Mecodema perexiguus, 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 : 90-92

Mecodema perexiguus sp. n.

Figure 46 .

Diagnosis: This is the smallest species of Mecodema found on the North Island and is distinguished from other Mecodema species by: 1, the overall body width being narrow (4.9–5.2 mm); 2, the pronotal carina with 4 setae each side; 3, elytral striae with very small, asetose punctures that are indistinct along striae 1–4.

Description: Length 16–16.7 mm, pronotal width 4.3–4.5 mm, elytral width 4.9–5.2 mm. Colour of entire body matte to glossy black, coxae and femur dark red.

Head: Narrow and convex ( Fig. 14D ). Vertex smooth ( Fig. 46 ); vertexal groove shallow and broad laterally; small supraorbital puncture bearing 2–3 setae; 2–3 indistinct supraorbital grooves; frons convex medially with a very shallow and small depression each side; frontoclypeal suture well-defined the entire length, tentorial pits ( Fig. 9 ) indistinct; anterior area of clypeus with 3 indistinct grooves, 1 setose puncture each side bearing 1 seta. Labrum rounded, anterior edge weakly emarginated with 2 proximate central setae, 2 setae each side evenly spaced. Mentum lobes squared ( Fig. 12G ), median process long and narrow, upward angle absent, slightly indentate ( Fig. 12C ), mentum setae present. Submentum sclerite constriction narrow, folded with 3 setae clustered very wide laterally (1 seta each side mesad of other 2). Stipes with 2 basal setae. Gula pits ( Fig. 8 ) small, suture defined, gula flat with transverse lines. Gena with very fine isodiametric pattern across entire area.

Prothorax: Prothoracic carina narrow the entire length, smooth with 4 setae each side ( Fig. 46 ), extended beyond anterior angle; posterior sinuation indistinctly carinate, slightly angled inward; pronotum narrow and moderately deflected especially laterally, overall shape squared ( Fig. 46 ); midline indistinct, anterior medial diamond-shaped impression may be present, disc with very sparse, indistinct lines laterally; pronotal foveae narrow and shallow; anterior and posterior edges relatively straight. Prosternum flat with fine transverse lines; proepisternum without microsculpture. Procoxal setae absent; protibia distally expanded and shovel-like ( Fig. 10B ).

Elytra: Narrow and flattened, moderately deflected laterally; humeral angle evenly convex ( Fig. 6B ); basal margin moderately curved and gently sloped to base, interval 1 extended to margin; lateral carina narrow the entire length, extended to humeral angle; humerus with 1 setose puncture ( Fig. 46 ); suture indistinct (less impressed than striae); all striae with very small, regularly spaced, asetose punctures (striae 1–4 punctures obsolescent); intervals 1–4 flat, intervals 5–9 weakly convex; interval microsculpture present as very fine lines; 7 th strial setal pattern with 1–2 setose punctures in anterior ½, 3–4 setose punctures in posterior ½ ( Fig. 46 ), setose punctures large.

Ventral surface: Mesepisternum lineate and obsolescently micropunctate; metepisternum with scattered, obsolescent punctures; setose puncture present on mesocoxa (1), absent on metacoxa. Abdominal ventrites ( Fig. 2 ) 1–6 without microsculpture; ventrites 3–5 without setose punctures; ventrite 6 setae present: ♂ with 2 setose punctures each side, apical edge a gently rounded curve, ♀ with 2 setose punctures each side, apical edge a pointed curve; ventrites without foveae. Anterior metaventrite process ( Fig. 2 ) a short rounded triangle with a broad carina the entire length.

Male genitalia: Apical portion of penis lobe symmetrically rounded with apex squared, moderate deflection to right of vertical axis (VV) ( Fig. 15B ); ventral edge of penis lobe curved slightly to left (VV), penis lobe shaft narrow the entire length, apical portion slightly broadened ( Fig. 46 PL), overall length of penis lobe straight (LV). 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 narrowly rectangular without dorsal hump, moderately sloped (45°) to arm; arm long and narrow, gradually narrowed to terminus; apical tuft of very long setae, medium-lengthed setae continued along apical ½ of ventral edge ( Fig. 46 LP); ventral edge of basal lobe straight. Right paramere long and narrowly triangular, long arm with long setae extended along apical ½ of ventral edge ( Fig. 46 RP); apical portion distinctly inwardly curved across penis lobe.

Female genitalia: Basal gonocoxite 1 ( Fig. 5 ) short and broad, internal dorso-lateral carina without setae, ventral surface with a few shallow wrinkles. Gonocoxite 2 an elongated, narrow triangle, slightly broadened at base than rounded apex. Ramus long and narrow, rounded apically.

Comments: Mecodema perexiguus is found in coastal forests near Cape Runaway and it is currently not known how far this species’ range extends to the north or south.

Distribution: New Zealand, North Island, Bay of Plenty, East Cape.

Holotype: NZAC male labelled. NEW ZEALAND, BP Rereauira 20.XI.1992 A. Larochelle / Nothofagus forest: under rotten log / Rereauira Stream nr Cape Runaway / HOLOTYPE Mecodema perexiguus n. sp. design. DS Seldon, TR Buckley 2018 [red label].

Paratypes: 1♂, NEW ZEALAND, BP , Rereauira Swamp 9 Mar–25 Apr 1993 J.S. Dugdale / Pit trap ( NZAC) ; 2♀, NEW ZEALAND, BP Te Koau, bottom Track, Plateau 15 Mar 1993 J.S. Dugdale / under log and in gill fungus ( NZAC); 1, NEW ZEALAND BP Te Rereauira NZMS260 Y14 584906 9.iii.1993 J.M. Marris / underlog in Nothofagus truncata forest / EAST CAPE INSECT SURVEY 1992 / 3 / LUNZ00003000 .

Etymology: Perexiguus means very small, and this species is the smallest in terms of both body length and width for all described Mecodema species found in the North Island.

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 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 46. Mecodema perexiguus 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.