Mecodema atrox Britton, 1949

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 : 29-31

Mecodema atrox Britton, 1949 .

Figure 20 .

Diagnosis: Mecodema atrox is within the curvidens group species based on having less than or equal to six setae each side along the pronotal carina. It differs from other North Island curvidens group species by having: 1, the sides of the pronotum rounded anteriorly and posteriorly (looks truncated); 2, the elytral striae have defined asetose punctures their entire length; 3, left paramere lobe form, distribution and length of setae along apical ¾ of ventral edge are distinctive ( Fig. 20 LP).

Description: Length 17–24 mm, pronotal width 4.5–6 mm, elytral width 6–8 mm. Colour of entire body black, except coxae and legs are dark reddish-brown.

Head: Narrow and flat ( Fig. 14C ). Vertex smooth; vertexal groove ( Fig. 9 ) narrow and defined entire length; large supraorbital puncture bearing 3–4 setae; 2 deep and short supraorbital grooves mesad of puncture; frons smooth; frontoclypeal suture well-defined, very small tentorial pits; anterior area of clypeus ( Fig. 9 ) narrowly grooved; clypeus with 1 setose puncture each side bearing 2 setae. Labrum rounded but angled laterally, anterior edge rounded, forming a gentle curve inward medially with 3 regularly-spaced setae each side. Mentum lobes squared ( Fig. 12G ), mentum process narrow and long, broad at base, slightly angled upward (15°), strongly indentate ( Fig. 12A ); mentum setae present (occassionally absent). Submentum sclerite constriction broad with 6 setae, 2 ventrad fold and 1 very close to edge. Stipes with 2 basal setae. Gula pits ( Fig. 8 ) small, suture defined, gula flat and smooth. Gena with very fine isodiametric wrinkles across entire area.

Prothorax: Prothoracic carina narrow the entire length, slightly crenulated with 4–5 setae each side ( Fig. 20 ), extended beyond anterior angle; posterior lateral sinuation indistinctly carinate, parallel; pronotum broad and flattened, deflected to carina, overall shape cordate; midline slightly impressed, medial impressions absent, transverse wrinkles may be present laterally on disc ( Fig. 20 ); pronotal foveae shallow and narrow; anterior edge strongly inwardly curved, posterior edge straight. Prosternum flat, may have widely-spaced, very light transverse lines; proepisternum without microsculpture. Procoxal setae absent; protibia distally expanded and shovel-like ( Fig. 10B ).

Elytra: Broad and flat; humeral angle anteriorly convergent ( Fig. 6A ); basal margin is slightly curved and gently sloped to base, all striae and intervals terminated at margin; lateral carina narrow the entire length, extended to humeral angle; humerus with 2 asetose pits and 1 setose puncture; suture ( Fig. 1 ) indistinct; striae with small, regularly distributed, asetose punctures increased slightly in size laterally and near apex; intervals 1–4 flat to weakly convex, convexity slightly increased laterally; interval microsculpture absent; 7 th strial setal pattern with 0–1 setose puncture in anterior ½, 3 setose punctures in posterior ½, setose punctures small.

Ventral surface: Mesepisternum ( Fig. 2 ) and metepisternum without microsculpture; setose punctures of mesocoxa present (1) and metacoxa (0). Abdominal ventrites 1–5 finely wrinkled; ventrites 4 and 5 with 1 setose puncture each side of midline; ventrite 6 setae present ( Fig. 2 ): ♂ with 2–3 setae in broad pits located each side at the junction of the straight apical edge and curve anterad, ♀ with 2–4 setae in broad pits on either side of bluntlypointed apical edge, an extra setae may be present, but set back from edge; lateral foveae on ventrites absent. Anterior metaventrite process triangular with a broadly rounded apex, carina broad the entire length.

Male genitalia: Apical portion of penis lobe asymmetrically rounded, but the ventral edge is extended slightly forward of the vertical central line ( Fig. 3 ) giving the apex an angulate curve toward the dorsal edge ( Fig. 20 PL), apical portion of penis lobe with a distinct deflection to right of vertical axis (VV) ( Fig. 15A ); shaft of penis lobe equally broad and relatively straight (VV); overall length of penis lobe straight for apical ½, then slightly to moderately 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 narrow and short; setal (scales) coverage of the apical plate sparse (1–25%); left setose flange small; right setose flange large. Left paramere basal lobe rectangular and relatively narrow ( Fig. 20 LP), anterior slope slightly angled (15°) to form the arm; arm long and very wide (½ width of body); terminal lobe large with double row of very long setae; ventral edge of main body straight; double row of medium length setae extended along ventral edge from arm to ¾ of edge ( Fig. 20 LP). Right paramere very narrow, approx. ½ width of left paramere ( Fig. 20 RP); long and narrow arm with terminal lobe indistinct from arm, double-row of long setae extended along apical ¾ of ventral edge, setae longer at lobe and midway along edge.

Female genitalia: Basal gonocoxite 1 ( Fig. 5 ) long and narrow, ventral surface with a few wrinkles, surface with many scattered sensillar pits; internal dorso-lateral carina with 3 setae. Gonocoxite 2 bluntly rounded apically, broadly triangular at base, apical portion bent outwards with numerous sensillar pits. Ramus long, narrowed apically.

Comments: This species was described by Britton (1949) based on a single badly damaged male specimen. Mecodema atrox is found in coastal native forests on the lower slopes of the Coromandel Ranges, northern Kaimai Ranges and is closely related to M. curvidens ( Seldon et al. 2012) . Mecodema atrox has been listed by the Department of Conservation as threatened to critically-endangered due to habitat loss and predation by introduced mammals. Extensive pitfall trapping since 2004 in remnant coastal forest has failed to collect any specimens.

Distribution: New Zealand, North Island, Coromandel Peninsula, northern Kaimai Range, coastal forests.

Holotype: NZAC male labelled. Type [round label with red border] / Tauranga N.Z. 20-26 - 3-31 E.S. Gourlay / HOLOTYPE Mecodema atrox n. sp. [hw] E.B. Britton. det. 1946 [date hw] / E.S. Gourlay Acc. 1970 Ent. Div. / NZAC 04011260. Paratypes: (see Seldon & Leschen 2011; Britton 1949).

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 3. Detail of the apical portion of aedeagus (male genitalia) with parameres removed showing taxonomic structures, vertical and horizontal planes that are referred to in the species descriptions and redescriptions: aedeagus shaft width (ASW); vertical central line (ƑCL) [dashed line, not a structure]; horizontal central line (HCL) [dashed line, not a 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 20. Mecodema atrox 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.