Hydrodessus biguttatus (Guignot, 1957)

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 : 59-63

Taxon classification Animalia Coleoptera Dytiscidae

Hydrodessus biguttatus (Guignot, 1957) Figs 6, 9, 49

Brinckius biguttatus Guignot, 1957: 39.

Hydrodessus biguttatus , Young 1969: 2; 1970: 157; Spangler 1985: 88; Biström 1988: 37; Nilsson 2001: 236.

Hydrodessus fragrans Spangler, 1985: 82; Young 1969: 2; Biström 1988: 37; Nilsson 2001: 236. syn. n.

Type locality.

Brinckius biguttatus Guignot: Brazil, Pará State, Cachimbo. Hydrodessus fragrans Spangler: Guyana, Mazaruni-Potaro District, Takutu Mountains, 6°15'N 59°5'W.

Diagnosis.

This species is elongate and dorsally and ventrally nearly concolorous red, though some specimens have indistinct pale, subtriangular maculae subapically and the apex of the elytron more pale (Fig. 9A). The elytral apices are slightly dehiscent (Fig. 9A). The lateral elytral carinae are somewhat variable from about 1/4-2/5 length of elytron (Fig. 9B). The prosternal process is very broad and broadly excavated medially with the lateral margins subparallel (Fig. 9C). The metaventrite carinae are promi nent, not medially constricted and posteriorly somewhat divergent, but the posterior apices are located distinctly mediad of the anterior apices of the metacoxal lines (Fig. 9C). The male median lobe in lateral aspect has the basal portion relatively small, the apical portion is elongate, slender and evenly and broadly curved (Fig. 9D). The apex is elongate and sharply pointed (Fig. 9D). The median lobe in ventral aspect has the margins nearly parallel to the convergent, narrowly rounded apex (Fig. 9E). The lateral lobe is broad, curved medially and apically broadly rounded (Fig. 9F). This species is most similar to Hydrodessus bimaculatus and Hydrodessus disjunctus . Those species do not have dehiscent elytral apices and the male genitalia are different (see under those species).

Description.

Measurements. TL = 3.9-4.6 mm, GW = 1.7-2.0 mm, PW = 1.4-1.7 mm, HW = 1.1-1.2 mm, EW = 0.7 mm, TL/GW = 2.3-2.4, HW/EW = 1.6-1.7. Body shape elongate, narrow, lateral outline strongly discontinuous, apically pointed with elytra dehiscent apically (Fig. 9A).

Coloration (Fig. 9A). Head and pronotum orange. Elytra red with small lateral pale macula, larger diffuse subtriangular subapical pale macula, and elytral apices yellow. Antennae, palps and legs orange. Venter orange on most surfaces, yellow-brown on mesocoxae and metasternum.

Sculpture and structure. Head broad, anterior clypeal margin broadly curved, slightly flattened dorsoventrally; surface covered with minute punctures; eyes large. Pronotum subcordate, widest slightly anterior to middle (Fig. 9A); lateral bead fine and continuous; surface shiny, covered with fine punctures. Elytra long, apices pointed and finely but distinctly dehiscent apically (Fig. 9A); lateral carina distinct, extending about 2/5 length of elytron (Fig. 9B); surface covered with fine punctures. Prosternum medially weakly tectiform and setose; prosternal process very broad, widest at anterior lobes, margins slightly convex, convergent to broadly truncate apex, broadly excavated medially (Fig. 9C). Metaventrite with anterior process prominent, apex trunctate, slightly expanded subapically, carinae distinctive anteriorly, moderately divergent becoming slightly less distinctive and broader posteriorly, converging with posterior margin well mediad of anterior apices of metacoxal lines (Fig. 9C); surface covered with fine punctation. Legs shiny, relatively impunctate; metatibia with distinctive brush of dense, elongate setae on postero-apical surface; pro- and mesotibiae moderately slender; metatrochanter distinctly offset, apically minutely bispinous (Fig. 6); metacoxa evenly covered with fine punctures; metacoxal lines broadly separated, broadly divergent anteriorly (Fig. 9C). Abdomen shiny, evenly covered with fine punctures; apex of VI broadly pointed.

Male genitalia. Median lobe bilaterally symmetrical, in lateral aspect broadly and evenly curved to narrow, narrowly rounded apex (Fig. 9D); in ventral aspect nearly parallel-sided throughout most of length, narrow, apically abruptly narrowed to narrowly rounded apex (Fig. 9E). Lateral lobe moderately broad basally, apically gradually narrowed, apex obliquely rounded with dense region of short setae (Fig. 9F).

Female genitalia. Not examined.

Sexual dimorphism. Male pro- and mesotarsi I–III slightly more broadly expanded than female and ventrally with several large adhesive setae. Some females specimens with fine dorsal microsculpturing which makes surface matte, other females and males dorsally shiny.

Variation. Specimens are conspicuously variable in size. There are relatively few specimens available to determine whether there is a geographic component to size variability, and other attributes (male genitalia, etc) do not evidently vary with size. There is some variation in the extent of elytral maculation. Given the variation, it is certainly possible that multiple species are involved, thought the diagnostic characters are consistent across the specimens examined.

Distribution.

This species has been collected from Para, Brazil north through Suriname and Guyana to southern Venezuela (Fig. 49).

Habitat.

Specimens have been collected from blacklights in tropical forests and from the margins of a river and a flooded forest stream.

Discussion.

Although the holotype of Hydrodessus biguttatus was not found, a paratype specimen was examined and compared with the holotype and other material of Hydrodessus fragrans . The Hydrodessus biguttatus paratype is a male, and is dissected, but the genitalia are not with the specimen. Nevertheless, the specimen agrees well with specimens of Hydrodessus fragrans . In particular, these specimens all have the apices of the elytra distinctly dehiscent and the apex of the metatrochanter minutely but distinctly bispinous with a small spine at the dorsal apex and a slightly smaller spine at the ventral apex. Spangler (1985) diagnosed Hydrodessus fragrans from Hydrodessus biguttatus mainly on coloration and punctation, but these differences are well within the typical range of variation of species of Hydrodessus . For this reason, Hydrodessus fragrans Spangler, 1985 is placed as a junior synonym of Hydrodessus biguttatus (Guignot, 1957), syn. n.

This species, though widespread, is rarely collected and has not been collected in long series.

Specimens.

Holotype of Hydrodessus biguttatus not examined. Holotype of Hydrodessus fragrans examined, male in USNM labeled, "GUYANA: Mazaruni- Potaro District Takutu Mountains 6°15'N, 59°5'W 16 December 1983/ EARTHWATCH Research Expedition: P. J. Spangler & W. E. Steiner Collectors/ At blacklight in forest clearing near streams/ HOLOTYPE Hydrodessus fragrans PJ Spangler [red label]/ BLNO 003803 [blue label with black line around margin]."

Other non-type specimens examined (6 specimens): Brazil, Para, Cachimba, 25.6°S 49.3°W, 1 Oct 1955, Pereira (1, MZSP, paratype of Hydrodessus biguttatus ); São Paulo, Dona Antonio, 22.7°S 47.7°W, 14 Mar 1979, C.R. Owen (1, USNM). Guyana, Mazaruni-Potaro District, Takutu Mountains, 6.25°N, 59.083°W, 14 Dec 1983, blacklight in forest clearing near streams, P.J. Spangler, W.E. Steiner (2, USNM, including 1 paratype of Hydrodessus fragrans ). Suriname, Sipaliwini District, Camp 1, on Kutari River, 2.175°N, 56.787°W, 22 Aug 2010, flooded forest stream, 228m, Short, Kadosoe (1, KUNHM, SEMC0913238). Venezuela, Amazonas, Cerro de la Neblina, basecamp, 0.833°N, 66.167°W, 27 Jan 1985, netted along margins of Rio Baria, 140m, P.J. Spangler, P.M. Spangler, R. Faitoute, W. Steiner (2, USNM).