Hexanchorus bifurcatus, Maier, Crystal A. & Short, Andrew Edward Z., 2014

Maier, Crystal A. & Short, Andrew Edward Z., 2014, Hexanchorus bifurcatus sp. nov., a new tepui riffle beetle (Coleoptera: Elmidae: Larainae) from Tafelberg, Suriname, Zootaxa 3895 (1), pp. 137-143 : 138-141

Hexanchorus bifurcatus n. sp.

( Figs. 1–8 )

Type material. Holotype male: “ SURINAME: Sipaliwini District/ N3° 55.600', W6° 11.300'; 600m / CSNR: Tafelberg Summit/ Augustus Creek, riffles & flat/ rocks in creek in high flow areas/ leg. Short & Bloom/ 14.viii.2013; SR13-0814-01A” ( NZCS). Paratypes (39): Same data as holotype (34 exs.; NZCS, SEMC, USNM). “ SURINAME:Sipaliwini/ CSNR Tafelberg Summit, Geijskes Creek/ 3° 56' 21.0582"N, -56° 10' 57.8382"W; 614 m / 16.viii.2013 /D. Bloom colr; leaf packs scrubbing rocks; SR13-0816-01D” (3 exs.; SEMC). “ SURINAME: Sipaliwini District/ N3° 53.942', W56° 10.849'; 733m / CSNR: Tafelberg Summit nr/ Caiman Creek Camp; Caiman / Creek; leg. Short & Bloom/ 19.viii.2013; SR13-0819-04A” (2 exs.; SEMC).

Diagnosis. This species is most similar to Hexanchorus homaeotarsoides Maier, 2013 and Hexanchorus angeli Laššová et al., 2014 , but can be readily distinguished from the preceeding species by the bifurcate apices of the elytra on females of the species ( Fig. 7 ). The male genitalia are nearly identical to those of H. angeli , with only subtle differences in proportion (1.4 mm) ( Fig. 5 ).

Description. Holotype Male. Body elongate, subparallel, dorsum moderately convex. Length 3.7 mm; greatest width 1.4 mm. Body dark brown dorsally; venter medium brown to dark brownish black ( Figs 2, 3 ). Base of antenna testaceous ventrally, base of femur, trochanter testaceous ( Fig. 3 ). Dorsal surface densely covered with short recumbent setae; ventral surface densely covered with longer, golden, recumbent setae. Setae with greenish iridescence ( Fig. 2 ). Surface microreticulate, with dense fine punctures; fine punctures separated by distance equal to puncture diameter.

Head moderately coarsely, densely punctate; punctures separated by their diameter; cuticle microreticulate. Clypeus with anterior margin straight; angle on each side square; lateral angles of clypeus lacking tuft of golden setae. Labrum with anterior margin entire and broadly rounded; labrum expanded laterally, covered with setae approximately three times as long as setae on head; lateral margins of clypeus with sparse brush of golden setae. Eyes hemispherical, narrowed posteriorly and bordered by long black curved setae (“eyelashes”) that arise near dorsal and ventral sides of eyes and extend toward middle of eye. Antenna pubescent, clubbed; antennomeres 1 and 2 testaceous ventrally, with dense recumbent setae and long, dark brown setae ( Fig. 3 ). Antennae serrate, thickening slightly towards apex ( Fig. 3 ). Antennae medium-length, just reaching transverse groove of pronotum. Apical antennomeres dark brownish to black, with dense recumbent setae. Apical antennomere acuminate.

Pronotum 1.1 mm long, 1.2 mm wide, with weak median longitudinal depression and slight postero-medial impression, lacking sublateral groove; lateral margins strongly sinuate; anterolateral angles rounded, not explanate; base of pronotum slightly sinuate and with broad lobe medially; posterolateral angles acute, not explanate, declivous, depressed adjacent to each angle; disc with fine, dense punctures, separated by a distance equal to or less than their diameter; cuticle microreticulate, covered with short, dense, iridescent setae ( Fig. 2 ). Lateral projection of hypomeron absent. Prosternum short in front of procoxae; lacking tuft of setae apicomedially ( Fig. 3 ). Prosternal process parallel-sided, slightly tapering to broadly acuminate apex; disc slightly impressed, without v-shaped groove; lateral margins reflexed; middle concave ( Fig. 3 ). Scutellum broader than long, slightly convex, level with adjacent elytral intervals. Mesoventrite short, depressed, with a deep, broad, v-shaped depression for reception of apex of prosternal process. Metaventrite with disc strongly inflated on posterior three-fourths, finely punctate behind mesocoxae, punctures becoming more sparse laterally, with large, rounded depressions scattered on disc; with deep longitudinal groove on midline of disc, groove deepest and broadest on posterior third of disc; with short, dense pubescence; cuticular surface of metaventrite finely microreticulate.

Legs long and slender ( Fig. 4 ). Femora light brown proximally, becoming dark brown in distal fifth. Tibiae with dorsal surface dark brown and ventral surface light brown. Procoxae and metacoxae moderately widely separated; mesocoxae slightly more widely separated ( Fig. 3 ). Protibia lacking excavation for reception of tarsi, lacking apical tooth. Protarsus of male not expanded apicomedially. Mesotibiae of male with medial pubescent area short; lateral pubescent area only at extreme base; lacking carina on inner apex. Tarsal claws long and stout, light brown. Metafemur of male with small internal glabrous patch.

Elytron with ten rows of fine punctures; punctures separated by a distance three to four times the diameter of the puncture; intervals with short, dense, iridescent pubescence; humeral area slightly swollen ( Fig. 4 ). Elytral striae obscured apically. Elytron widening to about posterior two-thirds before converging to rounded and acute apex. Apical third of elytron not, or just barely inflated. Elytron without strong impression at basal third. Lateral bead of elytron sinuate. Elytra three times as long as pronotum; broadest point across humeri. Apex of elytron narrowly rounded; lateral margins smooth; humeri gibbous; elytral intervals slightly elevated; punctures on intervals no larger than finest punctures of head and pronotum and separated by 2–5 times puncture diameter.

Abdomen with five ventrites. First three ventrites broadly, deeply depressed and lacking carinae adjacent to metacoxae; cuticle densely covered with short, golden, recumbent setae. Last visible ventrite deeply and broadly emarginate. Aedeagus parallel-sided, strongly recurved at apex, parameres reaching more than halfway up length of aedeagus.

Female. Externally similar to male, except elytral apices strongly bifurcate and extended posteriorly ( Figs. 6 & 7 ). Protibiae slightly less curved than those of male. Mesotibiae without carina on inner apex. Metventral disc not as deeply and less extensively concave. Abdominal sterna 1–3 convex, not concave. Much like the Venezuelan species H. homaeotarsoides Maier, 2013 and H. angeli Laššová et al., 2014 , the female possesses a posterior median projection on the third abdominal ventrite, but can be distinguished from females of those species by the distinctive bifurcate elytral apices.

Intraspecific Variation. This species varies slightly in color, from dark brown to black, and shows minimal variation in size (3.5–3.9 mm TL).

Etymology. This species is named “ bifurcatus ” in reference to the bifurcate elytral apices of the female.

Habitat and Distribution. This species is known from the northwestern edge of Tafelberg, a sandstone table mountain in central Suriname ( Fig. 1 ). The longest series of specimens were collected from Augustus Creek, a medium-sized (~ 10 m across), low-order stream that drains the majority of the summit region. This tannin-rich blackwater creek is in a densely forested area with occasional breaks in the canopy directly above the stream channel ( Fig. 8 A). Most specimens were collected in riffles and high-flow areas by scrubbing rocks in the flow with a brush while holding a net on the downstream side ( Fig. 8 B). In this regard, H. bifurcatus has similar habitat preferences as other species of Hexanchorus from throughout Central and South America. Additional specimens were found in Caiman Creek (a small, upstream tributary of Augustus Creek) and Geijskes Creek.

Figures

FIGURE 1. Map of Northeastern South America showing collection localities of Hexanchorus bifurcatus n. sp. and H. angeli Laššová et al.

FIGURES 2 – 5. Hexanchorus bifurcatus n. sp., male: 2. Habitus, dorsal view; 3. Habitus, ventral view; 4. Habitus, lateral view; 5. Aedeagus, dorsal and lateral views (scale bar = 1.0 mm).

FIGURES 6 – 7. Hexanchorus bifurcatus n. sp., female: 6. Habitus, dorsal view; 7. Elytral apex, detail.

FIGURE 8. Habitat of Hexanchorus bifurcatus n. sp. on Tafelberg Tepui, Suriname. Riffle in Augustus Creek, including closeup of rock-scrubbing.