Mecodema curvidens Broun, 1915

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 : 39-41

Mecodema curvidens Broun, 1915 .

Figures 12G and 24 .

Metaglymma curvidens Broun, 1915 (Opotiki, BP), synonymised by Britton 1949.

Mecodema occiputale Broun, 1923 (Tokaanu, TO), new synonymy.

Mecodema exitiosus Brookes, 1926 (nr. Matamata, WO), synonymised by Britton 1949.

Diagnosis: Distinguished from other North Island Mecodema species by having: 1, pronotal carina with 4–6 setae each side ( curvidens species group); 2, a vertexal groove that is narrow and defined entire length; 3, distinctive form of the basal lobe and setal distribution along ventral edge of the left paramere ( Fig. 24 LP).

Description: Length 18–26 mm, pronotal width 5.4–7.53 mm, elytral width 6.13–8.56 mm. Colour of entire body glossy to matte black, except coxae to tarsi reddish-brown to black.

Head: Broad and flat ( Fig. 14A ). Vertex smooth ( Fig. 9 ); vertexal groove narrow and defined entire length; large supraorbital puncture bearing 3–4 setae; 4 supraorbital grooves slightly impressed, extended onto lateral area of frons; frons smooth; frontoclypeal suture well-defined the entire length, tentorial pits small; anterior area of clypeus narrowly grooved (may be indistinct), 1 large, setose puncture each side bearing 2 setae. Labrum rounded, anterior edge straight with 3 evenly spaced setae each side. Mentum lobes squared ( Fig. 12G ), median process broad at base narrowed (long) to apex, upward angle absent, distinctly indentate ( Fig. 12A ); mentum setae present. Submentum sclerite constriction ( Fig. 8 ) narrow with 3 setae clustered each side (large gap medially). Stipes with 2 basal setae. Gula ( Fig. 8 ) pits small, suture indistinct, gula flat and smooth. Gena with fine wrinkles forming an isodiametric pattern across entire area.

Prothorax: Prothoracic carina narrow the entire length, slightly crenulated with 4–7 setae each side ( Fig. 24 ), extended beyond anterior angle; posterior lateral sinuation indistinctly to evidently carinate, parallel; pronotum broad and flattened, overall shape squared ( Fig. 24 ); midline well-defined, medial impressions absent, very fine, transverse lines that may be present laterally on disc; pronotal foveae shallow and narrow; anterior edge inwardly curved and posterior edge relatively straight. Prosternum ( Fig. 2 ) weakly convex and smooth; proepisternum without microsculpture. Procoxal setae absent; protibia distally expanded and shovel-like ( Fig 10B ).

Elytra: Narrow and flat; humeral angle anteriorly convergent (making elytra look narrow at base) ( Fig. 6A ); basal margin slightly curved (almost straight) and bevelled to base, interval 1 extended to scutellum, other intervals and striae terminated at margin; lateral carina narrow the entire length, extended to humeral angle; humerus with 2 setose punctures proximate angle; suture well-defined, slightly broadened at humeral angle; striae with small, regularly distributed, asetose punctures, slightly increased in size laterally; intervals 1–4 flat, intervals 5–9 weakly convex (convexity increased laterally); interval microsculpture absent; 7 th strial setal pattern ( Fig. 1 ) with 0–1 setose puncture in anterior ½, 3–4 setose punctures in posterior ½, setose punctures large.

Ventral surface: Mesepisternum and metepisternum with fine wrinkles; setose punctures present on mesocoxae (1) and metacoxae (0). All abdominal ventrites finely lineate laterally; ventrites 1–3 setose without punctures, ventrites 4 and 5 with 1 setose puncture each side of midline; ventrite 6 ( Fig. 2 ) setae present: ♂ with 2 setae each side at junction of the apical edge flattened curve and curve anterad, ♀ with 4 setae each side, apical edge a pointed curve; lateral foveae absent. Anterior metaventrite process ( Fig. 2 ) a long and rounded triangle without carina.

Male genitalia: Apical portion of penis lobe symmetrically rounded ( Fig. 24 PL) but with a flattened curve at the apex, slight deflection to right of vertical axis (VV) ( Fig. 15C ); penis lobe shaft straight the entire length (VV), shaft width equally narrow from apex to base, overall length of penis lobe distinctly curved ventrally (LV) ( Fig. 16C ). Structures of the endophallus ( Fig. 4 ): lateral form of the apex of the central spicule rounded; dorsal form of the apex of the central spicule short and narrow; setal (scales) coverage of the apical plate is sparse to moderate (1–25%); size of left setose flange small; size of right setose flange large. Left paramere basal lobe small (may be slightly larger in specimens of some populations), rectangular with a long and gentle slope (15°) to arm; arm relatively large (½ of whole paramere), gradually narrowed to terminal lobe ( Fig. 24 LP); terminal lobe not distinct from arm, apical tuft of elongate setae, medium lengthed setae continue along apical ¾ of ventral edge. Right paramere narrowly triangular with medium to long setae extending along apical ¾ of ventral edge ( Fig. 24 RP).

Female genitalia: Basal gonocoxite 1 short and broad, flattened apically, large shallow groove on inward side, internal latero-dorsal carina without setae. Gonocoxite 2 ( Fig. 5 ) bluntly rounded and triangular. Ramus very long and narrow.

Comments. Mecodema curvidens and M. occiputale were described by Broun from badly damaged specimens in 1915 and 1923 respectively. Seldon & Leschen (2011) commented on the similarities in morphology and distribution, with M. curvidens being found more often on the eastern slopes of the Kaimai Ranges and coastal forest remnants, whereas M. occiputale is widespread across the Central Plateau. Further morphological investigations and the discovery of populations in northwestern Hawke’s Bay and East Cape have shown that these two species are actually one widespread species, with distinctive ecotypes.

Distribution: New Zealand, North Island, Coromandel, Bay of Plenty, Hawke’s Bay, Taupo, Waikato, Whanganui.

Holotype ( Metaglymma curvidens ): BMNH. 3683. [hw] / New Zeal. [red underlined] Broun Coll. Brit. Mus. 1923-482. / Opotiki. Decr. 1912. [hw] / Metaglymma curvidens . ♀. [hw] / HOLOTYPE Metaglymma curvidens Broun confirmed by Seldon and Leschen 2010 [red label].

Lectotype ( Mecodema occiputale ): BMNH. Para-type [round label with yellow border] / 4256 [hw] / New Zeal. [red line beneath NZ] Broun Coll. Brit. Mus. 1922-482. / Tokaanau. 6.4.1918. [hw] / Mecodema , occiputale. [hw] / LECTOTYPE Mecodema occiputale Broun design. by Seldon & Leschen 2010 [red label].

Paratype ( Mecodema exitiosus ): NZAC. Okauia 16.1.21 [hw] / Holotype (faded orange label) [hw] / Mecodema exitiosus Brookes [hw] / NZ Arthropod Collection NZAC 04011128 .

Material examined: 1, NEW ZEALAND HB Boundary Stream Mainland Island , Kamahi Loop Tk, under logs, 4 Jan 2011, D.S. Seldon / Podocarp-kamahi canopy, E2839579 N6225723 ( NZAC) ; 1, NEW ZEALAND HB/ TO State Highway 5, Oputo Falls S.R., 20–28 Dec 2015, D.S. Seldon / Podocarp-broadleaf canopy, pitfall traps, S38°58’55.2 E176°32’00.4, 552 m ( NZAC) ; 1, NEW ZEALAND, HB, Puketitiri , Ball’s Clearing, 19–30 Dec 2015, D.S. Seldon, J. Tizard / Podocarp-broadleaf canopy, 30 pitfall traps, S39°16’15.7 E176°29’55.4 ( NZAC) .

Figures

FIGURE 1. Dorsal view of a Mecodema specimen showing taxonomic structures used in the species descriptions. H =head; P = pronotum; E = elytra; S = striae; I1 = interval 1; A = apex; 7S = 7 th strial setae; HSP = humerus setose puncture; HA = humeral angle; BM = basal margin; P = protibia.

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 24. Mecodema curvidens 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.