Hydrodessus angularis Young, 1970

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 : 57-59

Taxon classification Animalia Coleoptera Dytiscidae

Hydrodessus angularis Young, 1970 Figs 8, 35, 46

Hydrodessus angularis Young, 1970: 155; Spangler 1985: 88; Biström 1988: 37; Nilsson 2001: 236.

Type locality.

Suriname, Carolina Creek, 10km S Zanderij.

Diagnosis.

This is a very distinctive species which is dorsally nearly concolorous red (Fig. 8A1,A2) except some specimens have the head and pronotum lighter orange and some specimens have poorly defined pale regions basally and subapically on the elytron. The lateral elytral carina is sharp and long, extending more than 3/4 length of the elytron (Fig. 8B). Specimens are robust with the lateral margins broadly rounded (Fig. 8A). Many specimens (not all) have the anterolateral angles of the pronotum conspicuously flattened and produced laterally into distinct, broad angle (Fig. 8A1). The anterior clypeal margin is beaded and somewhat projecting. The prosternal process is broadly quadrate and apically broadly trunctate (Fig. 8C). The metaventrite carinae are distinctive and posteriorly divergent (Fig. 8C). The male median lobe is basally triangular with the apical portion curved basally and apically approximately linear with the apex slight curved dorsad and narrowly rounded (Fig. 8D). The median lobe in ventral aspect is moderately broad with the lateral margins broadest submedially and evenly convergent to broadly pointed apex (Fig. 8E). The lateral lobe is very broad with the lateral margins approximately convergent to rounded apex (Fig. 8F).

Description.

Measurements. TL = 2.9-3.2 mm, GW = 1.4-1.5 mm, PW = 1.3 mm, HW = 0.9 mm, EW = 0.5-0.6 mm, TL/GW = 2.0-2.1, HW/EW = 1.6-1.7. Body robust, broad, lateral margin only slightly discontinous between pronotum and elytron (Fig. 8A).

Coloration (Fig. 8A). Head and pronotum yellow. Elytra brown to yellow or red-brown, with subapical, small, triangular macula and apex yellow in many specimens with other specimens evenly brown. Antennae and palps yellow to yellow brown. Legs yellow. Venter yellow to orange.

Sculpture and structure. Head broad, relatively short, apically with clypeal margin projecting, medially broadly truncate and finely beaded; surface with inconspicuous, fine punctures; eyes moderately large. Pronotum with lateral margins broadly curved, greatest width near middle (Fig. 8A), some specimens with lateral margins more strongly flattened and distinctly angulate anterolaterally (Fig. 8A1); lateral bead fine anteriorly, slightly expanded near posterolateral angle; surface shiny with fine punctation medially, irregularly punctate to rugulose laterally. Elytra broad, lateral margins subparallel in anterior half; lateral carinae very well developed and prominent, extending more than ¾ length of elytron (Fig. 8C); elytral apex with slight constriction subapically; surface covered with fine punctures. Prosternum medially slightly carinate; prosternal process very broad, subquadrate, lateral margins subparallel, but widest at anterior margin, apex broadly truncate to broadly concave, medially strongly impressed (Fig. 8C). Metaventrite with metasternal process well developed, apically truncate, subapically constricted, medial surface slightly excavated, carinae well-developed, long, divergent posteriorly across metasternum, ending near anterior ends of metacoxal lines (Fig. 8C); Metaventrite covered with fine punctures. Legs with surfaces covered with fine punctures; pro- and mesotibiae moderately broad; metatibia with posteroapical brush of setae; metacoxa covered with fine punctures; metacoxal lines broadly separated, subparallel, but slightly curved and anteriorly somewhat divergent (Fig. 8C). Abdomen covered with fine punctures.

Male genitalia. Median lobe bilaterally symmetrical, in lateral aspect strongly curved medially, with base broad and subtriangular, apical portion more straight, with dorsal and ventral margins slightly expanded, narrowing to slender, narrowly rounded apex (Fig. 8D); in ventral aspect broad, lateral margins broadly curved, apically evenly convergent to pointed apex (Fig. 8E). Lateral lobe very broad basally, elongate, margins approximately evenly convergent to narrowly rounded apex which has small cluster of setae (Fig. 8F).

Female genitalia. Gonocoxosternite broad, posterolateral margin broadly curved, medial margin slightly concave, anterior portion small, lobate (Fig. 35). Gonocoxa with apical portion broadly triangular, apically narrowly rounded, anterior apodeme as long as apical portion and sinuate (Fig. 35). Bursa short and broad; spermathecal duct extremely long and slender, expanding near receptacle which is small; spermatheca elongate and twisted, without spermathecal spine; fertilization duct extremely long, slender, and coiled (Fig. 35).

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

Variation. The apical elytral maculae are indistinct in many specimens and are most conspicuous in teneral specimens. The most conspicuous variation is the degree of angulation of the lateral pronotal margins. Individuals from Suriname have the lateral pronotal margins strongly flattened and distinctly angulate (Fig. 8A1). Specimens from farther west, including Venezuela, have the lateral margins less strongly angulate (Fig. 8A2). The Suriname specimens also have the anterior margin of the clypeus more strongly concave that those specimens farther west. The specimens agree in other characters including the shape of the prosternal process, metasternum, and metacoxae and the shape of the male genitalia such that the variation in the lateral pronotal margin is here regarded as intraspecific variation.

Distribution.

Hydrodessus angularis is known from Amazonas, Brazil through Guyana and Suriname to southern Venezuela (Fig. 46).

Habitat.

Specimens have been collected from along a river margin, in a large sandy creek, a muddy oxbow pond, in detrital pools by a forest stream, and from lights at night. The species appears to be mainly associated with margins of forest rivers.

Discussion.

Although the holotype of this species (in Rijksmuseum van Natuurlijke Historie, Leiden) was not examined, there is little doubt as to the identity of the species. That said, many specimens do not have the anterior angles of the pronotum nearly as angulate as others. In some of these specimens the anterior margin of the clypeus is not as strongly margined. The more angulate specimens are generally found in the eastern part of the range. The male genitalia are identical, and other features, such as the well-marked lateral elytral carina, the shape of the prosternal process, metaventrite carinae, and metacoxae are also the same. Even so, a greater sampling may eventually reveal that more than one species is actually involved.

Specimens.

Holotype not examined. Other non-type specimens examined (84 total): Brazil; Amazonas, Ig.Tarumazinho, 46km N Manaus, 2.339°S 60.029°W, 6 Feb 1979, O. Flint (1, USNM). Guyana; Mazaruni-Potaro District, Takutu Mountains, 6.25°N, 59.083°W, 18 Dec 1983, blacklight forest clearing near streams, Earthwatch Research Expedition, P.J Spangler and W.E. Steiner (2, USNM). Suriname; Sipaliwini District, Camp 1, Upper Palumeu, 2.477°N, 55.629°W, 14 Mar 2012, large sandy creek, 275m, A. Short (4, KUNHM); Sipaliwini District, CSNR: near Kappel airstrip, 3.792°N, 56.150°W, 12 Aug 2013, uv light trap, 320m, A.E.Z. Short (7, KUNHM). Venezuela; Territorio Federal Amazonas, Cerro de la Neblina, basecamp, 0.833°N, 66.167°W, 21 Feb 1985, muddy oxbow pond, rainforest clearing, 140m, W.E. Steiner (6, USNM); Territorio Federal Amazonas, Cerro de la Neblina, basecamp, 0.833°N, 66.167°W, 20 Feb 2985, seined from rocks in rapids of Rio Baria, 140m, P.J. Spangler, P.M. Spangler, R. Faitoute and W. Steiner (23, USNM); Territorio Federal Amazonas, Cerro de la Neblina, basecamp, 0.833°N, 66.167°W, 20 Feb 2985, netted along margins of Rio Baria, 140m, P.J. Spangler, P.M. Spangler, R. Faitoute and W. Steiner (40, USNM); Bolivar State, Gran Sabana, Pauji, Esmeraldes, 4.471°N, 61.593°W, 16 Jul 2010, detrital pools by forested stream, 867m, Short, Tellez and Arias (1, KUNHM). KUNHM catalog numbers in Table 1.