Tomedontus Lugo-Ortiz & McCafferty, 1995

Falcão, J. N., Salles, F. F. & Hamada, N., 2010, The adults of Harpagobaetis Mol and Tomedontus Lugo-Ortiz and McCafferty (Ephemeroptera: Baetidae) with notes on the nymphal stage, Zootaxa 2530 (1), pp. 39-46 : 42

Tomedontus Lugo-Ortiz & McCafferty, 1995

( Figs. 6–9, 13–14, 18–20)

Tomedontus Lugo-Ortiz & McCafferty, 1995: 237 , Domínguez et al. 2006: 177.

Male imago. Turbinate eyes circular, length 1.2× width; stalk height equal to width of dorsal portion; inner margins widely separated from each other ( Figs. 6–8).

Thorax with anteronotal protuberance rounded ( Figs. 7–8). Forewing ( Fig. 9) with paired marginal intercalary veins; length of each intercalary vein about 0.6× distance between adjacent longitudinal veins; length of fore wing about 2.6× width; stigmatic cross veins not reaching Sc. Hind wing absent. Metascutellar protuberance posteriorly directed ( Fig. 8).

Genitalia ( Figs. 13, 14) with forceps three-segmented. Forceps segment I without projections, 0.6× length of segment II; distance between segments about 2.4× width of segment I. Forceps segment II with strong medial projection. Forceps segment III long, about 2× as long as wide; about 0.3× length of segment II. Posterior margin of subgenital plate straight.

Comments. Male adults of Tomedontus can be distinguished from the males of other Baetidae genera by the following combination of characters: dorsal portion of turbinate eye circular ( Fig. 6); forewing with paired marginal intercalary veins ( Fig. 9); hind wing absent; forceps three-segmented, segment II with strong medial projection ( Figs. 13, 14); 5), subgenital plate without projections.

In the key proposed by Domínguez et al. (2006) the genus Tomedontus will key out as Chane Nieto. However , the shape of the dorsal portion of the turbinate eyes can differentiate these genera: they are circular in Tomedontus and oval in Chane ( Figs. 18−20).

The nymph of Tomedontus ( Figs. 18−20) was adequately characterized by Lugo-Ortiz & McCafferty (1995) and later by Domínguez et al. (2006), except for two characteristics. Firstly, the shape of the frontal suture, which was not described by these authors, is sinuous or bell shaped in Tomedontus ( Fig. 18). Secondly, and more important, the gills are not present on abdominal segments 1−6 as pointed out in the original description, but on abdominal segments 2−7 ( Fig. 20) as in other South American genera such as Chane , Guajirolus Flowers , Americabaetis Kluge and Zelusia . The shape of forceps segment I and gill location suggest that Tomedontus may be more closely related to Chane and Guajirolus , despite the phylogeny recently proposed by Nieto (2010). However, a new cladistic analysis including these characters should be performed in order to corroborate this hypothesis.

Nymphs of Tomedontus were collected exclusively on sandy, shallow, small streams (igarapés) in the cities of Manaus (Reserva Adolfo Ducke, type-locality of the T. primus ) and Presidente Figueiredo, Amazonas, inhabiting leaves of hydrophytes in areas with moderate current. Given the habitat of the nymphs, and remarkable mouthparts morphology ( Figs. 18−19, also see Lugo-Ortiz & McCafferty 1995, Figs. 10−15), they possibly graze on epiphyton (periphyton attached to plants) as stated by Baptista et al. (2006) for other Baetidae with somewhat similar mouthpart morphology.