Hydrodessus siolii J. Balfour-Browne, 1953

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 : 105-108

Taxon classification Animalia Coleoptera Dytiscidae

Hydrodessus siolii J. Balfour-Browne, 1953 Figs 31, 43

Hydrodessus siolii J. Balfour-Browne, 1953: 56; Young 1967: 80; 1969: 2; 1970: 158; Spangler 1985: 88; Biström 1988: 37; Nilsson 2001: 236.

Type locality.

Brazil, Pará, Rio Cupari, Igarapé Ingatuba.

Diagnosis.

Hydrodessus siolii is a distinctive species with a pale head and pronotum and the elytra dark brown with the lateral margin yellow with distinctive, well defined yellow maculae (Fig. 31A). There is a prominent yellow macula on the elytral disc near the suture subbasally (Fig. 31A). There are a semiconnected pair of maculae at about 2/3 length of elytra (Fig. 31A). In some specimens the lateral macula is connected with the yellow lateral margin. Also, the elytral apex is yellow (Fig. 31A). The lateral elytral carina is absent (Fig. 31B). The prosternal process is elongate oval with the lateral margins slightly constricted medially (Fig. 31C). The prosternal process is elongate oval with the lateral margins somewhat constricted medially (Fig. 31C). The metaventrite carinae are indistinct and mainly marked by impunctate lines that are strongly divergent posteriorly (Fig. 31C). The male median lobe in lateral aspect is basally triangular (Fig. 31D). The apical portion is slender and evenly curved to a slender, narrowly rounded apex (Fig. 31D). In ventral aspect the median lobe is bilaterally symmetrical, apically convergent to elongate, slender, pointed apex (Fig. 31E). The lateral lobe is relatively slender, curved medially with the apical 1/3 relatively straight and slender to rounded apex (Fig. 31F). The species is perhaps most similar to Hydrodessus fasciatus in body shape and structure, but that species has a different color pattern and the male genitalia are distinctive in each species.

Description.

Measurements. TL = 2.7-3.1 mm, GW = 1.3-1.4 mm, PW = 1.1-1.2 mm, HW = 0.8-0.9 mm, EW = 0.4-0.5 mm, TL/GW = 2.1-2.2, HW/EW = 1.9. Body shape elongate, apically rounded, lateral outline discontinous between pronotum and elytron (Fig. 31A).

Coloration (Fig. 31A). Head and pronotum yellow. Elytron brown-yellow with diffuse yellow maculae anteromedially, medially and along margins anteriorly, mediolaterally, and at apex (Fig. 31A). Antennae, palps and legs yellow. Ventral surfaces yellow.

Sculpture and structure. Head moderately elongate; anterior clypeal marign broadly rounded; surface shiny, nearly impunctate; eyes large. Pronotum broadest slightly anterior of middle, lateral margins broadly curved (Fig. 31A); lateral bead fine; surface shiny, covered with moderately large, distinctive punctation. Elytra elongate, apically rounded (Fig. 31A); lateral carina absent, slight rounding of elytron near humeral angle (Fig. 31B); surface shiny, covered with moderately large, distinctive punctation. Prosternum medially rounded and setose; prosternal process moderately slender, elongate, lateral margins subparallel, widest subapically, apex rounded, longitudinally somewhat excavated (Fig. 31C). Metaventrite with anterior process slender, short, apically narrowly rounded; metasternal carinae distinct only anteriorly along margins of process, extending posteriorly in broadly divergent rounded margins, terminating near anterior ends of metacoxal lines (Fig. 31C); other surfaces covered with moderately large, distinct punctures. Legs with most surfaces shiny, impunctate; pro- and mesotibiae slender; metatibia with posteroapical brush of setae distinctive; metatrochater distinctly offset, apically rounded; metacoxa with surface shiny, covered with moderately large, distinctive punctation; metacoxal lines elongate, relatively closely approximated and subparallel, only slightly diverging anteriorly (Fig. 31C). Abdomen shiny, covered with distinctive punctures; ventrite VI apcially broadly rounded.

Male genitalia. Median lobe bilaterally symmetrical, in lateral aspect gently curved, curvature more pronounced basally, basal region broad, apical portion slender throughout length, apex slender and pointed (Fig. 31D); in ventral aspect slender, lateral margins evenly convergent to middle, then slightly constricted and apically slender to pointed apex (Fig. 31E). Lateral lobe moderately broad basally, elongate slender apically, apex rounded, with series of setae along dorsal margin (Fig. 31F).

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. Females much more finely and densely punctate on all surfaces than males.

Variation. Specimens examined vary somewhat in the extend of maculation on the dorsal surface.

Distribution.

This species is known from central Brazil and southern Venezuela (Fig. 43).

Habitat.

This species was collected from "margem esquedra, entre detrito fibrosito" ( Balfour-Browne 1953), or the "left bank, between fibrous detritous." Specimens have also been collected along a sandy forest stream in marginal leaf pack.

Discussion.

The holotype (in BMNH) was not examined, but the male paratype (of one male and two female paratypes, Balfour-Browne 1953), which is now in the FSCA, was examined. Based on the description and the paratype examined, the identity of this species is clear.

Specimens.

Holotype not examined. Non-type specimens examined, 64 total. Brazil, Aldeia Aracu-Igarape, Gurupi-Umi, 50km E Caninde, 2°35'S 46°05W, 1-31 May 1963, B. Malkin (2, FSCA); Brazil, Pará, Boca Igarape Ingatuba, 3.723°S 55.404°W, 22 Oct 1948, H. Sioli (1, FSCA, paratype). Venezuela, Amazonas, Communidad Caño Gato, on Rio Sipapo, 4.981°N, 67.739°, 16 Jan 2009, along stream, 95m, Short, Miller, Camacho, Joly and García (61, KUNHM, MIZA, MSBA, USNM, museum numbers in Table 1).