Mecyclothorax gracilicollis, 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 : 199-201

Taxon classification Animalia Coleoptera Carabidae

(083) Mecyclothorax gracilicollis sp. n. Figs 100D, 101

Diagnosis.

This is by far the smallest-bodied Haleakalā species in the Mecyclothorax scaritoides group; standardized body length 3.8 mm. The pronotum is basally constricted (Fig. 100D), MEW/BPW = 1.59, and the elytra are ellipsoid. These body proportions and size are similar to those of the O‘ahu Mecyclothorax scaritoides group species, Mecyclothorax simiolus (Blackburn) and Mecyclothorax pelops Liebherr ( Liebherr 2009a). However, beetles of the O‘ahu species lack pronotal setae, thereby fitting setal formula 2 0 2 0, and Mecyclothorax gracilicollis is characterized by a bisetose pronotum and therefore this species matches the 2 1 2 0 setal formula of the other Haleakalā species in the group.

Description

(n = 1). Head capsule with frontal grooves broad near clypeus, only slightly sinuous, a broad convexity laterad groove before eye, and low carina mesad anterior supraorbital seta; dorsal impression impression of neck slightly concave concave; eyes little convex, ocular ratio = 1.39, but covering much of ocular lobe, ocular lobe ratio = 0.80; labral anterior margin angularly emarginate 1/6 labral length; antennae filiform, antennomere 2 with 1 short seta on shaft, antennomere 3 with 2 such setae; mentum tooth with sides acute, apex tightly rounded. Pronotum little transverse, MPW/PL = 1.19; hind angle sharp, obtuse due to curved basal margin inside hind angle, the lateral margin subparallel anterad angle; median base slightly depressed, ~18 small punctures each side; basal margin moderately convex between hind angles; median longitudinal impression shallow, narrowly defined, crossed by indistinct transverse wrinkles; anterior transverse impression very shallow, broad, obsolete medially, smooth; anterior callosity slightly convex, smooth, glossy; front angles slightly projected, tightly rounded; pronotal anterior width greater than basal width, APW/BPW = 1.05; lateral marginal depression narrow, edge upturned throughout length except beaded at front angle where depression is slightly broader; laterobasal depression with irregular surface continued from median base. Proepisternum with 5 minute punctures along hind marginal groove; prosternal process narrowly, evenly depressed medially. Elytra with disc slightly convex medially, side distinctly sloped to margin; basal groove curved to subangulate humerus, humeral angle defined by hitch in depression caused by juncture of narrow basal groove and broader marginal depression, MEW/HuW = 2. 17; parascutellar seta present; parascutellar striole with 4-5 punctures, deep, continuous between punctures; sutural interval more convex than slightly convex interval 2, sutural juncture upraised; sutural stria shallow, broad, minutely punctate basally, finely incised, deep, and smooth apically; striae 2-3 very shallow, striae 4-6 traceable and stria 7 obsolete on disc, apically striae 2-4 and 7 very shallow, incomplete, striae 5-6 obsolete; elytral intervals 2-3 slightly convex on disc, intervals 4-5 flat; 8th interval laterad 7th stria slightly more convex than fused apical portion of striae 5 + 7; 2 dorsal elytral setae at 0.29 × and 0.56 × elytral length, setal impressions very small, spanning ½ width of interval 3; lateral elytral setae arranged in anterior series of 7 setae and posterior series of 4-5 setae; elytral marginal depression broader laterad humerus to midlength, beadlike near subapical sinuation; subapical sinuation evident, more abruptly incurved anteriorly. Mesepisternum with ~10 punctures in 2-3 rows; metepisternal width to length ratio = 0.87; metepisternum/metepimeron suture distinct. Abdomen with irregular lateral wrinkles in ventrites 1-3, circular lateral depressions in ventrites 3-6; suture between ventrites 2 and 3 partially effaced; apical female ventrite with 4 equally spaced setae plus median trapezoid of 4 subequal, short setae. Legs-metatarsomere 1/metatibial length ratio = 0.19; metatarsomere 4 length along outer lobe 1.3 × medial tarsomere length, apical and subapical setae present; metatarsal dorsolateral sulci shallow, broad, median area broad. Microsculpture of vertex very shallow, transverse, sculpticell breadth 2 –3× length; pronotal disc with obsolete transverse lines in part, glossy between sculpticells, median base glossy, indistinct transverse cells laterally; elytral disc with regular, distinct transverse mesh, sculpticell breadth 2 –4× length, apex with shallow transverse mesh, sculpticell breadth 2 –4× length; metasternum with shallow transverse mesh, sculpticell breadth 3 –4× length; laterobasal abdominal ventrites with swirling isodiametric and transverse microsculpture. Coloration of vertex rufobrunneous; antennomeres 1-3 rufoflavous, 4-11 rufobrunneous; pronotal disc rufobrunneous, lateral margins, base, and apex narrowly rufoflavous; proepipleuron rufoflavous, proepisternum rufobrunneous; elytral disc rufobrunneous with iridescent sheen, sutural interval rufoflavous basally and apically, rufous on disc; elytral lateral marginal depression narrowly rufoflavous, apex rufoflavous apicad subapical sinuation; elytral epipleuron rufoflavous, metepisternum rufobrunneous; abdominal ventrites 1-6 rufobrunneous, ventrites 2-3 slightly paler laterally, apical 1/3 of apical ventrite flavous; metafemur rufoflavous; metatibia rufobrunneous.

Female reproductive tract. The lone female specimen was not dissected.

Holotype.

Female (CUIC) labeled: HI: Maui Haleakala N.P. / Kipahulu west rim below / Kuiki sift humus ex ohia / 14-V-1993 lot 04 / el. 2090 m // J.K. Liebherr & / A.C. Medeiros / Collectors // HOLOTYPE / Mecyclothorax / gracilicollis / Liebherr / det. J.K. Liebherr 2015 (black-margined red label).

Etymology.

This species epithet combines the Latin adjective gracilis, slender or thin, with the Latin noun collis, or hill. The noun gracilicollis is used here to signify the basally constricted pronotum of beetles of this species.

Distribution and habitat.

The type specimen of Mecyclothorax gracilicollis was collected on the western rim of Kīpahulu Valley, 2090 m elevation (Fig. 101), in sifted humus from ‘ōhi‘a. Other Mecyclothorax species represented in the sample containing the type specimen are: Mecyclothorax antaeus , Mecyclothorax consanguineus , Mecyclothorax iteratus , Mecyclothorax kuiki , and Mecyclothorax splendidus .