Mecodema argentum, 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 : 27-29

Mecodema argentum sp. n.

Figure 19 .

Diagnosis: Distinguishable from other North Island Mecodema species by having: 1, a very broad and flat head; 2, elytral interval 7 flat; 3, the apical shape of the penis lobe and form of left paramere distinctive ( Figs 19 PL and 19LP).

Description: Length 29–32 mm, pronotal width 7.4–8.9 mm, elytral width 8.5–10 mm. Colour of entire body matte black, except coxae bright reddish-brown, legs matte dark reddish-brown.

Head: Very broad and flat. Vertex smooth, except very fine wrinkles sparsely distributed laterally ( Fig. 19 ); vertexal groove broad and shallow, more impressed laterally (micropunctate and small shallow grooves occassionally present); large supraorbital puncture bearing 4–5 setae; 4–6 poorly defined supraorbital grooves above and anterad eyes, extended onto lateral area of frons; frons ( Fig. 9 ) with a large and shallow depression each side of midline; frontoclypeal suture more defined laterally, obscured by raised hump medially of frons-clypeus junction, tentorial pits indistinct; anterior area of clypeus with a setose puncture each side bearing 2 setae, central groove with a large setose puncture bearing 2–3 setae (central puncture may be absent). Labrum rounded laterally, anterior edge straight, slightly emarginated with 2 proximate central setae, 2 setae each side evenly spaced. Mentum lobes rounded ( Fig. 12F ), median process very broad and short, slightly angled upward (15°), moderately indentate ( Fig. 12B ); mentum setae absent. Submentum sclerite constriction narrow, strongly folded with 6 evenly distributed setae. Stipes with 2 basal setae. Gula pits small, suture defined, gula flat and smooth. Gena ( Fig. 8 ) with rugose, transverse wrinkles forming an isodiametric pattern laterally.

Prothorax: Prothoracic carina narrow the entire length, slightly crenulated with 8–12 setae each side ( Fig. 19 ), extended beyond anterior angle; posterior lateral sinuation evidently carinate, parallel; pronotum very broad and flattened, overall shape broadly cordate; midline narrowly defined with anterior medial triangular impression and posterior medial diamond-shaped impression present, disc with transverse wrinkles laterally; pronotal foveae deep and broad; anterior and posterior edges straight. Prosternum ( Fig. 2 ) flat with very fine transverse lines; proepisternum without microsculpture. Procoxal setae absent; protibia distally expanded and shovel-like ( Fig. 10B ).

Elytra: Broad and flattened, slightly deflected laterally; humeral angle evenly convex ( Fig. 6B ); basal margin slightly curved and gently sloped to base, interval 1 extended to scutellum, other intervals and striae extended to margin ( Fig. 19 ); lateral carina narrow the entire length, extended beyond humeral angle; humerus with 3–4 closely distributed anterior setose punctures, 4 th or 5 th puncture double-spaced posterad; suture less impressed than striae; striae with small, regularly distributed, asetose punctures, increasing in size laterally, all equally impressed (visible to naked eye); intervals relatively flat but convexity slightly increased laterally; interval microsculpture absent; 7 th strial setal pattern ( Fig. 1 ) with 3 setae in anterior ½, 4–5 setae in posterior ½, setose punctures small.

Ventral surface: Mesepisternum and metepisternum without microsculpture; setose punctures present on mesocoxae (2) and metacoxae (2). Abdominal ventrite 1 lineate (sparsely); ventrite 2 ( Fig. 2 ) finely lineate, may have fine pitting interspersed close to metacoxae; ventrites 3–5 with 1 setose puncture each side of midline; ventrite 6 setae present: ♂ with 1 setose puncture each side of midline, ♀ with 2–3 setose punctures each side located at junction of bluntly-rounded apical edge and curve anterad; ventrites 4 and 5 may be foveate laterally. Anterior metaventrite process ( Fig. 2 ) a triangle with a very broad carina the entire length.

Male genitalia: Apical portion of penis lobe asymmetrically hooked, short apical portion with slight deflection to right of vertical axis (VV) ( Fig. 15C ); apex shape narrow the entire length and perpendicular ( Figs 3 and 19 PL), ventral process curved downward to form a rounded point, then curved upward to form the dorsal process that is a very short, rounded hook (almost hammer-like); penis lobe shaft of equally narrow the entire length ( Fig. 19 PL), ventral edge straight (VV), overall length of the penis lobe distinctly 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 is extensive (76–100%); left setose flange is large; right setose flange is absent. Left paramere basal lobe a large rectangle-shape, with very pronounced anterior hump forming a steep angle (almost perpendicular) to the very short and narrow arm ( Fig. 19 LP); narrow terminal lobe; a few short setae extended from apex, then setae increased in length to mid-arm; longer setae extended from ½ way along arm to anterior region of basal lobe ( Fig. 19 LP); ventral edge of basal lobe relatively straight. Right paramere narrow and triangular in shape, slightly longer with very long setae extended along apical ½ of ventral edge ( Fig. 19 RP); apical ⅓ slightly inwardly curved.

Female genitalia: Basal gonocoxite 1 long and broad at base, but very broad toward gonocoxite 2 with 3–4 well-defined grooves (wrinkles); internal dorso-lateral carina with 3 short robust setae at ventral apex dorsad gonocoxite 2. Gonocoxite 2 triangular, broad basally, narrowed and rounded apically. Ramus ( Fig. 5 ) long and narrow.

Comments: The southern distributional limit along the the Coromandel Peninsula of Mecodema argentum remains unclear, but there are other large broscines present in this area. Mecodema validum is present in the Kauaeranga Valley and Mt Te Aroha, i.e. the southern areas of the Coromandel Peninsula. The widespread species, M. crenaticolle , is present as far north as the Tapu-Coroglen Rd, and M. atrox (a coastal forest dweller) has been collected at Kennedy Bay. However, M. argentum has more shared characters with north Auckland and Northland species, like that of the curvidens species group (see Seldon & Leschen 2011), than the Mecodema species of the Waikato and Bay of Plenty.

Distribution: New Zealand, North Island, northern Coromandel Range, Coromandel town, Trig Tk.

Holotype: NZAC male labelled. Coromandel Ra. 3½ km N. of Coromandel 13.1.93 G.Shirley / HOLOTYPE Mecodema argentum n. sp. design. DS Seldon, TR Buckley 2018.

Paratypes: 2♂, 1♀ NEW ZEALAND, CL, Coromandel Ra., Coromandel town , Trig T Tk, PTs 8–28 Feb 2014, DS Seldon / CAR 159 ♂; CAR 205 ♂; CAR 206 ♀ ( AMNZ) ; 1♂, Kauri Grove Coromandel-Coroglen Rd 22- 1-60 J.I. Townsend [hw] ( NZAC) ; 1♂, Mainridge Pitoki Stream 3 km ESE of Coromandel 13.1.93 G. Sherley [hw] ( NZAC) .

Etymology: Argentum is Latin for silver, and therefore, Mecodema argentum is named for my good friend Silver Bishop. Silver reminded me a few years ago that I promised to name a species after her when I got the chance, so I’m fulfilling that promise. The name is to be treated as a noun in apposition.

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 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 19. Mecodema argentum 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.