to its presumably plesiomorphic condition, place it as a very interesting group of beetles both from a biogeographic and a phylogenetic point of view.…”