Mecodema regulus Britton, 1964

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 : 99-101

Mecodema regulus Britton, 1964 .

Figures 15A and 50 .

Diagnosis: Differs from other North Island Mecodema species by: 1, 4-6 setae along pronotal carina ( curvidens species group); 2, vertexal groove narrow and well-defined with a distinctive V-shape medially; 3, metacoxa without setose punctures; 4, distinctive shape of the left paramere ( Fig. 50 LP).

Description: Length 22–28.1 mm, pronotal width 6.6–8.5 mm, elytral width 8–10 mm. Colour of entire body matte to glossy black.

Head: Broad and flat ( Fig. 14A ). Vertex smooth; vertexal groove narrow, well-defined the entire length with a V-shape medially ( Fig. 50 ); large supraorbital puncture bearing 2–3 setae; 1 well-defined supraorbital groove; frons very flat and smooth; frontoclypeal suture well-defined between small tentorial pits; anterior area of clypeus flat and smooth, microsculpture indistinct; clypeus with 1 setose puncture on each side bearing 1–2 setae ( Fig. 50 ). Labrum rounded laterally, anterior edge outwardly curved, slightly emarginated medially with 2 proximate central setae, 2 setae each side evenly spaced. Mentum lobes rounded ( Fig. 12F ), median process broad to narrow (apically) and short, slightly angled upward (15°), notched indentation ( Fig. 12D ); mentum setae present. Submentum sclerite constriction narrow with 4–6 setae clustered laterally. Stipes with 2 basal setae. Gula pits small in deep depression, suture defined, gula ( Fig. 8 ) flat with very fine transverse wrinkles. Gena with very fine wrinkles forming an isodiametric pattern across entire area.

Prothorax: Prothoracic carina broad the entire length, crenulation may be present with 4–5 setae each side ( Fig. 50 ), extended beyond anterior angle ( Fig. 11 ); posterior lateral sinuation evidently carinate, inwardly angled; pronotum broad and flattened, overall shape cordate ( Fig. 50 ); midline well-defined, disc with very fine and sparsely distributed transverse wrinkles laterally; pronotal foveae deep and broad; anterior edge slightly inwardly curved, posterior edge straight. Prosternum flat with fine transverse wrinkles, small depressions laterally; proepisternum without microsculpture. Procoxal setae absent; protibia distally expanded and shovel-like ( Fig. 10B ).

Elytra: Broad and flattened; humeral angle anteriorly convergent ( Fig. 6A ); basal margin slightly curved and bevelled to base, all intervals and striae truncated at margin; lateral carina narrow the entire length, extended to humeral angle; humerus with 1–2 setose punctures ( Fig. 50 ), indistinct raised carina around punctures in line with the basal end of stria 7; suture well-defined, but no more so than striae; striae with small, regularly distributed, asetose punctures, slightly increased in size and depth laterally ( Fig. 50 ); all intervals with weak convexity the entire length; intervals without microsculpture; 7 th strial setal pattern with 1 setose puncture in anterior ½, 3–4 well spaced long setae in posterior ½ only ( Fig. 50 ), setose punctures small.

Ventral surface: Mesepisternum ( Fig. 2 ) and metepisternum without microsculpture; setose punctures of mesocoxae ( Fig. 2 ) absent and present on metacoxae (1). Abdominal ventrites 1–5 without setose punctures and microsculpture; all ventrites without lateral foveae; ventrite 6 setae present: ♂ with 2 proximate setose punctures each side positioned laterally ventrite angled edge; ♀ with 2 setose punctures each side, distantly spaced and located anterad ventrite angled edge. Anterior metaventrite process an apically broad triangle with a poorly defined carina.

Male genitalia: Apical portion of penis lobe symmetrically rounded ( Fig. 50 PL), apical curve flat, distinct deflection to right of vertical axis (VV) ( Fig. 15A ); shaft of penis lobe narrow and equal width the entire length, ventral edge of shaft with weak curve to left (due to distinct apical deflection) (VV); overall length of penis lobe moderately curved ventrally (LV) ( Fig. 16B ). 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 short and narrow; setal (scales) coverage of the apical plate sparse (1–25%); size of left setose flange small; size of right setose flange large. Left paramere basal lobe ovate with a short slope to arm ( Fig. 50 LP); arm short and broad, narrowed to terminus; terminal lobe indistinct from arm, apical tuft of long setae, medium-lengthed setae extended along apical ½ of ventral edge; ventral edge straight ( Fig. 50 LP). Right paramere long and narrowly rectangular, setae extended along apical ¾ of ventral edge ( Fig. 50 RP).

Female genitalia: Basal gonocoxite 1 short and broad, apically broadened, ventral surface entirely covered with rugose wrinkles, internal dorso-lateral carina ( Fig. 5 ) with 5 setae. Gonocoxite 2 short, bluntly rounded and triangular. Ramus short and narrow.

Comments: Mecodema regulus is found on all of the large islands in the Three Kings group, and is more closely related to M. ponaiti (Poor Knights Is.) , than to the geographically more proximate mainland species ( M. tenaki ) that ranges from Cape Reinga to North Cape ( Seldon & Leschen 2011).

Distribution: New Zealand, North Island, Three Kings Islands (only).

Holotype: NZAC male labelled [card mounted]. Type [round label with red border glued to card] / Great Island Three Kings 1– 3.1.63 E.S. Gourlay [hw] / under large stones in forest Ca. 200’ [hw] / HOLOTYPE ♂ Mecodema regulus mihi [hw] / E.B. Britton det. 1964 [date hw] / NZAC 04011202 .

Paratypes: (see Seldon & Leschen 2011).

Material examined: 1♂, NEW ZEALAND TH Great Is. Tasman Valley Tasman Tk 7 Nov 2008 under rocks T Buckley R Leschen TH 020 34°09.763, 172°08.348 ( NZAC) 1, NEW ZEALAND TH Great is. Bayliss Tk along Bayliss Strm 8 Nov 2008 under rocks T Buckley R Leschen TH 023 34°09.732/172°08.612 ( NZAC) ; 1♀, NEW ZEALAND TH Great is. Bayliss Tk along Bayliss Strm 8 Nov 2008 under rocks T Buckley, R Leschen TH023 34°09.732, 172°08.612 ( 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 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 11. Detail of pronotum showing the taxonomic structures used in the species descriptions. PPC = posterior pronotum constriction; PS = pronotal setae; PAA = pronotum anterior angle; AE = anterior edge; PC = pronotal carina; ML = midline; PF= pronotal foveae; PPS = pronotum posterior sinuation; PE = posterior edge.

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 50. Mecodema regulus 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.