Hydrodessus ducke, Benetti & Michat & Hamada, 2020

Benetti, Cesar J., Michat, Mariano C. & Hamada, Neusa, 2020, Hydrodessus ducke sp. n. and new records of other species of the genus (Coleoptera, Dytiscidae, Bidessini), Zootaxa 4743 (1), pp. 47-60 : 48-49

Hydrodessus ducke sp. n.

( Figs 1, 2 , 5, 6 , 9–11 , 15 )

Type locality. Brazil: Amazonas State , Manaus County, “Reserva Florestal Adolpho Ducke, Igarapé Bolívia ” (02º59’14”S 059º56’30”W) .

Type material. Holotype ♂: Brazil: Amazonas State , Manaus County, “Reserva Florestal Adolpho Ducke, Igarapé Bolívia ” (02º59’14”S 059º56’30”W); 65 m a.s.l.; 25ºC temp., 14 conductivity, 4.9 pH, sandy stream, forest; 06.xi.2008; leg. U. Neiss, F. Sales, P. Vilela ( INPA). [red holotype label] . Paratypes (7): same data as holotype, except 14.viii.2002; leg. C. Benetti [red paratype label]; “ Reserva Florestal Adolpho Ducke , Igarapé do Ipiranga ” (02º59’36”S 59º53’25”W); 68 m a.s.l.; 02.vii.2015; leg. A. Pes, G. Gomes, P. Barcelos, W. Xavier ( INPA, 3 ♂) [red paratype label] .

Diagnosis. Hydrodessus ducke sp. n. can be distinguished from other Hydrodessus species by the following combination of characters: body size (total length: 2.65–2.8 mm); body outline only slightly discontinuous between pronotum and elytron; coloration evenly dark red-brownish ( Figs 1, 2 ); lateral elytral carina extending to about half length of elytron ( Fig. 5 ); prosternal process broad with lateral margins subparallel and apex truncate ( Fig. 6 ); metaventrite carinae and metacoxal lines approximately continuous ( Fig. 6 ); median lobe in lateral aspect broadly and evenly curved with rounded apex ( Fig. 9 ), in ventral aspect with lateral margins parallel and apex strongly incised medially ( Fig. 10 ).

Description. Habitus ( Figs 1, 2 ). Body shape oval, broad, apically slightly acuminate; lateral body outline only slightly discontinuous between pronotum and elytron; elytra apically pointed, slightly dehiscent.

Measurements. TL = 2.65–2.8 mm, GW = 1.35–1.45 mm, PW = 1.15–1.25 mm, HW = 0.75–0.8 mm, EW = 0.4–0.45 mm, TL/GW = 1.9–2.0, HW/EW = 1.69–1.83.

Coloration ( Figs 1, 2 ). Head, pronotum and elytra evenly dark red-brownish; antennae, palps and legs redbrownish; venter evenly dark red-brownish with abdominal ventrites slightly lighter.

Sculpture and structure. Head broad, short, anterior clypeal margin rounded; surface shiny, covered with fine punctures; microreticulation not visible at 100x; eyes relatively large. Pronotum with lateral margins curved, widest at posterior margin; greatest width of pronotum narrower than elytral base; lateral bead fine; surface shiny with distinctive but weakly marked punctures, coarser than on head; microreticulation not visible at 100x. Elytra elongate, apically pointed and slightly dehiscent, lateral margins evenly curved, greatest width at basal third; lateral carina distinct, extending a little beyond elytral half ( Fig. 5 ); surface shiny with weakly marked punctures, with short setae mainly on apical third; microreticulation not visible at 100x. Ventral surface shiny, densely punctate; microreticulation not visible at 100x. Prosternum medially tectiform and setose; prosternal process broad, lateral margins subparallel, apex truncate ( Fig. 6 ). Metaventral platform not strongly constricted anteriorly; metaventrite with anterior process broad, truncate; metaventrite carinae well-marked, somewhat divergent posteriorly, ending near anterior ends of metacoxal lines (metaventrite carinae and metacoxal lines approximately continuous) ( Fig. 6 ). Legs shiny, finely punctate; metacoxal lines broadly separated, slightly sinuate, divergent anteriorly but anterior ends somewhat converging; metatrochanter somewhat offset, apically broadly pointed; pro- and mesotibiae moderately slender; metatibia with distinctive posteroapical brush of setae. Abdomen shiny, weakly punctate; ventrite VI apically somewhat narrowly rounded.

Male genitalia. Median lobe in lateral aspect ( Fig. 9 ) broadly and evenly curved, basal region broad, medial and distal portions relatively slender, apex rounded; in ventral aspect ( Fig. 10 ) broad, lateral margins subparallel, slightly narrowed at basal portion; apex with lateral angles curved, strongly incised medially. Lateral lobes ( Fig. 11 ) broad basally, distally gradually narrowed, apex rounded with series of short setae.

Sexual dimorphism. Male pro- and mesotarsi I–III slightly broader than in female, ventrally with several large adhesive setae; posteroapical brush of setae on male metatibiae composed of adhesive setae.

Etymology. This species is named after the “Reserva Florestal Adolpho Ducke” where the type locality is located. The name is a noun in the nominative singular standing in apposition.

Distribution. Northern Brazil, currently only known from the state of Amazonas ( Fig. 15 ).

Habitat. Specimens were collected in shaded forest streams, with sandy bottom and root as substrate, at 68–107 m a.s.l.

Taxonomic remarks. Hydrodessus ducke sp. n. is similar to H. continuus Miller, 2016 , H. concolorans Miller, 2016, H. brasiliensis ( Guignot, 1957) and H. octospilus ( Guignot, 1957) in having the lateral elytral carina long (more than 1/4 elytral length), prosternal process broad and metaventral platform not strongly constricted anteriorly, but can be differentiated from these species in the pronotum with lateral margins curved, widest at posterior margin, and in the shape of the male genitalia. The new species differs from H. continuus in having the metacoxal lines slightly divergent anteriorly, the lateral elytral carina extending to about half length of elytron and the prosternal process with lateral margins subparallel and not constricted, whereas H. continuus has the metacoxal lines broadly divergent anteriorly, the lateral elytral carina short, about 1/3 length of elytron, and the prosternal process widest at anterior angles, medially constricted. From H. concolorans, H. brasiliensis and H. octospilus the new species differs in having the metacoxal lines continuous with metaventrite carinae (metacoxal lines intersecting metaventrite carinae at distinct angle in the other species). Hydrodessus ducke sp. n. also differs from H. concolorans in having the greatest width of pronotum only slightly smaller than the greatest width across elytra (greatest width of pronotum considerably smaller than greatest width across elytra in H. concolorans) and in the length of elytral carina (about half of elytron length in the new species and 1/3 of elytron length in H. concolorans). Hydrodessus brasiliensis can be differentiated from the new species also in having the prosternal process distinctly constricted medially with prominent anterolateral lobes (prosternal process lacking lateral lobes and not constricted medially in the new species). Hydrodessus octospilus differs from H. ducke sp. n. in coloration, with head and pronotum orange-red and elytron with large, very diffuse pale areas anteriorly, subapically and at apex, whereas the new species has the head, pronotum and elytra evenly dark red-brownish.

Figures

FIGURE 15. Hydrodessus species, distributions. Star: H. ducke sp. n.; circle: H. disjunctus; square: H. surinamensis; triangle: H. laetus; hexagon: H. morsus; inverse triangle: H. palus. Open symbols (previous records), solid symbols (new records).

FIGURES 1–4. Hydrodessus species. (1–2) H. ducke sp. n., holotype male; (3–4) H. latotibialis, male from Brazil. (1, 3) habitus, dorsal aspect; (2, 4) habitus, ventral aspect. Scale bars = 1 mm.

FIGURES 5–8. Hydrodessus species. (5–6) H. ducke sp. n., holotype male; (7–8) H. latotibialis, male from Brazil. (5, 7) right elytron, lateral aspect; (6, 8) prosternal process, metaventrite and metacoxal lobes, ventral aspect. Scale bars = 1 mm.

FIGURES 9–14. Hydrodessus species. (9–11) H. ducke sp. n., holotype male; (12–14) H. latotibialis, male from Brazil. (9, 12) median lobe, right lateral aspect; (10, 13) median lobe, ventral aspect, in detail also a ventral aspect but perpendicularly onto the apex; (11, 14) right lateral lobe, right lateral aspect. Scale bars = 0.2 mm.