Hydrodessus octospilus (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 : 94-97

Taxon classification Animalia Coleoptera Dytiscidae

Hydrodessus octospilus (Guignot, 1957) Figs 26, 48

Brinckius octospilus Guignot, 1957: 39.

Hydrodessus octospilus , Young 1969: 2; 1970: 157; Spangler 1985: 89; Biström 1988: 37; Nilsson 2001: 236.

Hydrodessus robinae Spangler, 1985: 85; Biström 1988: 37; Nilsson 2001: 236.

Type locality.

Brinckius octospilus , Brazil, Para Province, Cachimbo. Hydrodessus robinae , Guyana, Mazaruni-Potaro District, Takutu Mountains, 6°15'N 59°5'W.

Diagnosis.

This is a relatively compact species with the dorsal coloration ranging from red to red-brown, sometimes with larger, indistinct pale areas or smaller, more distinctive pale regions (Fig. 26A). The lateral elytral carina is well-developed, extending beyond half the length of the elytron and with a distinct, impressed interruption at about half its length (Fig. 26B). The prosternal process is broad with the lateral margins subparallel and the apex broadly truncate (Fig. 26C). The metaventrite carinae are very well developed, not strongly constricted anteriorly, and evenly divergent posteriorly (Fig. 26C). The male median lobe in lateral aspect is triangular basally with the apical portion somewhat evenly curved with the apex subapically constricted and pointed (Fig. 26D). In ventral aspect the male median lobe is relatively broad with the lateral margins evenly convergent to a pointed apex (Fig. 26E). The lateral lobe is relatively narrow with the lateral margins straight and evenly convergent to the rounded apex (Fig. 26F).

Description.

Measurements. TL = 2.9 mm, GW = 1.4 mm, PW = 1.2 mm, HW = 0.9 mm, EW = 0.5 mm, TL/GW = 2.1, HW/EW = 1.6-1.7. Body shape moderately robust, apically pointed, lateral margins only somewhat discontinuous between pronotum and elytron (Fig. 26A).

Coloration (Fig. 26A). Head and pronotum orange-red. Elytron with base color red, with large, very diffuse pale areas anteriorly, subapically and at apex. Antennae and palps orange. Legs orange-red. Venter yellow-brown, red medially on surfaces, some areas nearly black including portions of prosternal and mesosternal processes and basal abdominal sutures.

Sculpture and structure. Head broad, anterior clypeal margin broadly curved; surface shiny with few, sparse minute punctures; eyes large. Pronotum subcordate, widest anterior of middle (Fig. 26A); lateral bead fine and continuous; surface shiny, covered with minute punctures, larger along anterior margin. Elytra moderately elongate, apically narrowly rounded (Fig. 26A); lateral carina distinctive and prominent, extending well beyond ½ length of elytron, slightly but distinctly impressed and interrupted near half its length; surface covered with minute punctures. Prosternum medially carinate and setose; prosternal process broad, with prominent anterolateral angles, lateral margins subparallel, apex broadly truncate, longitudinally strongly impressed (Fig. 26C). Metaventrite with anterior process moderately broad, laterally rounded, apex slightly truncated, medially flat; metasternal carinae flattened and broad, straight and divergent to posterior margin, terminating near anterior ends of metacoxal lines (Fig. 26C). Legs with most surfaces covered with fine punctures; metatibia with distinctive brush of dense, elongate setae on postero-apical surface; pro- and mesotibiae moderately broad; metatrochanter not strongly offset, apically pointed; metacoxa evenly covered with fine punctures; metacoxal lines broadly separated, somewhat sinuate and slightly divergent anteriorly (Fig. 26C). Abdomen shiny, evenly covered with fine punctures; apex of VI broadly pointed.

Male genitalia. Median lobe bilaterally symmetrical, in lateral aspect robust, moderately curved, basal portion broad, but not large, apical portion more straight, apex narrowed to slightly curved, nearly pointed apex (Fig. 26D); in ventral aspect broad, lateral margins broadly rounded, apex narrowed to narrowly rounded apex (Fig. 26E). Lateral lobe broad basally, apical portion elongate triangular, lateral margins straight and evenly convergent to rounded apex, with seta along apical margin (Fig. 26F).

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. Female with abdominal ventrite VI slightly impressed on each side, apicomedially flattened and pointed; male with VI apically rounded, not impressed.

Variation. Specimens vary in extent of the dorsal maculae and intensity of dorsal coloration from nearly immaculate to distinctly maculate with larger pale regions.

Distribution.

This species is known from Guayana and southern Venezuela to Brazil and south to Paraguay (Fig. 48).

Habitat.

Hydrodessus octospilus has been collected from blacklights and forested creek and river margins.

Discussion.

Examination of the male holotype specimens of Hydrodessus octospilus and Hydrodessus robinae indicates that these two names refer to the same species. Spangler (1985) erected Hydrodessus robinae in part based on it having a longer lateral elytral carina compared with Hydrodessus octospilus , but this is really not the case. The type specimen of a Hydrodessus octospilus has the lateral carina extending distinctly beyond half the length of the elytron similar to the type of Hydrodessus robinae . Also, the male genitalia of the two holotypes are extremely similar. Two female specimens from Paraguay (FSCA) are here assigned to this species. Though this is well south of the range of other, more definite Hydrodessus octospilus , they do appear to be Hydrodessus octospilus .

Specimens.

The Hydrodessus octospilus male holotype in MZSP was examined, labeled, "Type [red label with black line border]/ Brasilien, Para Cochimbo X.1955 Pereira [black line border]/ F. Guignot det., 1956 Brinckius octospilus n.sp. Type ♂ [handwritten]/ 31904."

The Hydrodessus robinae male holotype in USNM was examined, labeled, "GUYANA: Mazaruni- Potaro District Takutu Mountains 6°15'N, 59°5'W 17 December 1983/ EARTHWATCH Research Expedition; P.J. Spangler. R.A. Faitoute/ HOLOTYPE Hydrodessus robinae PJ Spangler [red label]/ BLNO 003806 [blue label with black line around margin]."

Additional non-type material examined (15 total). Guyana, Mazaruni-Potaro District, Takutu Mountains, 6.25°N, 59.083°W, 17 Dec 1983, blacklight in forest clearing near streams, P.J. Spangler, W.E. Steiner (1, USNM, Hydrodessus robinae paratype); Region IX, road to Parabara, creek crossing at Mushal Wao, 2.161°N, 59.292°W, 1 Sep 2013, creek margins, 268m, Short, Isaacs, Salisbury (8, KUNHM, collection number in Table 1). Paraguay, Paraguari, Arroyo Minas, Parque Nacional Ybycui, 25 Jul 1981, R. Cave (1, FSCA); same except 25kmb SE Ybycui, Arroyo Minas in Parque Nacional Ybycui, 24 Jan 1981, R.D. Cave (1, FSCA). Venezuela, Amazonas, Cerro de la Neblina, basecamp, 0.833°N, 66.167°W, 20 Feb 1985, netted along margins of Rio Baria, 140m, P.J. Spangler, P.M. Spangler, R. Faitoute, W. Steiner (2, USNM); same except 6 Feb 1985, blacklight on bank of Rio Baria, W.E. Steiner (1, USNM); same except 27 Jan 1985 (1, USNM).