Mecyclothorax argutulus, Liebherr, James K., 2015

Liebherr, James K., 2015, The Mecyclothorax beetles (Coleoptera, Carabidae, Moriomorphini) of Haleakala-, Maui: Keystone of a hyperdiverse Hawaiian radiation, ZooKeys 544, pp. 1-407 : 159-162

Taxon classification Animalia Coleoptera Carabidae

(065) Mecyclothorax argutulus sp. n. Figs 81D, 82 C–D, 86

Diagnosis.

This species (Fig. 81D) and Mecyclothorax argutuloides (Fig. 87C) comprise a second sister-species pair within the Haleakalā Mecyclothorax argutor group. Both species can be told by the broad, robust pronotum that is little constricted basally, MPW/BPW = 1.38-1.40. Of the two, this species displays a more robust appearance, with the pronotal lateral margins broad, and elytra broadly expanded laterally with broad, translucent lateral marginal depressions. The eyes of Mecyclothorax argutulus beetles are also less convex, ocular ratio = 1.33, though covering about as much of the ocular lobe as observed in Mecyclothorax argutuloides ; ocular lobe ratio for this species = 0.69, ratios of Mecyclothorax argutuloides individuals span 0.68-0.73. Setal formula 2 2 2-4 2; the single specimen has two dorsal elytral setae on the left elytron, four on the right. Standardized body length 6.1 mm.

Description

(n = 1). Head capsule with frontal grooves broad near clypeus, a broad, straight lateral carina extended to anterior supraorbital seta; dorsal surface of neck slightly concave; ocular lobe broadly expanded from gena, outer surface of eye not extended beyond curvature of lobe; horizontal diameter of eye crosses 18-19 ommatidia; labral anterior margin broadly, shallowly emarginate; antennae filiform, antennomere 3 sparsely setose; mentum tooth with sides acute, apex pointed. Pronotum slightly transverse, MPW/PL = 1.22, the lateral margins distinctly sinuate before the acute, very projected hind angles, the pronotal base broad so that MPW/BPW = 1.40; median base depressed relative to disc, rugose due to dense wrinkles and punctures; basal margin broadly extended medially between laterobasal depressions; median longitudinal impression fine, shallow, crossed by shallow transverse wrinkles; anterior transverse impression deeply incised, smooth, anterior callosity broadly convex, smooth; front angles well projected, rounded; pronotal apical width subequal to broad basal width, APW/BPW = 0.98; lateral marginal depression broad, margin broadly upraised; laterobasal depression broad, slightly upraised tubercle present. Proepisternum with 6 punctures along hind marginal groove; prosternal process medially concave, margin smoothly upraised. Elytra subquadrate, broadest behind middle, MEW/MPW = 1.38 elytral disc flat, sides moderately sloped; basal groove recurved at tightly rounded humerus, MEW/HuW = 1.83; parascutellar seta present; parascutellar striole deep, smooth, with 5 elongate punctures; sutural interval slightly convex, similar to lateral intervals; sutural and 2nd striae of subequal depth from base to apex; discal striae 1-5 minutely punctate, continuous, stria 6 reduced, very shallow, stria 7 traceable only; 8th interval laterad 7th stria of similar convexity to more medial intervals; the 2 paired dorsal elytral setae at 0.24 –0.27× and 0.54- 0.56 × elytral length, extra dorsal setae on the right elytron at 0.45 × and 0.82 × elytral length, setal impressions shallow, spanning about ½ width of interval 3; apical and subapical setae present; lateral elytral setae arranged in anterior series of 7 setae and a posterior series of 6 setae; elytral marginal depression moderately broad, translucent and lined with sculpticells, margin upturned; subapical sinuation shallow, broad. Mesepisternum with ~6 shallow punctures on a glossy surface; metepisternal width to length ratio = 0.89; metepisternum/metepimeron suture a broad, incomplete depression; metathoracic flight wing a triangular flap, 1.7 × long as broad, remnant R and M veins present, the flap extended to hind margin of metanotum. Abdomen with shallow indistinct lateral wrinkles on ventrites 1-3; suture between ventrites 2 and 3 complete; apical male ventrite with 2 marginal setae. Legs-metatarsomere 1/metatibial length ratio = 0.17; metatarsomere 4 length along outer lobe 1.25 × medial tarsomere length, apical and subapical setae present; metatarsal dorsolateral sulci broad, shallow. Microsculpture of vertex shallow isodiametric sculpticells in transverse rows; pronotal disc with shallow transverse mesh, median base with distinct isodiametric sculpticells; elytral disc with an elongate transverse mesh, the sculpticells more distinct on the elytral apex; metasternum with distinct transverse mesh; laterobasal abdominal ventrites with swirling isodiametric and transverse microsculpture. Coloration of vertex brunneous with piceous cast; antennomeres 1-3 and base of 4 rufoflavous, apical portion with piceous cast; pronotal disc rufopiceous, lateral marginal depression broadly rufoflavous; proepipleuron rufoflavous with piceous cast, proepisternum rufopiceous; elytral disc reflective rufobrunneous with piceous cast, sutural interval concolorous basally, rufoflavous apically; elytral margins narrowly rufoflavous in lateral depression, apex slightly, broadly paler; elytral epipleuron rufoflavous, metepisternum rufopiceous; abdomen rufopiceous, slightly paler laterally, apical half of apical ventrite broadly paler, rufoflavous; metafemur and metatibia rufoflavous.

Male genitalia (n = 1). Aedeagal median lobe very robust, distance from parameral articulation to tip 3.6 × depth at midlength (Fig. 82C); apex narrowly extended beyond ostial opening, tip angled downward, tightly rounded; median lobe curved rightward near apex in ventral view (Fig. 82D), median shaft very broad, expanded medially, maximum breadth 0.37 × parameral articulation-tip distance; internal sac with very large dorsal ostial microtrichial patch (right patch in Fig. 82D), plus well-developed ventral ostial microtrichial patch; flagellar plate moderately short, length 0.33 × parameral articulation-tip distance (estimated from shadow of sclerotized plate inside dorsal margin; Fig. 82C).

Holotype.

Male (CUIC) dissected and labeled: HI:Maui Haleakala / Hanawi N.A.R. Kuhiwa / Str. E Poouli Cabin 6-V- / 1998 lot 03 1615 m el. / under rocks along / stream C.P. Ewing // HOLOTYPE / Mecyclothorax / argutulus / Liebherr / det. J.K. Liebherr 2015 (black-margined red label).

Etymology.

The adjectival species epithet argutulus is the diminutive of argutus, clear, bright, or sharp ( Brown 1956).

Distribution and habitat.

This species is known from Kuhiwa Stream, 1600 m elevation on the Hanawī windward face of Haleakalā (Fig. 86). The type specimen was collected from under a rock in the streambed; an unusual microhabitat for a Mecyclothorax beetle on Maui. However on the island of Moloka‘i where streams have smaller catchments and lower flow rates, several Mecyclothorax have been collected in streamside habitats, including Mecyclothorax argutor (Sharp), Mecyclothorax palustris (Sharp), and Mecyclothorax cymindoides Liebherr (2007).