Mecyclothorax unctus (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 : 289-291

Taxon classification Animalia Coleoptera Carabidae

(114) Mecyclothorax unctus (Blackburn) Figs 154C, 155C, 158 A–B, 159, 160

Cyclothorax unctus Blackburn 1881: 227.

Thriscothorax unctus , Sharp 1903: 257.

Mecyclothorax unctus , Britton 1948b: 138.

Diagnosis.

These beetles exhibit uniformly dark, rufobrunneous to rufopiceous body color (Fig. 158 A–B), with the dorsal surface glossy due to the very transverse microsculpture. They are broad-bodied beetles with pronotum transverse, MPW/PL = 1.22-1.33, and elytra basally broad and subquadrate, MEW/HuW = 2.05-2.19. This breadth of body distinguishes them from the Mecyclothorax palustroides triad (Figs 149B, 158 C–E). Nevertheless, this widely distributed species (Fig. 160) exhibits substantial variation in body size (standardized body length 3.7-5.2 mm), elytral breadth (Fig. 158 A–B), and elytral striation. The discal striae 1-3, 1-4, 1-5, or 1-6 may be traceable by deeply impressed striae medially and linear series of isolated punctures laterally. Setal formula 2 1(2) 2 0; the basal pronotal setae may be present in rare instances (e.g. Fig. 158B).

Identification

(n = 5). The eyes are moderately convex, ocular ratio = 1.49-1.52, covering much of the moderately protruded ocular lobes, ocular lobe ratio = 0.77-0.83. The pronotum is distinctly constricted basally, MPW/BPW = 1.57-1.63, with the lateral margins subparallel for a short distance anterad the sharply obtuse hind angle, its obtuseness based on the curved basal margin inside the angle. The depressed pronotal median base is covered with>20 isolated punctures each side, the punctures more elongate at the juncture of base and disc. The elytral apex has striae 1, 2 and 8 always present, and an apical portion of stria 7 may also be present just laterad the apex of stria 2. Microsculpture includes: 1, vertex with indistinct transverse mesh, sculpticell breadth 2 –3× length; 2, pronotal disc and median with indistinct elongate transverse mesh, sculpticell breadth 2 –4× length, to transverse lines not joined into a mesh, the base with glossy areas between areas of microsculpture; 3 elytral disc and apex with distinct, regular transverse mesh, sculpticell breadth 2 –3× length. The head and pronotal disc are rufobrunneous with a piceous cast, the elytral disc slightly darker rufopiceous with a cupreous reflection. The legs are contrastedly rufoflavous, and in some individuals the femora are covered medially with a piceous cloud.

Male genitalia (n = 24). Aedeagal median lobe variably robust, distance from parameral articulation to tip 3.0 –4.2× depth at midlength (Fig. 159D, K); apex extended 1.3 –2.0× depth beyond ostial opening (Fig. 159L, M); median lobe shaft symmetrical in ventral view, apex offset to right, with convex left margin sinuously adjoining obliquely blunt apex (Fig. 159C, G); internal sac broad, columnar, with variously developed dorsal ostial microtrichial patch (Fig. 159 D–E, H, L), or distinct ventral ostial microtrichial patch (Fig. 159 D–E); flagellar plate moderately sized, length 0.38 –0.47× parameral articulation-tip distance. There is substantial aedeagal variation across the range of this widespread species (Fig. 160). Some of this variation occurs within regions of the mountain: 1, median lobe robustness and length in the Waikamoi area (Fig. 159A, B); 2, breadth of apical extension near Kuiki (Fig. 159 I–J); 3, length of apical extension in Kīpahulu Valley (Fig. 159 K–M). The major pattern involves aedeagi with more well developed ventral ostial microtrichial patches in beetles from Waikamoi versus from localities to the east surrounding Kīpahulu Valley. Further studies of population structure within this geographically disjunct species (Fig. 160) are warranted.

Female reproductive tract (n = 1). Bursa copulatrix columnar, parallel sided, length 0.91 mm, breadth 0.34 mm (Fig. 154C); bursal walls translucent, thinly wrinkled; gonocoxite 1 with 3-4 apical fringe setae, 10-11 small setae on medial surface from medioapical angle to base (Fig. 155C); gonocoxite 2 subtriangular, apex subacuminate, base moderately extended laterally, 2 short lateral ensiform setae, apical nematiform setae on medioventral surface at 0.73 × gonocoxite length.

Lectotype.

Female (BMNH) hereby designated, labeled: mounting platen with Blackburn Maui label ( Zimmerman 1957: 210), unctus (on reverse) // Type // Hawaiian Is. Rev. T. Blackburn 1888-30 // LECTOTYPE Cyclothorax unctus Blackburn J.K. Liebherr 1998 (black-margined red label).

Distribution and habitat.

Mecyclothorax unctus exhibits a densely collected bipartite distribution, with specimens known from throughout the Waikamoi area, and disjunctly from Hanawī through the Hāna Bogs and Kīpahulu Valley, plus the Manawainui Planeze and the eastern margin of Haleakalā Crater (Fig. 160). The species exhibits a broad elevational distribution, with Kīpahulu Valley occupied from 915 m elevation to the valley rim at Kuiki at 2285 m elevation. Elevations of occupied habitat in Waikamoi are less disparate, ranging 1210-2060 m, perhaps due to the drier nature of the subalpine habitats along the leeward edge of the volcano. The species may be very abundant in disturbed ground-level situations, such as feral pig rootings, and may occur under rocks along stream margins. It has been recorded repeatedly from microhabitats associated with ‘ōhi‘a-mossy trunks, humus and leaf litter-but never from situations associated with koa . Other plant substrates from which it has been collected include Athyrium fern ('akolea), Leptecophylla (pūkiawe), Rubus ( ‘ākala), and Vaccinium ('ōhelo).