Bessierus Thomas &Orth

Domínguez, Eduardo, Cuezzo, María Gabriela & Clavier, Simón, 2019, The phylogenetic relationships of the two-winged South American Leptophlebiidae genera revisited with first description of the male imago of Bessierus Thomas & Orth (Insecta: Ephemeroptera), Zootaxa 4674 (3), pp. 375-385 : 377-379

publication ID

https://doi.org/10.11646/zootaxa.4674.3.6

publication LSID

lsid:zoobank.org:pub:77E25A64-82B1-4DDA-84F5-35A87766F1F7

persistent identifier

https://treatment.plazi.org/id/F21BE822-4F75-FFFA-FF12-F99FFCE7FCC7

treatment provided by

Plazi

scientific name

Bessierus Thomas &Orth
status

 

Genus Bessierus Thomas &Orth  

Thomas & Orth, in Thomas et al., 2000: 49 (nymph). (Type-species: Bessierus doloris Thomas & Orth   , original designation). Domínguez, Molineri, Pescador, Hubbard & Nieto, 2006: 356; Domínguez, 2009: 70; Nascimento, Barcelos-Silva & Salles, 2011: 191.

Diagnosis: The male imago of Bessierus   can be separated from all other genera of Leptophlebiidae   by the following combination of characters: (1) fork of vein MA of forewing asymmetrical ( Fig. 2A View FIGURE 2 ); (2) vein ICu1 attached to vein CuA by a cross vein, and vein ICu2 attached at base to vein ICu1 by a cross vein; (3) hind wings absent; (4) tarsal claws of a pair dissimilar, one apically hooked, the other blunt ( Fig. 2B View FIGURE 2 ); (5) forceps sockets fused ( Figs 2 View FIGURE 2 C-D); penes widely divided in apical 2/3, apex of each penis lobe with a laterally orientated broad projection ( Figs 2 View FIGURE 2 C-D); (7) forceps segment 1 smoothly roundly, broadened in basal 1/3 ( Fig.2C View FIGURE 2 ).

Description of the male imago (in alcohol). Length of body 2.9 – 3.0 mm, forewing length 3.0- 3.1 mm. Head ( Figs 3 View FIGURE 3 A-B): Eyes meet on meson of head ( Fig. 3A View FIGURE 3 ), lower portion of eyes approximately 4/5 length of upper portion ( Fig. 3B View FIGURE 3 ).

Wings ( Fig. 1A View FIGURE 1 ). Maximum width of forewing is 1/3 of maximum length of forewing; vein Rs of forewing forked 1/5 of distance from base to margin; vein MA forked a little more 1/2 of distance from base to margin, fork asymmetrical, distal portion of vein MA not sagged posteriorly; vein MP forked 3/8 of distance from base to margin, fork symmetrical, distal portion of vein not sagged posteriorly; vein ICu1 attached to vein CuA by a cross vein, and vein ICu2 attached at base to vein ICu1 by a cross vein. Hind wings absent.

Legs. Ratio of segments of male forelegs, 0.42:1.0 (0.96 mm): 0.06:0.23:0.19:0.08: 0.05. Claws on each leg dissimilar, with one apically hooked and one blunt, pad-like ( Fig. 2B View FIGURE 2 ). Male genitalia ( Figs 2 View FIGURE 2 C-D): segment II of forceps subequal in length to segment III, segment II of forceps 1/6 length of segment I; forceps segment I smoothly roundly broadened in basal 1/3 ( Fig. 2C View FIGURE 2 ); forceps sockets fused, forming a single cavity ( Fig. 2D View FIGURE 2 ); length of styliger plate along median line 1/3 maximum width, posterolateral corners slightly developed; penes widely divided in apical 2/3, apex of each penis lobe with a laterally orientated broad projection ( Figs 2 View FIGURE 2 C-D).

Comments. Among the diagnostic characteristics of Bessierus   (also shared with Perissophlebiodes   ), the fused forceps sockets are very unusual. Until recently this has been considered an exclusive characteristic of Thraulodes Ulmer. Mariano (2010)   also described this character for two species of Simothraulopsis Demoulin   from Brazil. More recently, Nascimento et al. (2011), in their revision of this genus, stated the fusion of the forceps socket as a diagnostic character. According to Domínguez (2009), Thraulodes   is not closely related neither to Bessierus   nor Perissophlebiodes   . Simothraulopsis   , on the other hand, together with Homothraulus Demoulin   , was the sister group of Perissophlebiode s and Bessierus   . In that analysis, the adult of Bessierus   and Perissophlebiodes   remained unknown, hence it was impossible to know the state of this character.