Mecodema validum Broun, 1923

Seldon, David S. & Buckley, Thomas R., 2019, The genus Mecodema Blanchard 1853 (Coleoptera: Carabidae: Broscini) from the North Island, New Zealand, Zootaxa 4598 (1), pp. 1-148 : 131-133

Mecodema validum Broun, 1923 .

Figure 63 .

Diagnosis: Geographically widespread with external variation among populations across the range, but the shape of the apical portion of the penis lobe remains almost identical throughout (slight variation in northern Hawke’s Bay population). Distinguishable from other North Island Mecodema species by having: 1, mandibles that appear narrower and longer; 2, a broad and shallow vertexal groove formed by numerous punctures; 3, punctures and short rugose wrinkles between pronotal foveae; 4, elytral interval 7 strongly convex forming a high ridge laterally on elytra; 5, apical portion of the penis lobe distinct ( Fig. 63 PL).

Description: Length 26–34.4 mm, pronotal width 7.3–9.4 mm, elytral width 8–10.6 mm. Colour of entire body matte to glossy black, coxae and legs are either black, dark red or reddish-brown.

Head: Broad and flat ( Fig. 14A ). Vertex smooth (may be wrinkles present laterally, proximate the vertexal groove); vertexal groove ( Fig. 9 ) broad and shallow, defined by punctures entire length, increasingly numerous laterally ( Fig. 63 ); small supraorbital puncture bearing 3–5 setae; 2–3 (some specimens with a greater number) well-defined supraorbital grooves, may be present anterior to supraorbital puncture; frons medially convex with a large and shallow depression each side of midline, may have grooves laterally; frontoclypeal suture very fine, tentorial pits indistinct; anterior area of clypeus with grooves (may be indistinct), 1 large setose puncture on each side bearing 2 setae ( Fig. 63 ) (some specimens with 1 large setose puncture medially bearing 2 setae). Labrum lobate, anterior edge moderately emarginated with 2 proximate central setae, 2 setae each side evenly spaced. Mentum lobes rounded ( Fig. 12F ), median process short and broad, moderately angled upward (30°), moderately indentate ( Fig. 12B ), mentum setae absent. Submentum sclerite constriction narrow (curved anteriorly medially) with 6 evenly spaced setae. Stipes with 2 basal setae. Gula pits very small, suture poorly defined, gula flat with very fine transverse lines. Gena ( Fig. 8 ) with well-defined wrinkles forming an isodiametric pattern across entire area.

Prothorax: Prothoracic carina broad the entire length, crenulations absent with 7–11 setae each side, extended to anterior angle; posterior lateral sinuation evidently carinate, slightly angled outward; pronotum broad and flat, overall shape cordate ( Fig. 63 ); midline indistinct, anterior medial and posterior medial diamond-shaped impressions present, disc with lightly impressed transverse wrinkles laterally ( Fig. 63 ); pronotal foveae deep and very broad (creates distinctive curve mesad of foveae), rugose wrinkles on base of pronotum extended from foveae to midline, some specimens with sparsely interdispersed punctures; anterior edge inwardly curved, posterior edge curved laterally, usually emarginated medially ( Fig. 63 ). Prosternum flat with slightly impressed transverse striations that are evenly spaced (some specimens with obsolescent punctures laterally); proepisternum with numerous obsolescent punctures. Procoxal setae absent; protibia distally expanded and shovel-like ( Fig. 10B ).

Elytra: Broad and flat, slightly deflected laterally (appears narrow), steeply sloped to apex; humeral angle evenly convex ( Fig. 6B ); basal margin slightly curved and gently sloped to base, interval 1 extended to scutellum; lateral carina narrow the entire length, extended to humeral angle; humerus with 4–5 setose punctures: 4 proximate the angle, 1 double-spaced posterad ( Fig. 63 ); suture lightly impressed; striae with small, regularly distributed, asetose punctures; intervals 1–5 flat, intervals 6 and 8 weakly convex, interval 7 strongly convex, especially anterior ⅓; interval microsculpture present as very fine transverse lines; 7 th strial setal pattern with 3–4 setose punctures in anterior ½, 4–6 setose punctures in posterior ½, setose punctures large.

Ventral surface: Mesepisternum with distinctly impressed punctures across entire area (some specimens with rugose wrinkles with punctures interdispersed within wrinkles), metepisternum without microsculpture; setose punctures present on mesocoxae (1) and metacoxae (3). All abdominal ventrites ( Fig. 2 ) lineate laterally (some distinctly impressed), ventrites 1 and 2 with obsolescent punctures; ventrites 3–5 with 1 setose puncture each side of midline; ventrite 6 setae present: ♂ with 1–2 setose punctures each side at junction of straight apical edge and curve anterad, ♀ with 2–3 setose punctures each side along rounded apical edge; ventrites foveate (very shallow) laterally. Anterior metaventrite process ( Fig. 2 ) long, narrowly triangular with a very broad and well-defined carina the entire length.

Male genitalia: Apical portion of penis lobe asymmetrically hooked with a moderate deflection to right of vertical axis ( Fig. 15B ), dorsal process distinctly recurved over shaft ( Fig. 63 PL) (Boundary Stream Mainland Island population with dorsal process moderately recurved) with brief and sharp curve to shaft, ventral process a sharp point (Ruahine Ranges population) to the more general rounded point; shaft of penis lobe narrow with a strong curve to right in Te Aroha population (especially in apical ⅓), shaft of penis lobe with moderate curve to right in Pureora Forest population (over entire shaft) (VV); overall length of penis lobe moderately curved ventrally ( Fig. 16B ) (LV). Structures of the endophallus ( Fig. 4 ): lateral form of the apex of the central spicule pointed; dorsal form of the apex of the central spicule greatly expanded with projection; setal (scales) coverage of the apical plate extensive (76–100%); size of left setose flange small; size of right setose flange absent. Left paramere articulated at right angle to penis lobe, basal lobe triangular due to large dorsal hump (e.g., Mt Te Aroha populations), but more rectangular in specimens from southern populations (e.g., Ruahine Ranges) with slight dorsal hump ( Fig. 63 LP), steep slope (60°) to arm; arm short and narrow, ventral edge of arm curved anterad; terminal lobe short and narrow with apical tuft of long setae ( Fig. 63 LP); a long comb of setae at arm-basal lobe junction, setae shortened along apical portion of basal lobe ( Fig. 63 LP), ventral edge straight. Right paramere an elongated, narrowly triangular with a double row of long setae along apical ½ of ventral edge (e.g., Mt Te Aroha), apical ¾ of ventral edge (e.g., Ruahine Ranges) ( Fig. 63 RP), apical portion strongly inwardly curved across penis lobe.

Female genitalia: Basal gonocoxite 1 long and broad (especially apically), ventral surface with a few rugose wrinkles, internal dorso-lateral carina with 1 seta (e.g., Ruahine Ranges) or 3 setae (e.g., Mt Te Aroha). Gonocoxite 2 elongate and narrowed, ventral surface with rugose wrinkling, dorsal edge slightly reflexed. Ramus ( Fig. 5 ) very long and broad.

Comments: Britton’s (1949) illustration of the apical portion of the penis lobe best matches that of the eastern Ruahine Ranges population. Most populations have minor variations in external morphology, but the apical penis lobe shape and endophallus structures remain constant throughout the distribution.

Distribution: New Zealand, North Island, Mt Ruapehu, Pureora Forest, Mt Te Aroha, Kauaeranga Valley, Kaimai Ranges, Lake Waikaremoana and northern Hawke’s Bay, Kaweka and Ruahine Ranges.

Holotype: BMNH specimen labelled. Type [round label with red border] / 4255 [hw] / New Zeal. [red underline] Broun Coll. Brit. Mus. 1922-482 / Ohakune 30-12-1910 [hw] / Mecodema validum [hw].

Material examined: 1♂, Tongariro National Park , viii. 1962 M.B. Paterson [hw] / M.B. Paterson Collection / AMNZ 40821 ; 1♂, NEW ZEALAND HB, Boundary Stream Mainland Island , BSMI8.1 , 12 Dec 1998 – 12 Jan 1999 DoC ( NZAC) ; 1♂, 1♀, Mt Te Aroha under plank, 23 Dec 67, J.S. Dugdale [hw] ( NZAC) ; 1♂, NEW ZEALAND TO Pureora FP Link Rd, Mt Pureora tk (start of tk), 23.XII.1995 – 3.I.1996 Larochelle.Larivière / Wet rimu forest pittraps ( NZAC); 1, Lake Waikaremoana, N.Z., L. Ruapani 3000 ft. under log. 16–23:xi:1958 J.C. Watt / J.C. Watt Collection / Mecodema validum Broun 1923 Det. A. Larochelle / mites on specimen [orange label] ( NZAC) .

Figures

FIGURE 2. Ventral view of a Mecodema specimen showing specific morphological structures, excluding taxonomic structures indicated in detail figures, used in the species descriptions. ƑLF = ventrite lateral foveae; ƑSP = ventrite setose punctures; MTC = metacoxa; MTƑP = metaventrite process; MSC = mesocoxa; PC = procoxa; PS = prosternum; G = gena; PES = proepisternum; MSE = mesepisternum; MTE = metepisternum; Ƒ1–Ƒ6 = ventrites 1-6 (ventrites 1-3 may be fused); M = midline (dashed line, not a taxonomic structure).

FIGURE 4. An Environmental Scanning Electron Microscope (ESEM) photograph of the four main structures of the apical plate of the endophallus within the penis lobe. This is an example from Mecodema haunoho showing the central spicule (c.s), left (l.s.f) and the right setose flange (r.s.f), and microtrichial field (m.f). These structures are variable among species but within a species, they are very consistent, even over distant geographical ranges. The microtrichial field can be covered in flattened scales as in photo above, or with elongated setae-like scales.

FIGURE 5. The entire female reproductive tract (ventral view) including taxonomic structures (for all other abbreviated structure names see Seldon et al. 2012). However, for this revision only the following structures are important: HS = helminthoid sclerite; G1 = gonocoxite 1; G2 = gonocoxite 2; TDC = transverse dorsal carina; R = ramus.

FIGURE 6. Detail of the three different forms of the elytral humeral angle: (A) = anteriorly convergent (M. parataiko), (B) = evenly convex (M. oconnori), (C) = subangulate (M. atuanui).

FIGURE 8. Detail of the ventral head with the taxonomic structures used in the species descriptions. SBMS = submentum setae; SBM = submentum sclerite; ML = mentum lobe; MP = mentum process (with indentation); MPW = mentum process width; SBS = stipes basal setae; MPL = mentum process length; MPS = mentum process setae; SBMC = submentum sclerite constriction; GP = gula pits; GS = gula suture.

FIGURE 9. Dorsal view of head with detail of the morphological structures used in the species descriptions. Ƒ = vertex; SPS = supraorbital puncture setae; SP = supraorbital puncture; F = frons area; FCS = frontoclypeal suture; C = clypeus; M = mandible; LS = labrum setae; L = labrum; ACM = anterior clypeal microsculpture; CSP = clypeal setose puncture; TP = tentorial pit; SG = supraorbital grooves; E = eye; ƑG = vertexal groove.

FIGURE 10. The protibia form is a character used mainly to determine between genera, except for one species in Mecodema where the difference between (A) greatly distally expanded (M. antarctica) and (B) expanded distally (all other Mecodema species) is used.

FIGURE 12. Ventral view of the mentum with a number of different character states. Illustrations A–D are the different forms of the indentation in the apex of the median process: (A) distinctly indentate (M. manaia); (B) moderately indentate (M. pluto); (C) slightly indentate (M. infimate); (D) indentation notched (M. parataiko). Illustrations E–G are the three general forms (i.e., hashed lines) of the mentum lobes: (E) triangular; (F) rounded; (G) squared.

FIGURE 14. Diagrammatic cross sections that represent the width and convexity of head or deflection of pronotum (frontal view): (A) broad and flat; (B) broad and convex; (C) narrow and flat; (D) narrow and convex.

FIGURE 15. The penis lobe in ventral view showing the relative deflection to right of vertical: (A) distinctly deflected (M. regulus); (B) moderately deflected (M. haunoho); (C) slightly deflected (M. oregoides). Scale bars = 1 mm. Structures of penis lobe indicated are: base (B); lateral edge (LE); apical portion (AP); ventral edge (ƑE).

FIGURE 16. Relative strength of the ventral curve over the length of the penis lobe (lateral view): (A) slightly curved (M. oblongum); (B) moderately curved (M. ponaiti); (C) distinctly curved (M. manaia). Scale bar = 1 mm.

FIGURE 63. Mecodema validum plate with half habitus (left) and the three (detached) structures of the male aedeagus: the right (RP) and left parameres (LP), plus the penis lobe (PL). The bottom scale bar is the width across the widest point of the pronotum of the specimen used for this habitus and top scale bar equates to the half the length of the penis lobe.