Mecodema antarctica Castelnau, 1867

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 : 22-25

Mecodema antarctica Castelnau, 1867 , comb. n.

Figure 17 .

Brullea antarctica Castelnau, 1867 .

Diagnosis: Mecodema antarctica is distinguishable from all other North Island Mecodema species by having: 1, greatly expanded protibia and mesotibia; 2, ventrites with numerous setose punctured; 3, pronotum and elytra truncated; all adaptations for a psammaphilous lifestyle.

Description: Length 20–28 mm, pronotal width 6.5–8.3 mm, elytral width 7.7–9.9 mm. Colour of entire body deep reddish-bronze to glossy black.

Head: Narrow and convex laterally ( Fig. 14D ). Vertex smooth, some very fine transverse wrinkles may be present laterally ( Fig. 17 ); vertexal groove defined by broad and shallow depressions laterally, otherwise smooth; small supraorbital punctures bearing 2 setae; a single shallow supraorbital groove in front of eye, a few very small wrinkles mesad eye may be present; frons smooth; frontoclypeal suture a very narrow groove, very small tentorial pits; anterior area of clypeus with a very shallow depression each side of midline; clypeus with 1 setose puncture laterally, bearing a single seta. Labrum rectangular, laterally rounded with anterior edge straight to slightly outwardly curved with 2 proximate central setae, 2 setae each side evenly spaced. Mentum lobes squared, median process very short and broad, upward angle absent, deeply indentate ( Fig. 12A ); setose punctures variably present or absent. Submentum sclerite constriction narrow with 6 setose punctures evenly spaced. Stipes with 2 basal setae. Gula pits small in deep recess, suture very narrow (difficult to define on darker specimens), gula flat and smooth. Gena with a very fine isodiametric pattern laterally.

Prothorax: Prothoracic carina narrow the entire length, smooth to weakly crenulated with 3–4 setae each side ( Fig. 17 ), extended beyond anterior angle; posterior lateral sinuation indistinctly carinate, parallel; pronotum broad and rounded laterally, edges angled inward laterally to head forming overall orbicular shape (truncated); midline ( Fig. 11 ) well-defined, medial impressions absent, disc with fine transverse wrinkles laterally ( Fig. 17 ); pronotal foveae broad and very shallow; anterior edge slightly inwardly curved, posterior edge curved postero-laterally forming a moderate curve medially. Prosternum flat and smooth; proepisternum without microsculpture; Procoxal ( Fig. 2 ) setae absent; protibia greatly distally expanded and shovel-like ( Fig. 10A ), apical spur greatly dilated; profemur shortened and broad.

Elytra: Broad, rounded and truncated, almost ovate in shape, distinctly deflected laterally; humeral angle anteriorly convergent ( Fig. 6A ); basal margin slightly curved and bevelled to base (intervals and striae truncated at margin); lateral carina very narrow the entire length, extended to humeral angle, lateral carina setae in deep punctures (clearly visible); humerus with 1 anterior setose puncture, 2 evenly spaced posterad (some variation in number of setae present); suture defined by interval 1 extended to scutellum; striae 1–4 with obsolescent punctures, striae 5–6 punctures slightly increased in size, but indistinctly impressed, striae 7–8 with larger pits, (may be starshaped); intervals 1–3 weakly convex, increasingly convex laterally (intervals 4–9); interval microsculpture absent; 7 th strial setal pattern with 1–2 setose punctures in anterior ½, 3–4 setose punctures in posterior ½, all setose punctures in broad pits.

Ventral surface: Mesepisternum and metepisternum without microsculpture; setose punctures of mesocoxae (1) and metacoxae present (2), large shallow foveae present on metacoxae; mesofemur and metafemur shortened and broad, mesotibia shortened and apical spur dilated; metatibia shortened, greatly curved outwardly, apical spur dilated. Abdominal ventrites 1–5 smooth; ventrite 3 with 2 setose punctures in shallow depression each side (not laterally), ventrite 4 with 5–9 setose punctures in shallow depressions each side (midline to sides with gap), ventrite 5 with 9–10 setose punctures in shallow depression each side; ventrite 6 setae present: ♂ with 6–7 short grooves along straight apical edge, ♀ with 3–6 setae on each side along a rounded apical edge; ventrites foveate laterally. Anterior metaventrite process rounded at apex and deeply concave and without carina.

Male genitalia: Apical portion of penis lobe symmetrically rounded ( Fig. 17 PL), evenly curved dorsally without a deflection to the right of vertical axis (VV); shaft of penis lobe broadened toward base (midpoint broader than base), moderately curved entire length (VV), overall length of penis lobe shortened and straight (LV) ( Fig. 17 PL). 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 is sparse (1–25%); left setose flange is small, right setose flange is large. Left paramere basal lobe rectangular with slight anterior hump, short slope forming a very broad arm that narrows gradually to a large terminal lobe ( Fig. 17 LP), arm and lobe inwardly curved across penis lobe; terminal lobe with a tuft of long setae, short and sparse setae extended apically along ¾ of length; ventral edge of basal lobe straight ( Fig. 17 LP). Right paramere curved, narrowly triangular (¾ width of left paramere), apex with tuft of long setae, short and sparse setae extended along apical ¾ along ventral edge ( Fig. 17 RP), inwardly curved toward penis lobe.

Female genitalia: Basal gonocoxite 1 ( Fig. 5 ) short and narrow, ventral surface glaborous, sensillar pits present; inner surface grooved, internal dorso-lateral carina with setae absent. Gonocoxite 2 paddle-like, apex bent outward, with sensillar pits present. Ramus long (over ½ length of gonocoxite 1) and broad.

Comments: The greatly distally expanded protibia and mesotibia are probably used for burrowing into sand. The shortened length of the abdomen and the increased number setae on the ventrites are presumed to reduce wear on the dragging abdomen. All are characters associated with species adapted to dwelling on sand dune systems.

Distribution: New Zealand, North Island: mostly west coast (but some east coast areas) sand dune systems from Northland, Auckland, Waikato, Gisborne, Taranaki, Wanganui, Wellington; South Island: Nelson, Westland.

Holotype: MCNG specimen labelled. Auckland Coll. Castelnau [hw, black square border] / Brullea antarctica Cast. [hw] / Typus [red font, red square border] / antarctica Cast. [hw, black square border] / HOLOTYPUS Brullea antarctica Castelnau, 1867 [hw, red label] / Museo Civico di Genova.

Material examined: 1♂, NEW ZEALAND ND Te Paki Res, Te Paki Stream 50m, 15.II.1995 Larivière, Larochelle / Sand-dunes: open, bare yellow soil ; 1♀, NEW ZEALAND AK Helensville 14.II–18.III.1993 A. Larochelle. M-C Larivière / sandy vacant lot pittraps; 1, Waikawa Beach, S. of Levin, 20.X.96, J.I.Townsend [hw] / J.I. Townsend Collection / NZAC04006420 ; 1♀, In sand dunes Waitarere Beach 13.1.80 J.I.Townsend [hw] / J.I. Townsend Collection / NZAC04006409 ; 1♂, NEW ZEALAND Te Werahi Beach sand dune NZMS 260 MO2 957499 dead, Aug 1997 I.A.N. Stringer / J.I. Collection / NZAC04006392 .

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 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 17. Mecodema antarctica 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.