Mecodema pluto 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 : 92-94

Mecodema pluto Britton, 1949 .

Figures 12B and 47 .

Diagnosis: Distinguished from other Mecodema species by: 1, pronotum with 4–6 setae along pronotal carina ( curvidens species group). Differing from other curvidens group species by: 2, the presence of a distinctive raised ridge anterad vertexal groove; 3, the overall pronotal shape is ovate; 4, elytral interval 9 broad and shortened, i.e. not extended to humeral angle.

Description: Length 15.8–23 mm, pronotal width 4.5–5.6 mm, elytral width 5.1–6.9 mm. Colour of entire body matte to glossy black, coxae and legs may be dark red.

Head: Narrow and convex ( Fig. 14D ). Vertex smooth ( Fig. 47 ); vertexal groove shallow and narrow, defined entirely and very distinctive by raised posterior edge of frons; large supraorbital puncture bearing 3 setae; 2 welldefined supraorbital grooves; frons medially convex with a small and shallow depression each side of midline; frontoclypeal suture indistinct, tentorial pits ( Fig. 9 ) small; anterior area of clypeus with narrow grooves, 1 setose puncture each side bearing 2 setae ( Fig. 47 ). Labrum rounded, anterior edge outwardly curved with 2 proximate central setae, 2 setae each side evenly spaced. Mentum lobes squared ( Fig. 12G ), median process broad and short, sligthly angled upward (15°), moderately indentate ( Fig. 12B ); mentum setae present. Submentum sclerite constriction broad with 6–8 setae (2 setae spaced distantly laterally). Stipes with 2 basal setae. Gula pits small, suture defined, gula ( Fig. 8 ) flat with transverse lines. Gena with very fine lines forming an isodiametric pattern across entire area.

Prothorax: Prothoracic carina narrow the entire length, slightly crenulated with 4–6 setae each side ( Fig. 47 ), extended to anterior angle; posterior lateral sinuation ( Fig. 11 ) evidently carinate, parallel, indistinctly crenulated; prontum narrow and moderately deflected, overall shape ovate ( Fig. 47 ); midline impressed, anterior medial and posterior medial diamond-shaped impressions present; disc may have very fine, transverse wrinkles laterally; pronotal foveae deep and narrow; anterior edge distinctly inwardly curved, posterior edge inwardly curved medially. Prosternum concave without microsculpture; proepisternum without microsculpture. Procoxal setae absent; protibia distally expanded and shovel-like ( Fig. 10B ).

Elytra: Narrow and moderately deflected; humeral angle anteriorly convergent ( Fig. 6A ); basal margin moderately curved and steeply bevelled (almost vertical) to base, intervals 6–8 truncated by raised carina laterally proximate to humerus, interval 1 extended to margin; lateral carina ( Fig. 1 ) narrow the entire length, extended to humeral angle; humerus with 2 setose punctures proximate to angle; suture impressed, but no more so than striae; all striae with small, regularly distributed, asetose punctures (in some specimens striae 1–4 punctures may be obsolescent); intervals 1–4 weakly convex, intervals 5–9 moderately convex with interval 9 broadened and shortened, not extended to humeral angle; interval microsculpture present as transverse lines; 7 th strial setal pattern with 1–2 setose punctures in anterior ½, 3–5 setose punctures in posterior ½ ( Fig. 47 ), setose punctures large.

Ventral surface: Mesepisternum and metepisternum with rugose wrinkles present; setose punctures present on mesocoxa (2) and metacoxa absent. All abdominal ventrites ( Fig. 2 ) finely lineate laterally; ventrites 3–5 without setose punctures; ventrite 6 setae present: ♂ with 2–3 setose punctures each side, proximate junction of straight apical edge and curve anterad, ♀ with 2 broad setose punctures relatively proximate bluntly rounded apex; ventrites without foveae. Anterior metaventrite process a bluntly rounded triangle with a well-defined, apically broadened to laterally narrowed carina.

Male genitalia: Apical portion of penis lobe asymmetrically rounded with a moderate deflection to right of vertical axis (VV) ( Fig. 15B ); apex of penis lobe symmetrically curved upward, dorsal curve flattened ( Fig. 47 PL); shaft of penis lobe narrowed apically but gradually broadened basally, curve to right absent (VV); overall length of penis lobe slightly curved ventrally (LV) ( Fig. 16A ). 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 sparse (1–25%); size of left setose flange small; size of right setose flange large. Left paramere basal lobe ovate ( Fig. 47 LP), short slope to arm; arm short and broad, terminal lobe indistinct but abruptly narrowed at terminus, apical tuft of long setae, medium-lengthed setae extended along apical ¾ of ventral edge ( Fig. 47 LP); ventral edge slightly curved. Right paramere narrowly triangular with an apical tuft of long setae, medium-lengthed setae extended along apical ¾ of ventral edge ( Fig. 47 RP).

Female genitalia: Basal gonocoxite 1 short and narrow, flattened apically, ventral surface smooth, internal dorso-lateral carina with 2 setae. Gonocoxite 2 ( Fig. 5 ) narrowly elongated, a bluntly rounded triangle, apically reflexed. Ramus short and broad.

Comments: Mecodema pluto was described by Britton (1949) from one badly damaged specimen, and even though the type locality is Mt Te Aroha, specimens are more easily collected in Kauaeranga Valley, Coromandel.

Distribution: New Zealand, North Island, southern Coromandel Range and northern Kaimai Range.

Holotype: BMNH labelled [card mounted]. Te Aroha Trig. Stn. 1001. [hw] Type [round label with red border] glued on card / 1200 [light blue label glued on card] / Te Aroha N. Zealand. H. Swale. 1913–117. [broad pink line below collector name] / HOLOTYPE Mecodema pluto n. sp. [hw] E. B. Britton det. 6.11.1945 [hw].

Paratypes: (see Seldon & Leschen 2011).

Material examined: 1♀, NEW ZEALAND CL Kennedy Block Sce Res 28.XII.1993 – 2.I.1994 Larivière. Larochelle / Moist for (tree fern-nikau-Phyllocladus) Stony soil. Pit traps ( NZAC) ; 2♂, NEW ZEALAND, CL , Coromandel Range , Kauaeranga Valley, Trestle View camp PTs 19 Oct–5 Nov 2010, D.S. Seldon DSS043 / CAR 074 ( AMNZ) ; 1♂, NEW ZEALAND BP Te Aroha Forest Park, Tui Ridge Summit Track , S37°31.4718, E175°43.9158, A. Seago / U.C. Berkeley EMEC 205,853 / CAR 055 ( UCBC) ; 1♀, NEW ZEALAND CL Maumaupaki Track 800m 8.XI–6.XII.1993 Larivière. Larochelle / Moist for. (tawa-supplejack- Coprosma ) Rich litter Pit traps ( 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 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 47. Mecodema pluto 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.