Mecyclothorax robustus (Blackburn)

Liebherr, James K., 2015, The Mecyclothorax beetles (Coleoptera, Carabidae, Moriomorphini) of Haleakala-, Maui: Keystone of a hyperdiverse Hawaiian radiation, ZooKeys 544, pp. 1-407 : 70-72

Taxon classification Animalia Coleoptera Carabidae

(025) Mecyclothorax robustus (Blackburn) Figs 37D, 38 C–D, 39B, 41, 42

Cyclothorax robustus Blackburn 1881: 228; Blackburn and Sharp 1885: 215.

Thriscothorax robustus , Sharp 1903: 268; Swezey 1954: 7 ( koa associate).

Mecyclothorax robustus , Britton 1948b: 166.

Mecyclothorax robustus Sharp 1903: 255.

Mecyclothorax robustus , Britton 1948b: 166 (synonymy).

Diagnosis.

This and Mecyclothorax haydeni represent the two larger bodied species in this group with subquadrate elytra, the discal elytral striae lined with distinct, round punctures (Figs 38 C–E). Of the two species, the discal elytral striae are more distinctly and regularly punctate in Mecyclothorax robustus , though this characteristic is variable. In aggregate, individuals of Mecyclothorax robustus have larger eyes, ocular ratio = 1.48-1.54, that cover most of the ocular lobe, ocular lobe ratio = 0.76-0.84, in contrast to beetles of Mecyclothorax haydeni with ocular ratio = 1.41-1.49, and ocular lobe ratio = 0.70-0.78. Male genitalia are diagnostic, with the aedeagal median lobe of Mecyclothorax robustus males exhibiting an apex with a flattened apical surface and tightly rounded, ventrally directed tip (Fig. 41), versus a median lobe with an evenly downcurved and narrowed apex for Mecyclothorax haydeni (Fig. 43). Setal formula 2 2 2 2. Standardized body length 4.8-6.1 mm.

Identification

(n = 5). In keeping with the larger eyes, the posterior portion of the ocular lobe joins the gena at nearly a right angle in this species, with a shallow groove at the juncture of lobe and gena. The pronotal median base is covered with distinct punctures, and longitudinal wrinkles line the juncture with the disc; the anterior transverse impression is deep, narrow, and crossed by deep wrinkles, its posterior surface lined with isodiametric microsculpture. The pronotum is variably transverse, MPW/PL = 1.20-1.28, with variably moderate basal constriction, MPW/BPW = 1.34-1.50. The parascutellar striole is distinctly 5-punctate, and striae 1-6 are distinctly punctate basally, and slightly irregular to smooth apically. The elytral disc is rufobrunneous, often with a purplish reflection due to the transverse-mesh to transverse-line microsculpture covering the intervals.

Male genitalia (n = 36). Aedeagal median lobe gracile, distance from parameral articulation to tip varies 3.5 –4.8× depth at midlength (Fig. 41B, F); apex moderately extended beyond ostial opening, but always with apical face flat and tip rounded at juncture of apical face and ventral margin; median lobe slightly curved rightward in ventral view, the curvature of left margin more exaggerated in more robust aedeagi (e.g., Fig. 41C versus 41H, which is same specimen as 41F); internal sac parallel sided, dorsal and ventral microtrichial patches variably developed (Fig. 41B, E, G); flagellar plate moderately large, length of sclerotized ventral face 0.44 –0.48× parameral articulation-tip distance.

Female reproductive tract (n = 2). Bursa copulatrix columnar with expanded apex, length 1.25-1.28 mm, breadth 0.48-0.51 mm, basal breadth 0.34 mm in one specimen (Fig. 39B), basal breadth subequal to apical breadth in second specimen; bursal walls translucent with thick wrinkles; gonocoxite 1 with 2-3 apical fringe setae and 7-10 smaller setae on medial surface (Fig. 37D); gonocoxite 2 narrowly subtriangular with subacuminate apex, base narrowly extended laterally, 2 lateral ensiform setae with apical seta broader and longer, apical nematiform setae on medioventral surface at 0.74 × gonocoxite length.

Types.

For Cyclothorax robustus Blackburn, holotype female (BMNH) labeled: mounting platen with Blackburn Maui code ( Zimmerman 1957: 210), Cyc robustus (on reverse) // Type // Rev. T. Blackburn 1888-30. // HOLOTYPE Cyclothorax robustus Blackburn J.K. Liebherr 1998 (black-margined red label). For Mecyclothorax robustus Sharp, lectotype male (BMNH) labeled: Mecyclothorax robustus D.S. Type Haleakala Perkins 622 // Type // Hawaiian Is. Perkins 1904-336 // LECTOTYPE Mecyclothorax robustus Sharp J.K. Liebherr 1998 (black-margined red label).

Distribution and habitat.

The distributions of Mecyclothorax robustus and Mecyclothorax haydeni subdivide the windward face of Haleakalā, with this species found from Kuhiwa Valley on the east to the leeward forest edge near Makawao on the west (Fig. 42) at elevations spanning 1137-1830 m. Historical Perkins records can be predominantly assigned to Ukulele Camp ( Perkins 1894, 1896a, b). The species is distributed in ‘Ōhi‘a and Koa Forest formations, though most direct associations involve beetles being found in moss on ‘ōhi‘a, and secondarily on hāpu‘u ( Cibotium ) or on ‘ōhi‘a nurse logs. This is an abundant species within its habitats. Beetles can be beaten from vegetation at night, or found under boards or logs either during day or at night.