Mecyclothorax isolatus, Liebherr, James K., 2018

Liebherr, James K., 2018, Taxonomic review of Australian Mecyclothorax Sharp (Coleoptera, Carabidae, Moriomorphini) with special emphasis on the M. lophoides (Chaudoir) species complex, Deutsche Entomologische Zeitschrift 65 (2), pp. 177-224 : 177

Mecyclothorax isolatus sp. n. Figures 3E, 11B

Diagnosis

(n = 1). The larger body size, standardized body length 6.0 mm, ferruginous body color, and broadly transverse, ovoid pronotum (Fig. 3E) serve to diagnose this species from others of subgenus Eucyclothorax , except perhaps the smaller-bodied M. curtus (Fig. 3C). However the lateral margin of the pronotum is broadly rounded behind in this species, with the margin explanate in the region of the basal pronotal seta. The metathorax is remarkably abbreviated, more so than in any other Australian species of Mecyclothorax , with the metepisternum transversely broader than its lateral length. The elytra exhibit a subcarinate ridge along the eighth interval dorsad the subapical sinuation, reminiscent of such a carinate ridge observed in M. blackburni . The carinate ridge lies dorsad a well-developed internal elytral plica, with the plica and elytral margin fitting into a corresponding invagination along the margin of the apical abdominal ventrite, thereby forming, in concert with the conjoining of the elytra at the suture, a very robust, shell-like hindbody. Finally, there is a single dorsal elytral seta on each elytron (Fig. 3E), situated near midlength as observed in species of subgenus Qecyclothorax (Fig. 5D). Setal formula +/+/+/+/+/1/+/+.

Description.

Head capsule elongate, frons with medial depression but otherwise convex mesad the deep, sinuous frontal grooves; frontal grooves deeply and obliquely continued onto clypeus toward lateral clypeal margins; labrum slightly emarginate apically; antennae filiform, antennomere 9 length 2.36 × breadth; mandibles moderately elongate, overall length 1.57 × distance from anterior condyle to lateroapical labral margin; eyes well developed and moderately convex, ocular lobe broadly projected, outer eye surface of same curvature behind as posterior portion of lobe meeting gena, ocular ratio = 1.47, ocular lobe ratio = 0.79; mentum tooth with sides obtuse, apex broadly rounded; ligular apex moderately narrowed, 2 ligular setae separated by 3 setal diameters; paraglossae thin, extended 1/2 × as far past ligular margin as distance from base to ligular margin; mentum broad, breadth/length across the lateral lobes = 3.25. Pronotum broadly ovoid, MPW/PL = 1.31, without any indication of hind angles save a slight change of curvature of the lateral margin at the hind seta; articulatory socket of lateral seta 1 setal diameter mesad deepest part of marginal depression; median base convex, unmargined medially though broadly upraised mesad laterobasal depressions; base convex anterad basal margin, slightly depressed relative to convex disc, and separated from disc by broad, smooth oblique depressions that extend to laterobasal depressions; about 8 indistinct punctures each side from midline to mesal margins of laterobasal depressions, the depressions broadly extended to explanate lateral margin, with a low upraised tubercle in the middle of each depression; median longitudinal impression fine, well indicated, crossed by transverse wrinkles on disc; anterior transverse impression broad, shallow medially, not indicated laterally; anterior callosity slightly, broadly convex, a well-defined marginal bead along front of pronotum; front angle moderately protruded, tightly rounded; prosternal process broadly depressed between procoxae; prosternum smooth and convex medially, indistinctly punctate anterolaterally with an indistinct anteapical groove consisting of broad punctures that anastomose into a groove along lateral reaches; proepisternum impunctate, however prosternal-proepisternal suture lined with about 5 indistinct punctures; proepimeron with broadly raised posterior bead, the suture with proepisternum smooth. Mesepisternum punctate at its deepest portion, about 6 deep punctures in 1-2 dorsoventral rows. Elytra with striae 1-5 composed of isolated punctures in basal half, less punctate though traceable in apical 1/3 of length, stria 6 represented by small, isolated punctures at midlength, stria 7 absent except near apex mesad subcarinate eighth interval dorsad subapical sinuation; sutural stria broadly depressed in apical half in association with convex sutural interval, the elytra conjoined apically; stria 8 a series of deep, interrupted punctures at midlength, deep and continuous mesad the posterior series of lateral elytral setae; lateral elytral setae arrayed in 7 + 6 (anterior series setae and posterior series setae), with the posterior seta of the anterior series slightly separated from the rest; subapical sinuation angulate, abruptly curved anteriorly, with well-developed internal elytral plica visible in quarter view, though obscured by the elytral margin in dorsal view. Metepisternum short, trapezoidal, maximum breadth 1.1 × lateral length, metepimeron broadly convex posteriorly; metasternal process with sides acute, apex narrow, triangular with margin very broad medially in apex of process. Abdomen with broad linear depressions on lateral reaches of visible ventrites 3-6; suture between ventrites 1 and 2 deeply sinuous laterally, ventrite 2 depressed within sinuosity; female with 2 setae each side and a median patch of 4-5 smaller setae; apical margin of the female apical ventrite with deep emargination each side bordered laterally by a vertical, sclerotized border, these emarginations and lateral wall fitting into the elytral plica above. Microsculpture absent from frons, the surface glossy, micropunctures visible across the surface; pronotal disc and base with indistinct transverse microsculpture consisting of transverse lines and elongate meshes, these visible in surface irregularities such as wrinkles and depressions; elytral disc glossy with fine transverse lines faintly visible outside areas of reflection, elytral apex with transverse sculpticells visible in irregularly depressed areas associated with striae; metasternum glossy with indistinct transverse sculpticells, their breadth 2 –3× length; abdominal ventrites glossy with swirling transverse mesh and transverse lines. Coloration of head rufous; antennomere 1 flavous, antennomeres 2-3 rufoflavous, 4-11 with brunneous cast; pronotal disc dark rufous, margins rufoflavous; elytral disc rufobrunneous, sutural interval concolorous, interval 9 and marginal depression, and apex narrowly rufoflavous; proepipleural margin rufous, rufoflavous ventrally, proepisternum rufous; elytral epipleuron broadly flavous, margin darker, brunneous, metepisternum rufoflavous; abdominal ventrites rufoflavous with dark rufous posterior margins, apical ventrite with apical half rufoflavous; femora flavous; tibiae brunneous.

Female reproductive tract (n = 1). The unique female holotype was not dissected, however the gonocoxae are exerted from the specimen allowing the following characters to be assessed: basal gonocoxite with 2 stout apicolateral setae, medioapical surface glabrous (as in Fig. 10A); apical gonocoxite extended laterally at base, basal width about 0.7 × length, 2 stout lateral ensiform setae along lateral margin of coxite and an elongate dorsal ensiform seta present; apical nematiform setae within fossa at about 0.8 × gonocoxite length. Thus the gonocoxal configuration is most like that of M. moorei (Fig. 10A), another early divergent species within subgenus Eucyclothorax (Fig. 1).

Holotype female (ANIC): Walpole N.P. /Zig Zag Rd. WA / 20-27 June 1980 / S. & J. Peck SBP 70B // berlesate / rotted log / litter and / fungi // HOLOTYPE / Mecyclothorax / isolatus / J.K. Liebherr 2018 (black-margined red label).

Etymology.

The adjectival species epithet isolatus signifies both the geographic isolation of this species that is distributed in the south coast region of Western Australia (Fig. 11B), as well as the phylogenetic isolation of this species, as it comprises the adelphotaxon to all other species of subgenus Eucyclothorax (Fig. 1)

Distribution and habitat.

This species is known only from the tingle tree ( Eucalyptus jacksoni Maiden) forest in the south coast region of Western Australia (Fig. 11B). The single individual was collected in berlesate moist enough to support growth of fungal hyphae (S. B. Peck, pers. comm.). The vestigialized flight wings occur in concert with an extremely abbreviated metathorax and a well-developed plical lock between the elytra and apical abdominal ventrite. This species’ adelphotaxic relationship to the remainder of subgenus Eucyclothorax (Fig. 1) supports its long-term term persistence in this region since the early diversification of all Mecyclothorax .