Bifurcitus Brinck, 1945

Miller, Kelly B., Michat, Mariano C. & Ferreira Jr, Nelson, 2024, Reclassification of Cybistrinae Sharp, 1880 in the Neotropical Region (Coleoptera, Adephaga, Dytiscidae), with description of new taxa, ZooKeys 1188, pp. 125-168 : 125

Bifurcitus Brinck, 1945 stat. nov.

Figs 1 , 2 , 64 , 67

Bifurcitus Brinck, 1945: 8.

Type species.

Cybister giganteus Laporte, 1835: 99 by original designation (= Dytiscus lherminieri Guérin-Méneville, 1829).

Diagnosis.

Within Cybistrinae Bifurcitus have (1) the lateral margins of the pronotum and elytra margined with yellow, (2) males and females each with two equal-length metatarsal claws, and (3) the posterior metatibial spur bifid (Figs 1 , 2 ). These are the largest of all diving beetles with adult specimens 36-47 mm in total length ( Hendrich et al. 2019). Third instar larvae have (1) the median lobe of the frontoclypeus truncate apically with a tuft of setae (Fig. 67 ), (2) the median and lateral lobes of the frontoclypeus separated by a wide emargination (Fig. 67 ), (3) the lateral lobes of the frontoclypeus apically simple (Fig. 67 ), (4) the lateral lobes of the frontoclypeus obtusely angulate (Fig. 67 ), and (5) the cephalic capsule relatively short (head length / head width <1.20).

Phylogenetic relationships.

Bifurcitus is sister group to the similar Trifurcitus (Figs 75 , 76 ; Miller et al. 2007). Both have males and females with equal-length metatarsal claws and the anterior metatibial spur either bifid or trifid (although these two conditions may not be homologous) (Figs 1-3 ).

Discussion.

Although previous evidence suggested that the several subgenera of " Megadytes " are monophyletic, monophyly of this group is not supported here based in part on the discovery of undescribed cybistrine species with unique combinations of character states (Figs 75 , 76 ). Given the situation, it seems appropriate to recognize these subgenera at the genus rank including Bifurcitus .

There are three currently valid species in Bifurcitus which were differentiated and characterized recently by Hendrich et al. (2019).

Figures

Figure 75. One of seven cladograms derived from parsimony analysis of 57 morphological characters from Cybistrinae and other Dytiscidae (len = 105, CI = 68, RI = 92) with characters mapped using ' fast' optimization in WinClada. Black hash marks indicate unambiguous changes, white hash marks indicate homoplasious changes or reversals. Numbers above hash marks are character numbers, those below hash marks are derived state numbers.

Figure 76. Consensus cladogram of seven equally parsimonious cladograms from parsimony analysis of 57 morphological characters from Cybistrinae and other Dytiscidae morphology.

Figures 1 - 8. Cybistrinae morphological features 1 Bifurcitus lherminieri, right metatibia, posterior surface 2 Bifurcitus lherminieri, left metaleg, anterior surface 3 Trifurcitus robustus, left metaleg, anterior surface 4 Metaxydytes fraternus, left mesotarsomeres III-V, posterior surfaces 5 Cybister tripunctatus, left mesotarsomeres III-V, posterior surfaces 6 Megadytes latus, left half of metaventrite and left metacoxa (WV = metaventrite wing width, WC = metacoxal width) 7 Cybister tripunctatus, right metathoracic wing 8 Trifurcitus robustus, right metatrochanter, ventral surface. Scale bars: 1.0 mm.

Figures 62 - 66. Neotropical Cybistrinae species, female genitalia including left gonocoxosternite, ventral aspect 62 Metaxydytes fraternus 63 Paramegadytes glaucus 64 Bifurcitus lherminieri 65 Trifurcitus robustus 66 Cybister fimbriolatus. Scale bars: 1.0 mm.

Figures 67 - 71. Third instar larva, anterior clypeal margin 67 Bifurcitus magnus 68 Megadytes latus 69 Metaxydytes carcharias 70 Paramegadytes glaucus 71 Trifurcitus fallax.