Mecyclothorax poro, Liebherr, James K., 2012

Liebherr, James K., 2012, New Mecyclothorax spp. (Coleoptera, Carabidae, Moriomorphini) define Mont Mauru, eastern Tahiti Nui, as a distinct area of endemism, ZooKeys 227, pp. 63-99 : 83-86

7. Mecyclothorax poro sp. n. Fig. 4D

Diagnosis.

This species shares with Mecyclothorax angulosus Perrault the distinctly constricted lateral pronotal margins anterad right, projected hind angles. Both species are also characterized by two supraorbital setae and two dorsal elytral setae, and therefore a setal formula of 2121. Both also display dense transverse-line elytral microsculpture loosely joined in a mesh, the microsculpture resulting in an aeneous reflection. The pronotal median base is more distinctly punctate in Mecyclothorax angulosus , and the cuticle between the punctures is covered with indistinct transverse microsculpture, versus the smooth areas between punctures observed in this new species (Fig. 4D). Elytral stria 6 is shallow and nearly smooth near the elytral midlength in this species, versus deeper and punctate-nearly as deep as striae 1-5-in Mecyclothorax angulosus . Also, elytral striae 2-6 are obsolete basally in this species, versus deep and continuously depressed to their juncture with the elytral basal groove in Mecyclothorax angulosus . Standardized body length in this species is 4.4 mm, larger than Mecyclothorax angulosus at 4.0 mm (n = 2; MNHN holotype male plus CUIC female).

Description.

Head capsule with broad, shallowfrontal grooves that extend medially as depressed triangles that nearly meet along midline posterad frontoclypeal suture, grooves terminated posteriorly mesad broad carina inside supraorbital seta, fine transverse wrinkles emenating from grooves onto frons; frons and vertex convex, neck not depressed; ocular lobe moderately protruded, meeting gena at> 135° angle, juncture marked by narrow, shallow groove; ocular ratio 1.45, ocular lobe ratio 0.76; labral anterior margin moderately emarginated medially to 1/7 length; antennomeres 1-3 glabrous except for apical setae, minute pore sensilla visible in translucent cuticle of shafts; antennae submoniliform, antennomere 8 length 1.67 × maximal breadth; mentum tooth with sides subparallel, apex rounded. Pronotum transversely cordate, MPW/PL = 1.25, base narrow, MPW/BPW = 1.56; lateral margins convergent for short distance anterad protruded, nearly right and glabrous hind angles; median base moderately depressed relative to disc, margin with disc lined with 7-8 elongate punctures, 10-12 more small, isolated punctures each side; basal margin distinctly convex between laterobasal depressions; median longitudinal impression shallow, very finely incised; anterior transverse impression shallow but continuous medially, smooth, deeper and more definite in outer ¾ of breadth each side; anterior callosity slightly convex, smooth; front angles not protruded, broadly rounded posteriorly; apical pronotal width equal to basal width; lateral marginal depression narrow, slightly broadened from lateral seta to front angle, narrowest posterad lateral seta; laterobasal depression a broadened continuation of lateral depression, surface irregularly punctured, bordered laterally and basally by broad upraised bead; proepisternum with 5 distinct punctures along hind margin, proepimeron with granulate groove along hind margin; prosternal process broad, margins broadly beaded, distinctly depressed medially between procoxae. Elytra ellipsoid, disc moderately convex, upraised above scutellum, sides approaching vertical at juncture with lateral depression; basal groove gently arcuate laterad scutellar striole, anteriorly curved to meet subangulate humerus; humeral angles proximate, MEW/HuW = 2.24; parascutellar seta present, situated near sutural stria; parascutellar striole 5-punctate, shallow but continuous between punctures; sutural interval of similar convexity to intervals 2-5 near base, but each side upraised at sutural juncture, narrowed and more convex, callouslike apically; striae 1-4 minutely punctate in basal ⅓ of length, punctures slightly expanding striae, striae 5-6 broader and shallower on disc, striae 1-6 absent near basal groove and humerus; sutural stria fine, deep at apex, striae 2 and 3 broader and shallower, 4-6 obsolete, difficult to trace, and stria 7 interrupted, deepest at short depressed strial remnant associated with apical elytral seta; eighth interval convex, although not carinate medially due to reduction of stria 7; two dorsal elytral setae in deep, evident impressions that span ½ width of third interval, setae positioned at 0.24 –0.27× and 0.51 –0.52× elytral length; apical elytral seta present, subapical seta absent; lateral elytral setae 7 + 6; elytral marginal depression moderately broad to subangulate humerus, margin upraised laterad humerus, depression broadest along anterior lateral setal series, narrowed with margin beaded along posterior setal series; subapical sinuation broad, shallow, internal plica visible in dorsal view. Mesepisternum with 16 punctures in 2-3 vertical rows; metepisternum slightly elongate, width to length ratio 0.78; metepisternum separated from met- epimeron by distinct suture. Abdomen with visible ventrites 1-4 irregularly wrinkled laterally, ventrites 4-6 with rounded depressions laterally; suture between visible ventrites 2 and 3 effaced laterally. Legs robust, metatarsomere 1 length 0.18 × metatibial length; metatarsomeres broad, tarsomere 4 broadly triangular, overall length 1.4 × median tarsomere length; metatarsomere 4 apical and subapical setae present; metatarsal dorsolateral sulci shallow and lateral, median surface broadly convex. Microsculpture of head indistinct, transverse mesh with sculpticell breadth 2 –3× length on glossy surface; pronotal disc with indistinct transverse mesh, sculpticell breadth 2 –4× length visible outside areas of reflected light; pronotal median base with indistinct transverse mesh, sculpticell breadth 2 × length among punctures; elytral disc covered with transverse lines irregularly joined into a loose mesh, the surface with aeneous reflection; elytral apex with transverse mesh, sculpticell breadth 2 –4× length; metasternum with transverse mesh; laterobasal abdominal ventrites covered with swirling isodiametric and transverse sculpticells. Coloration of head capsule piceous, clypeus rufous; antennomeres 1-2 rufoflavous, 3-11 rufobrunneous; pronotal disc dark rufous with piceous cast, median base, anterior callosity and edges of disc rufous, lateral marginal bead piceous; proepipleuron rufoflavous, proepisternum dark rufous; elytral disc dark rufous; sutural interval rufous basally, rufoflavous apically; elytral marginal depression rufous basally, rufoflavous apically; elytral apex beyond subapical sinuation rufoflavous; elytral epipleuron rufoflavous dorsally, rufobrunneous ventrally, metepisternum rufobrunneous; visible abdominal ventrites 1-6 rufobrunneous laterally, with piceous cloud medially; apical abdominal ventrite graded to flavous margin in apical third; metafemur flavous; metatibia flavous with brunneous cast.

Female reproductive tract. The unique female holotype was not dissected, nor were its external genitalia visible for examination.

Holotype. French Polynesia: Tahiti Nui / Mt. Mauru lava tube / el. 705 m 18-IX-2006 lot 01 / 17°38.017'S, 149°21.284'W / pyr. fog moss/liverworts / along stream J.K. Liebherr // HOLOTYPE / Mecyclothorax / poro / J.K. Liebherr 2012 (black-bordered red label).

Larva. One larval specimen was collected 18-ix-2006 by use of pyrethrin fog on a moss-covered boulder at the upper mouth of the lava tube, 725 m elevation. Complete description of the larva will be presented subsequently, but identification as Mecylothorax sp. is possible based on its intrinsic characters assessed within the context of the disharmonic carabid fauna of Tahiti.Using Emden (1942), the specimen keys to couplets 28 and 29 whereupon it violates the key, exhibiting various attributes agreeing with each couplet half. In accordance with couplet 28, Patrobini , the larva exhibits: 1, maxillary palpomere 2 longer and stouter than palpomere 3; 2, inner lobe, or lacinia of maxilla absent. In accord with couplet 29, Pterostichini , Drimostomina etc., it exhibits: 1, mandible with unisetose penicillus; 2, antennomere 2 shorter than 1 or 3; 3, nasale broadly and indistinctly produced.

The larval labium includes a bisetose ligula, with the setae LA1, LA2, LA3, LA4, and the ligular setal pair LA6 present, and the setae at position LA5 absent ( Bousquet and Larochelle 1984). The second pair of ligular setae-termed LA7 by Arndt (1998) -that are observed in Patrobini are not present. Also absent are the paired ligular pores homologized by Arndt with LA7. The configuration of bisetose ligula with pores substituting for LA7 is a synapomorphy for the subfamily Harpalinae (Arndt, 1998). Thus the larval ligula deviates from Patrobini by the absence of LA7, but also deviates from members of subfamily Harpalinae by absence of two pores accompanying the LA6 setae on the ligula. In sum, the larva appears to represent a grade of development between Patobini and Harpalinae . The only candidates present in Tahiti that represent that phylogenetic level would be in the genus Mecyclothorax of the Moriomorphini . Corroborating this hypothesis, the larva shares characters with that of Melisodera picipennis Westwood, an Australian moriomorphine ( Moore 1964). These characters include, among others: 1, a medially emarginated nasale; 2, cervical keel; 3, mandibular penicillus; 4, absence of a maxillary inner lobe; 5, bisetose ligula; 6, legs with two claws; and 7, urogomphi with short setose nodes.

The larva exhibits a 0.9 mm head width measured across the head capsule behind the stemmata, and a body length of 5.1 mm measured from the anterior margin of the nasale to the urogomphal tips (measurements made on a cleared larva). Based on these dimensions and the adult body length of 4.4 mm, the larva is considered to represent the third instar.

Given that Mecyclothorax poro was the only other Mecyclothorax species collected at this site, the larva is tentatively identified as that species based on geographic association. Of course, larval and adult individuals could have been deposited at this site during high water, but Mecyclothorax poro was not found at any other site suggesting this is its native habitat. Moreover, larvae and one adult of Metacolpodes eremita (Fairmaire) ( Carabidae : Platynini ) were also found together on moss-covered boulders at the lower entrance to the lava tube (Fig. 2A), suggesting that a resident streamside carabid community resides and breeds at this site.

Etymology.

Among several meanings, the Tahitian word poro means corner or angle ( Wahlroos 2002), and its use for the species epithet signifies the acute, projected hind pronotal angles characterizing this species. As Tahitian, the epithet is to be used as a noun in apposition.

Distribution and habitat.

The adult and presumed larva of this species were collected at 705-725 m elevation, from moss and liverwort covered rocks along a stream running through a lava tube “tunnel”; the uncollapsed portion of a very large lava tube (Fig. 2A). This is the lowest elevation record for any Mecyclothorax species in Tahiti. For both the adult and larva, individuals were discovered through use of pyrethrin fog on the moss and liverworts, demonstrating that the individuals inhabited the depths of that vegetation. The rock face inhabited by the adult was wet, as the mouth of the lava tube was in shade for much of the day, and the site of adult collection was within a meter of the water’s edge. The larva was found on a boulder in the middle of the streambed at the upper end of the lava tube where the moss was quite dry to the touch.