Trientoma jilae, Steiner, Warren E. & Jr, 2006

Steiner, Warren E. & Jr, 2006, New species of darkling beetles (Coleoptera: Tenebrionidae) from San Salvador Island, Bahamas, Zootaxa 1158, pp. 1-38 : 3-8

Trientoma jilae , new species

( Figs. 1 A–B, 2A, 3A–B, 3E)

Description

Holotype, MALE: Body length 9.1 mm; greatest width 4.2 mm (at about basal 1/5th of elytra); robust, elongate­oval in outline ( Fig. 1 A–B, 3E), with pronoto­humeral margin nearly continuous; color black dorsally, very dark brown ventrally, with appendages dark brown; surfaces variably shining to alutaceous, with very minute, fine golden setae.

Head ( Fig. 2 A) with fused frons, clypeus evenly convex; surface with small punctures, transverse, arcuate rugae across fronto­clypeal region, becoming heavily rugose­carinate, polished laterally; punctures separated by one to two times the diameter of a puncture; rugose area covering much of frons (except for median triangular area) from lateral clypeal invaginations to vertex, posterad of eye; lateral­most carina above eye wider, more elevated than others; epistomal surface smooth, less rugose, with small scattered punctures. Clypeus with truncate apex; margin very slightly produced medially, expanded laterally. Antennae 2.6 mm long; second antennomere (pedicellus) only ½ as long as third antennomere; antennomere 10 widest; smaller apical antennomere paler brown.

Prothorax transverse, as wide as elytra at humeri, widest at posterior corners; sides feebly curved and gradually converging from base to narrowly rounded anterior corners; posterior and anterior margins smoothly sinuate from sides to middle, edges narrowly polished; posterior corners slightly produced posteriorly. Pronotum with lateral margins strongly beaded; pronotal surface evenly convex across disc, very slightly explanate at posterolateral corners, alutaceous, with fine punctures medially, punctures becoming larger and elongate laterally, coalescing, forming rugulose lateral thirds of disk which are feebly shining. Ventral surfaces of prothorax coarsely punctate, episternum longitudinally punctate­rugose; punctures of prosternum separated usually by less than their diameters; prosternal process with a median furrow between procoxae, raised, polished at sides, deflexed before prominent, horizontal apex in lateral view; surface polished, punctures few. Mesosternum punctate as on prosternum but median punctures larger, more separated, and surfaces more shining; mesepimeron mostly impunctate, with a few small punctures anteriorly; metasternite with punctures more widely spaced than on prosternum, of varying size, from very fine medially to large and deep laterally, where confined to anterior half.

Legs with surfaces more shining than ventral sclerites, finely punctate, sparsely setose. Front tibia widened from base to broad, truncate apex; margins feebly arcuate; dorsolateral edge nearly straight, with a row of stout tooth­like setae. Tarsi unmodified; hind tarsi about 2/3rds as long as hind tibiae; basal tarsomere nearly as long as remaining three combined.

Elytra with sides evenly arcuate from humeri to apices; middle of dorsum nearly flat; striae feebly defined with inconspicuous, widely spaced, small, shallow punctures with polished centers; lateral stria along epipleural bead with a series of larger punctures along mid­length; dorsal surface smooth, distinctly alutaceous, with extremely small, fine golden setae. Epipleurae smooth; width narrowing gradually from humerus to elytral apex, concave near humerus, flat along mid­length, becoming grooved toward elytral apex.

Abdomen with all sternites smooth, evenly convex across middle, minutely punctate, feebly alutaceous. Tegmen 1.6 mm long; widest at hinge of basal and apical piece ( Fig. 3 A), nearly as wide, sub­parallel along middle 3/5ths; apical piece narrowing from midlength to apices of parameres, with sides straight, converging, then abruptly narrowing to narrowly rounded apices, these touching at cleft, forming a small emargination; in lateral view ( Fig. 3 B) arched dorsally, with apical and basal piece with feeble dorsal emargination at junction; apex of parameres simple, slender and narrowly rounded. Ratio of length of apical piece to basal piece 15:13.

FEMALE. Similar to male except abdominal sternites 1, 2 slightly more convex medially.

Material examined

“ BAHAMA ISLANDS: San Salvador, Sandy Point, 23°58’N, 74°33’W, 17 February 2004 / W. E. Steiner & J. M. Swearingen collectors” (holotype and 13 paratypes); same data except “ 19 February 2004 ” (2 paratypes); same data except “Sandy Hook, 23°58’N, 74°28’W, 20 February 2004 (1 paratype).

Diagnosis

The larger body size, surface features, and form of the aedeagus will serve to identify this species. The size range does not overlap with that of its smaller congener described below. It appears to be closely related to Trientoma wickami Casey (1907) , the only other Trientoma described from the Bahamas (“Egg Island ”) but the holotype has a nearly smooth vertex, not rugose, the pronotum is finely punctate, not rugose laterally, and the strial punctures are more distinct. Other related but undescribed species in this group are known from other Bahamian islands, including the Turks and Caicos.

Etymology

The specific name “ jilae ” is derived from the name “Jil” + the Latin genitive possessive feminine ending “­ae” to honor my wife, Jil Marie Swearingen, who discovered the first specimen of this distinctive beetle and has helped in countless ways in Bahamian fieldwork, including photography of the habitats and collection sites.

Distribution

Trientoma jilae is known only from San Salvador Island and is presumably endemic. The only two sites where it was found are on the southern points of the island, and in a small forested area at Sandy Point was it discovered in numbers.

Habitats and collection notes

All specimens were collected on deep, coarse, coral sand under leaf litter, palm thatch and wood debris on high sandy ground behind the beach strand, in sites partly shaded by shrub and tree canopy, e.g. Bursera simaruba , Coccothrinax argentata , Coccoloba uvifera . Trientoma jilae was found to be locally abundant on the forested upper area behind the beach and at the foot of a steep hill at Sandy Point, the type­locality. Specimens were found co­occurring with the Branchus and larger Diastolinus species described in this paper, in dry sites at edges of light gaps but under larger accumulations of palm thatch and leaf litter. Two associated larvae, most likely belonging to this species, were found just beneath the surface in the loose sand beneath the litter layer.

Figures

FIGURE 1. Two Trientoma species, holotypes. A, T. jilae, new species, dorsal view; body length 9.3 mm. B, same, ventral view. C, T. voegeliorum, new species, dorsal view; body length 6.2 mm. D, same, ventral view.

FIGURE 2. Two Trientoma species, holotypes, oblique frontal views of heads, imaged to scale with each other. A, T. jilae, new species; head width at eyes 2.3 mm. B, T. voegeliorum, new species, head width at eyes 1.6 mm.

FIGURE 3. Two Trientoma species, holotypes, imaged to scale with each other. A­B, T. jilae, new species, male genitalia, dorsal and lateral views, respectively; length of tegmen 1.6 mm. C­D, T. voegeliorum, new species, male genitalia, dorsal and lateral views, respectively; length of tegmen 1.3 mm. E­F, dorsal views of T. jilae (body length 9.3 mm) and T. voegeliorum (body length 6.2 mm), respectively.