Hydrodessus bimaculatus, Miller, Kelly B., 2016

Miller, Kelly B., 2016, Revision of the Neotropical diving beetle genus Hydrodessus J. Balfour-Browne, 1953 (Coleoptera, Dytiscidae, Hydroporinae, Bidessini), ZooKeys 580, pp. 45-124 : 63-64

Taxon classification Animalia Coleoptera Dytiscidae

Hydrodessus bimaculatus sp. n. Figs 10, 44

Type locality.

Venezuela, Territoria Federal Amazonas, Cerro de la Neblina, basecamp, 0.833°N, 66.167°W.

Diagnosis.

This species is moderately elongate and dorsally and ventrally nearly concolorous red, except with small pale, subtriangular maculae subapically and the apex of the elytron is narrowly pale (Fig. 10A). The elytral apices are not dehiscent (Fig. 10A). The lateral elytral carinae extend about 1/4 length of the elytron (Fig. 10B). The prosternal process is very broad, broadly excavated medially, and slightly broader anteriorly (Fig. 10C). The metaventrite carinae are prominent, not medially constricted and posteriorly somewhat divergent, but the posterior apices are located distinctly mediad of the anterior apices of the metacoxal lines (Fig. 10C). The male median lobe in lateral aspect is relatively small basally with the apical portion slender, linear medially, abruptly curved subapically and with apex linear and narrowed to pointed apex (Fig. 10C). The median lobe in ventral aspect is bilaterally symmetrical and very broadly expanded medially (Fig. 10D). Apically the median lobe is abruptly broadly angulate (Fig. 10D). The lateral lobe is moderately broad, curved basally and apically broadly narrowed to narrowly rounded apex (Fig. 10F). This species is most similar to Hydrodessus disjunctus and Hydrodessus biguttatus . From Hydrodessus biguttatus it differs in the absence of dehiscent elytral apices and the shape of the male genitalia. From Hydrodessus disjunctus this species differs in size ( Hydrodessus bimaculatus are longer, TL> 3.5 mm) and the male genitalia are different.

Description.

Measurements. TL = 3.8-3.9 mm, GW = 1.5-1.7 mm, PW = 1.4-1.5 mm, HW = 1.1 mm, EW = 0.6 mm, TL/GW = 2.2-2.3, HW/EW = 1.7. Body elongate, apically pointed, lateral margins strongly discontinuous between pronotum and elytron (Fig. 10A).

Coloration (Fig. 10A). Head and pronotum red. Elytra red, with diffuse, yellow macula subapically and with apex yellow. Antennae and palpi yellow-red. Legs yellow. Venter red-brown, lighter on epipleuron and apex of abdomen.

Sculpture and structure. Head broad; anterior clypeal margin broadly rounded; surface with fine microreticulation and with sparse, indistinct punctures; eyes large. Pronotum cordate, widest anterior to middle; lateral bead fine, continuous along margin; surface with fine microreticulation and punctation variable with some larger and some smaller punctures. Elytra elongate, apically pointed; lateral carina distinctive, extending about 1/4 length of elytron (Fig. 10A); surface covered with fine punctation. Prosternum medially tectiform and setose; prosternal process subquadrate, broad, broadest at anterior laterally-expanded angles, medially strongly impressed, apex broadly truncate (Fig. 10C). Metaventrite with anterior process broad, slightly expanded anteriorly, apically truncate; metasternal carinae distinct, diverging posteriorly (Fig. 10C); surface with fine punctures. Legs with most surfaces covered with fine punctures; pro- and mesotibiae moderately broad; metatibia with posteroapical brush of setae; metatrochanter not strongly offset, apically pointed; metacoxae covered with fine punctures; metacoxal lines moderately distinct, straight and distinctly divergent anteriorly (Fig. 10C). Abdomen covered with fine punctures; ventrite VI rounded with small, spinous, medioapical lobe.

Male genitalia. Median lobe bilaterally symmetrical, in lateral aspect strongly curved basally and subapically, straight medially, basal portion small, apical portion robust, apically straight and evenly narrowed to pointed apex (Fig. 10D); in ventral aspect basally narrow, medially and apically very broad and robust, lateral margins broadly curved, apically abruptly convergent to broadly angulate apex (Fig. 10E). Lateral lobe broad basally, elongate, moderately narrow apically, ventral margin sublin ear, dorsal margin sinuate, margins convergent to narrowly rounded apex, apicodorsal margin with series of setae (Fig. 10F).

Female genitalia. Not examined.

Sexual dimorphism. Male pro- and mesotarsi I–III more broadly expanded than female and ventrally with several large adhesive setae.

Variation. Few specimens were examined and no significant variation was discovered.

Etymology.

This species is named bimaculatus, Latin for "two spots," for the two maculae present apically on the elytra.

Distribution.

This species is known only from Cerro de la Neblina, Amazonas, Venezuela (Fig. 44).

Habitat.

Hydrodessus bimaculatus has been collected from "rocks in rapids" and "netted along margins" of the Rio Baria..

Specimens.

Holotype: ♂ in MIZA labeled, "VENEZUELA,T.F.Amaz. Cerro de la Neblina Basecamp, 140 m. 0°50'N, 66°10'W 28 January 1985/ seined from rocks in rapids of Rio Baria P.J. & P.M.Spangler, R.Faitoute,W.Steiner/ HYDRODESSUS CRAFTI [handwritten]/ HOLOTYPE Hemibidessus bimaculatus Miller, 2016 [red label with black line border]."

Paratype, 1 total. Venezuela; Amazonas, Cerro de la Neblina, basecamp, 140m, 0°50'N, 66°10'W, 20 Feb 1985, netted along margins of Rio Baria, P.J. and P.M. Spangler, R. Faitoute, W. Steiner (1, USNM).