Mecodema ngaiatonga, Seldon & Buckley, 2019

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 : 76-78

Mecodema ngaiatonga , sp. n.

Figure 40 .

Diagnosis: Different from other North Island Mecodema species by the following: 1, vertex smooth and vertexal groove indistinct, may have obsolescent punctures laterally; 2, elytral interval 9 strongly convex; 3, anterior metaventrite process a squat rounded triangle with apically broad to basally narrow carina; 4, distinctive shape of the apical portion of the penis lobe ( Fig. 40 PL).

Description: Length 26.9–33 mm, pronotal width 7.2–9.4 mm, elytral width 8.3–10.4 mm. Colour of entire body matte to glossy black (may be reddish-brown).

Head: Broad and flat ( Fig. 14A ). Vertex smooth; vertexal groove indistinct, in some obsolescent punctures present laterally ( Fig. 40 ); small supraorbital puncture bearing 4–5 setae; 3–4 poorly defined supraorbital grooves extended to lateral edge of frons; frons medially convex with a large and shallow depression each side, may have shallow grooves present within depressions; frontoclypeal suture indistinct, tentorial pits absent; anterior area of clypeus with 3 broad and shallow grooves, 1 large setose puncture each side bearing 2 setae, central puncture bearing 2 setae may be present. Labrum lobate, anterior edge moderately emarginated with 2 proximate central setae, 2 setae each side evenly spaced. Mentum lobes rounded ( Fig. 12F ), median process very short and broad, slightly angled upward (15°), strongly indentate ( Fig. 12A ); mentum setae absent. Submentum sclerite constriction broad with 6–8 evenly spaced setae. Stipes with 2 basal setae. Gula pits small, suture indistinct, gula flat with transverse lines present. Gena ( Fig. 8 ) with fine lines forming an isodiametric pattern across entire area.

Prothorax: Prothoracic carina broad the entire length, crenulations absent with 6–10 setae each side, extended beyond anterior angle; posterior lateral sinuation evidently carinate, slightly angled inward; pronotum broad but deflected laterally, overall shape rounded to triangular cordate ( Fig. 40 ); midline impressed, anterior medial triangular impression and posterior medial diamond-shaped impression present, disc with fine transverse wrinkles laterally ( Fig. 40 ); pronotal foveae narrow and shallow; anterior edge inwardly curved, posterior edge straight. Prosternum ( Fig. 2 ) flat with fine, widely spaced transverse lines; proepisternum without microsculpture. Procoxal setae absent; protibia distally expanded and shovel-like ( Fig. 10B ).

Elytra: Narrow and moderately deflected; humeral angle evenly convex ( Fig. 6B ); basal margin moderately curved and gently sloped to base, interval 1 extended to basal margin; lateral carina broad in anterior and posterior ⅓, medially ⅓ narrowed, extended beyond humeral angle; humerus with 3–4 setose punctures; suture impressed entire length; striae with regularly spaced, small asetose punctures ( Fig. 40 ), slightly increased in size laterally; intervals 1–4 weakly convex; intervals 5–8 moderately convex; interval 9 strongly convex; interval microsculpture present as fine transverse wrinkles; 7 th strial setal pattern with 3–4 setose punctures in anterior ½, 4–5 setose punctures in posterior ½ ( Fig. 40 ), setose punctures large.

Ventral surface: Mesepisternum with rugose wrinkles; metepisternum without microsculpture; setose punctures present on mesocoxa (2) and metacoxa (2). All abdominal ventrites finely lineate laterally; ventrites 3–5 with a single setose puncture each side of midline; ventrite 6 setae present ( Fig. 2 ): ♂ and ♀ with 2–3 closely spaced setae in large punctures each side of midline along straight portion of apical edge; ventrites 3–5 foveate laterally (very shallow). Anterior metaventrite process a squatly rounded triangle with an apically broad to basally narrowed carina.

Male genitalia: Apical portion of penis lobe asymmetrically double-hooked with slight deflection to right of vertical (VV) ( Fig. 15C ); a very slight curve downward (from shaft) to form the short and pointed ventral process, apex curved symmetrically upward to form a long, narrow and rounded dorsal process ( Fig. 40 PL), slightly recurved, then evenly curved downward to rejoin shaft; shaft of penis lobe of equally narrow width, gradually broadened toward base, apical ¼ of ventral edge with moderate curve to right (VV), overall length of penis lobe slightly curved ventrally (LV) ( Fig. 16C ). 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 moderate (26–75%); size of left setose flange small; size of right setose flange absent. Left paramere basal lobe a small, rounded rectangle with a moderately sized anterior hump forming a steep (60°) slope to a short and narrow arm; terminal lobe slightly broadened with apical tuft of short setae ( Fig. 40 LP), then very short and sparse setae to long-lengthed setal fringe in arm-basal lobe junction through to anterior part of basal lobe, setae extended along apical ⅓ of ventral edge; ventral edge of basal lobe straight, curved to meet arm ( Fig. 40 LP). Right paramere with long and narrow arm, twice as long as squared basal lobe (equal overall length to left paramere), a double row of very long setae extended along apical ¾ of ventral edge ( Fig. 40 RP), only apical portion inwardly curved toward penis lobe.

Female genitalia: Basal gonocoxite 1 short and broad, ventral surface without rugose wrinkles or grooves; internal dorso-lateral carina with 1 seta. Gonocoxite 2 ( Fig. 5 ) narrowly triangular. Ramus long and broad.

Comments: Mecodema ngaiatonga is a large-bodied species found throughout Russell Forest. Although relatively abundant it could soon be threatened by an influx of destructive feral pigs within Russell Forest.

Distribution: New Zealand, North Island, Northland, Russell Forest (Ngaiatonga).

Holotype: NZAC male labelled. NEW ZEALAND ND, Ngaiatonga Saddle 16 Jul 1983 J.C. Watt [hw] / HOLOTYPE Mecodema ngaiatonga n. sp. design. DS Seldon, TR Buckley 2018 [red label].

Paratypes: 1♀, Ngaiatonga Bush, S th of Russell, N. Auckland [hw] / 29.Dec.60 J.C. Watt [hw] / under logs; 1, 2224 Russell, Ngaiatonga Scenic Reserve Johns PM 1 xi 95 logs / 2007. 163. 10893 ( CMNZ) ; 1♀, NZ ND Russell For., Punaruku Stream 24.XII.1992 A. Larochelle / Manuka (mostly)-tree ferns Pittraps ( NZAC); 1, NZ ND Russell For., Ngaiatonga Walkway 24.XII.1992 A. Larochelle ( NZAC); 2244 Russell, Ngaiatonga Scenic Reserve Johns, PM 1.xi.95 logs / 2007.163.10893 ( CMNZ) .

Etymology: Mecodema ngaiatonga is named after the type locality, Ngaiatonga (Russell) Forest S.R.

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 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 40. Mecodema ngaiatonga 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.