Argia bicellulata Calvert, 1909

Vilela, Diogo Silva, Guillermo-Ferreira, Rhainer, Del-Claro, Kleber & Cordero-Rivera, Adolfo, 2018, Females of two species of Argia from Chapada dos Guimarães National Park, Brazil (Odonata: Coenagrionidae), Zootaxa 4420 (3), pp. 430-438: 431

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Argia bicellulata Calvert, 1909


Remarks on the female of Argia bicellulata Calvert, 1909 

Figs. 1–11View FIGURE 1View FIGURES 2‒3View FIGURES 4‒11.

Material examined. 3 ♀ (LESTES, Cod. ACR 0 3297, ACR 3322, ACR 3323), BRAZIL, Mato Grosso, Chapada dos Guimarães National Park, Rio Paciencia (15.3438° S, 55.8322° W, 280 m), 25 x 2015, R. Guillermo-Ferreira leg. [RGF].

Measurements. Fw 14.3, Hw 13.8, abdomen 18.8, total length 23.4.

Variations on the specimens examined (n = 3). The mesostigmal plates illustrated here ( Figs. 2‒3View FIGURES 2‒3) are from Calvert's single female. No variation on mesostigmal plate morphology was detected, comparing our specimens to figures of Calvert's female ( Figs. 2‒3View FIGURES 2‒3); Wing venation: no variation RP2 branching and postquadrangular cells; postnodal varied as follows: 10–11in Fw and 9–11 in Hw ( Table 1); size varied as follows: abdomen 18.3–20.2 (19.1±0.9), total length 23.3–25.9 (24.2±1.4), Fw 14.3–14.9 (14.5±0.3), Hw 13.8–14.6 (14±0.4). Body coloration had little variation on the specimens examined ( Figs. 4–11View FIGURES 4‒11), being more visible on the slightly different post ocular spots coloration ( Figs. 10–11View FIGURES 4‒11).

Differential diagnosis. Argia bicellulata  is the smallest known species of this genus (Garrison & von Ellenrieder 2015). Females are similar to males ( Figs. 1a ‒bView FIGURE 1) in having the black ventral thoracic coloration, a unique trait distinguishing A. bicellulata  from its sympatric congeners ( Figs. 8‒9View FIGURES 4‒11). The narrow posterodistally pointed digit-like mesostigmal lobe ( Figs. 2‒3View FIGURES 2‒3) differs from other sympatric species including the broadly arcuate lobe in A. botacudo Calvert, 1909  ( Figs. 12‒13View FIGURES 12‒13) and broad thumb-like lobe in A. tupi  ( Figs. 15‒16View FIGURES 15‒16). As stated by Calvert (1909), A. bicellulata  females have a coloration that resembles the male and by examining the females with living colors ( Figs. 4‒11View FIGURES 4‒11), we noticed some differences from its original description. The dorsal spot on the S2, blue in Calvert’s female, is pale on the examined females of this study. On the contrary, the S9 dorsal spot was pale in Calvert’s female, and our females have it in blue. The postocular spots are smaller than in males, and its coloration is violet, instead of the blue that is found in males. A remarkable trait is the number of Fw postquadrangular cells ( Table 1), numbered three in all our specimens (a frequent occurrence to Argia  species), which enforces the synonymy of Diargia Calvert, 1909  with Argia  , where Diargia  does not present strong enough characteristics to be considered a different genus ( Gloyd 1968). All other morphological traits on our specimens agree with Calvert’s description, such as the lack of vulvar spines on S9, hyaline wings with a reddish venation at the base, darkening distally.

Habitats and ecology. Both sexes were collected in palm swamp (i.e. veredas, Vilela et al. 2016) areas, in the same locality from where a new Argia  species was recently discovered (Vilela et al. 2018). At Paciência River the palm swamp had dense vegetation and was connected to the stream although we found A. bicellulata  only within palm swamp including small slow streams within the palm swamps. This species can be confused with Ischnura Charpentier, 1840  or Argentagrion Fraser, 1948  species due to its small size and flight behavior, flying through the dense grass vegetation of the swamp.