Tritonus complanatus, Short, Andrew Edward Z., 2008

Short, Andrew Edward Z., 2008, Revision of the Afrotropical genus Tritonus Mulsant (Coleoptera: Hydrophilidae), Zootaxa 1855, pp. 41-55 : 45-48

Tritonus complanatus sp.n.

( Figs. 1–2 , 4 , 6–7 , 9–10 , 13 , 21 )

Type Material. Holotype (male): “ MADAGASCAR (144): Antsiranana/ Andapa: R. Masiaposa (Crossing R.N./ 3b at km 5–6) about & km upstr. Road/ bridge, 700 m, 10.xi.2001 / Gerecke & Goldschmidt” ( NMW). Paratypes (47): MADAGASCAR: Antananarivo Province: Manakambahiny, 15.ii.1990, W.E. Steiner, leg., “in seepage over exposed granite cliff face” (3, NMNH, MCZ); Antsiranana Province: Andapa, right affl. R. Ambendrana, downstream of large cascade, 660m, 11.xi.2002, Gerecke & Goldschmidt, leg., 147 (4, NMW); Andapa, “R. Masiaposa (Crossing R. N. 3b at km 5–6) about & km upstream road bridge”, 700m, 10.xi.2001, Gerecke & Goldschmidt, leg., 144 (14, FHC, KSEM, NMW, NMPC); Mt. D’Ambre Forest Reserve, stream at Grand Cascade, 617m, 13.xi.1986, J.T. & D.A. Polhemus, CL2278 (1, CAS); Antsabe, 13.6093°S, 48.7212°E, 23.xi.2004, M. Balke, leg. (9, KSEM, NHML); Fianarantsoa Province: Andrambouato, large cascade 3km E. of village, 820m, 20.viii.2001, Gerecke & Goldschmidt, leg., 0 37 (1, NMW); Abohimahasoa, village hotel Riandrano, alt. 1208m, 21 6.203’S, 47 12.144’E, 6.v.2006, “hygropetric surface next to waterfall”, J. Bergsten, leg., “Loc. P37A” (4, NHML); Andringitra National Park, Riambavy river (Female) cascade, 1739m, 8.c.2006, 22 8.761’S, 46 53.495’E, “wet rock surfaces next to high waterfall”, J. Bergsten, leg., “Loc. P39A” (1, NHML); Tananarive Province: Tananarive, waterfall and seeps nr. Queen’s palace, 1310m, 24.x.1986, J.T & D.A. Polhemus, CL2233 (10, CAS).

Diagnosis. The large size and broadly oval, nearly circular body form serve to easily distinguish this species from all other members of the genus. Tritonus crenulatus is somewhat similar in shape, but is distinctly smaller and possesses strongly crenulate anterior margins of abdominal ventrites 2 and 3.

Description. Total length 8.2–9.0 mm. Color. Dorsum black with general shagreen ( Fig. 1 ); most specimens lacking iridescent patches on elytra, with a minority of specimens possess distinct green iridescent spots laterally. Head. Ground punctation fine to moderately coarse; irregular in size ( Fig. 2 ). Systematic punctures distinct; 3–4× as large as largest surrounding ground punctures; on clypeus bearing short decumbent setae; those on frons anterior to each eye relatively long and erect. Antennae with club subequal in length to antennomeres 2–6 combined. Maxillary palpi short, apical palpomere ca. 1.6× length of penultimate palpomere; penultimate palpomere distinctly shorter than segment 2. Mentum with anterior margin slightly convex; anterior half with fine transverse microsculpture; entire mentum with fine to moderately coarse, irregularly scattered punctures. Anterior margin of head very wide, quadrate in shape. Thorax. Ground punctation on pronotum and elytra extremely fine, not detectable in some specimens. Pronotal and elytral systematic punctures large and distinct; bearing short setae. Ten rows of fine serial punctures are present in most specimens examined, which appear distinctly larger than ground punctation but less than half the size of the systematic punctures. Prosternum ( Fig. 7 ) slightly tectiform with a sharp, narrow and glabrous median carina; not distinctly elevated or dilated at anterior margin. Mesoventrite ( Fig. 6 ) elevated medially into a distinct narrow carina; surface of carina narrowly glabrous. Carina slightly depressed, appearing almost concave in lateral view. Metasternum with large elevated glabrous region that is slightly less than half as wide as long. Metafemora with moderately impressed microsculpture over most of ventral surface; proximally in the form of tiny punctures and blending distally to form of fine transverse wavy lines. Abdomen. Posteromedial glabrous region of ventrite 1 reduced, almost appearing absent. Glabrous region of ventrite 2 semi-circular to subtriangular in shape; ca. 0.3 the width of the ventrite. Anterior margins of ventrites 1–3 not crenulate, but with a loosely wrinkled appearance. Aedeagus as in Fig. 21 .

Variation. Many specimens of T. complanatus exhibit the normal shiny black and smooth dorsal appearance, which is similar to all other known species in the genus (and most members of the Oocyclus -group). However, there are a number of specimens from several collecting events in which the dorsal surface appears dull and brownish. When viewed under a microscope, the surface of these specimens is rough and coarse; the surface of “normal” specimens is smooth. I originally interpreted this difference to indicate these were two species; however, further examination of other characters, including the genitalia did not reveal any substantive differences. Even more telling, a few specimens also appear to have patches of both types of dorsal sculpture, leading me to conclude the rough-surfaced specimens represent some aberration, or are possibly caused by physical and/or chemical abrasion. I suspect the latter may be the cause because the entire surface appears to be effaced, such that the ground punctation is no longer visible and the systematic punctures appear shallower.

Etymology. Named for the broadly explanate lateral margins of the elytra and pronotum, which are distinctive of this species.

Distribution. Madagascar.

Remarks. This species is the most distinctive member of the genus and apparently the most frequently encountered. Tritonus complanatus has been collected in many regions of Madagascar, and accounts for more than half all the known specimens of the genus.

Figures

FIGURE 1. Tritonus complanatus paratype, dorsal and lateral habitus.

FIGURES 2 – 3. SEMs of head, dorsal and ventral views; 2) T. complanatus; 3) T. riambavy. Scale bar = 1 mm.

FIGURES 4 – 5. SEMs of elytra; 4) T. complanatus; 5) T. riambavy. Scale bar = 1 mm.

FIGURES 6 – 8. SEMs of thoracic sterna of Tritonus species; 6) meso- and metaventrite of T. complanatus, scale bar = 1 mm; 7) prosternum of T. complanatus, 8) prosternum of T. riambavy. Scale bars = 0.5 mm.

FIGURES 9 – 10. SEMs of stridulatory apparatus in T. complanatus; 9) laterosternite 3; 10) interior of elytra showing plectrum. Scale bars = 0.5 mm.

FIGURES 13 – 14. Details of Tritonus spp.; 13) T. complanatus, metafemora, scale bar = 1 mm; 14) T. riambavy, maxillary palpus, scale bar = 0.20 mm.

FIGURES 15 – 21. Aedeagus of Tritonus spp., dorsal view; 15) T. riana; 16) T. steineri; 17) T. riambavy; 18) T. cribratus; 19) T. madagascarensis; 20) T. crenulatus; 21) T. complanatus. Scale bar = 0.45 mm.