Hydrodessus rattanae Makhan, 1994: 118

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 : 104-105

Taxon classification Animalia Coleoptera Dytiscidae

Hydrodessus rattanae Makhan, 1994: 118 Figs 30, 51

Hydrodessus rattanae Makhan, 1994: 118; Biström 1988: 37; Nilsson 2001: 236.

Type locality.

Suriname, District Brokopondo, Brownsweg.

Diagnosis.

Hydrodessus rattanae is robust and broadly rounded with a distinctive dorsal pattern of maculae and fasciae (Fig. 30A). The head and pronotum are yellow (Fig. 30A). The elytra are brown with yellow lateral margins and large, well-defined maculae subbasally, apically and at about 2/3 length of elytra (Fig. 30A). Specimens do not have a lateral elytral carina, the epipleural carina extends nearly straight from the humeral angle (Fig. 30B). The prosternal process is elongate oval with the apex broadly pointed (Fig. 30C). The metaventrite carinae are distinctive and moderately divergent posteriorly (Fig. 30C). The male median lobe is basally narrowly triangular (Fig. 30D). The apical portion is long and nearly evenly curved with the apex narrow (Fig. 30D). In ventral aspect the median lobe is bilaterally symmetrical with the lateral margins narrowed to narrowly rounded apex (Fig. 30E). The lateral lobe is elongate-triangular with a long series of setae along the dorsal margin (Fig. 30F). This species is similar to Hydrodessus laetus in coloration, overall shape, lack of lateral elytral carinae, shape of the prosternal process and metasternum and other features. The male genitalia are diagnostic (Figs 30 D–F). Hydrodessus rattanae is more robust, not as attenuate posteriorly and the color pattern is a little different (Fig. 30A). The metacoxal lines and regions mediad to the metacoxae are different, too (Fig. 30C). In Hydrodessus rattane the metacoxal lines are shorter, somewhat more divergent anteriorly and there are deep, longitudinal grooves along the medial margin of each metacoxal lines (Fig. 30C) that are missing in Hydrodessus laetus (Fig. 22C).

Description.

Measurements. TL = 2.6-2.7 mm, GW = 1.3-1.4 mm, PW = 1.1-1.2 mm, HW = 0.8-0.9 mm, EW = 0.5 mm, TL/GW = 1.9-2.0, HW/EW = 1.7-1.8. Body shape broad, posteriorly broadly, outline discontinous between pronotum and elytron (Fig. 30A), body somewhat depressed.

Coloration (Fig. 30A). Head and pronotum orange. Elytra fasciate, brown to brown-red with large irregular yellow regions transversely near anterior margin and medially, apex yellow, macula distinctly delimited, medial macula often separated into broad lateral marginal macula and smaller macula near suture (Fig. 30A). Antennae, palps and legs yellow. Ventral sclerites yellow, black along some sutures.

Sculpture and structure. Head broad, anteriorly broadly curved; surface shiny with fine punctures; eyes large. Pronotum with lateral margins broadly rounded, widest slightly anterior to middle (Fig. 30A); lateral bead fine; surface shiny with fine, indistinct microreticulation, covered with fine punctures. Elytra broad, lateral margins broadly curved, apically broadly; lateral carina absent, elytral epipleural carina extends directly posteriorly from humeral angle (Fig. 30B); surface with fine microreticulation throughout and covered with fine punctures. Prosternum medially tectiform; prosternal process broad, subrectangular, lateral margins subparallel, slightly constricted medially, apically broadly pointed, process medially deeply and broadly excavated (Fig. 30C). Metaventrite with anterior process short and broad, medially distinctly excavated, slightly constricted subapically, apically subtruncate; metasternal carina distinctive, straight and diverging posteriorly, posterior half indistinct, low and rounded, terminating at anterior ends of metacoxal lines (Fig. 30C); surfaces covered with fine punctation. Legs with surfaces shiny, weakly and indistinctly punctate; metatibia with posteroapical brush of setae distinctive; pro- and mesotibiae moderately broad; metatrochanter not strongly offset, elongate, apically narrowly rounded; metacoxa covered with fine punctation; metacoxal lines robust, well marked, narrowly separated, subparallael but slightly divergent anteriorly, longitudinally distinctly grooved mediad to metacoxal lines (Fig. 30C). Abdomen covered with fine punctation; apex of VI rounded.

Male genitalia. Median lobe bilaterally symmetrical, in lateral aspect robust, broadly and evenly curved, basal portion small and subtriangular, apical portion broad to rounded apex (Fig. 30D); in ventral aspect broad, lateral margins subparallel, apically slightly curved, and apex broadly rounded (Fig. 30E). Lateral lobe slender, elongate, without broad basal region, apex straight, evenly narrowed to rounded apex (Fig. 30F).

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. Specimens exhibit some minor variation in the extend of the maculae on the elytron.

Distribution.

This species is known only from a couple localities in Suriname (Fig. 51).

Habitat.

A series of specimens was collected along the margins of a forest creek.

Discussion.

This species and Hydrodessus laetus are similar to each other and very different from many other species of Hydrodessus in the shape of the lateral margins of the elytron. The epipleural carina (between the epipleuron and dorsal surface of the elytron) extends posteriorly directly from the humeral angle. There is no other lateral carina. It remains to be seen whether these species are together monophyletic with the other members of Hydrodessus .

Specimens.

Holotype: ♂ in NZCS labeled, "Suriname District Brokopondo Brownsweg 7.8.1984 leg. D.Makhan/ Hydrodessus rattanae det. D. Makhan 1994 / Holotype [red label]." Other material examined, Suriname, Sipaliwini Dist, Tafelberg Summit nr Austustus Cr Camp, 3.933'N 56.183'W, 22 Aug 2013, forest creek margins, 600m, Short and Bloom (5, KUNHM, see accession numbers in Table 1).