Trigonaptus, Fedorenko, 2020

Fedorenko, D. N., 2020, New taxa of Pterostichini (Coleoptera: Carabidae) from Vietnam, Russian Entomological Journal 29 (1), pp. 38-52 : 48-50

Trigonaptus Fedorenko, gen.n.

Figs 31–32 , 39–52.

Type species: Trigonaptus inaequalis Fedorenko, sp.n.

DIAGNOSIS. The new genus includes two Trigonotoma -like species recognizable in the combination of very long antennal scape; lateral lobes of mentum pointed and much produced beyond median tooth; labrum with setae equidistant and basal membrane not or slightly exposed due to clypeus truncate to gently sinuate apically; terminal labial palpomere triangular; metepisterna short following apterous condition; antennal pedicel with ventral seta. For details see also ‘Comments’ below.

DESCRIPTION. Body ( Figs 31–32 ) apterous, mediumto large-sized.

Head bisetose on each side, subtriangular, large and long, with neck incrassate; neck constriction missing or indistinct. Eyes small, longer than genae. Clypeus bisetose, transversely hexagonal, with apex truncate or slightly V-shaped, frontoclypeal suture fine, transversely straight. Frontal sulci deep, short to long. Antennae geniculate, short, reaching the level of basal 1/4–2/5 pronotum; scape very long, as long as antennomeres 2 to 5 combined, distinctly surpassing eye behind, with dorsal seta; pedicel with ventral seta.

Labrum obtrapezoidal, sexsetose; apical sinuation even or V-shaped. Mandibular scrobe with a deep longitudinal median sulcus. Maxillary stipes bisetose. Mentum short, apically beaded; lateral lobes slightly pointed and projecting far beyond median tooth; the tooth short and wide, more or less bifid, with a seta at each angle\tooth and small yet deep labial pits behind. Submentum bisetose, very short, costate medially or nearly throughout; gula wide, trapezoidal, almost reaching sides of head basally. Ligula long and wide, bisetose apically, paraglossae membranous, dorsal, barely longer than ligula. Terminal maxillary palpomere fusiform; terminal labial palpomere triangular, 1/2–3/5 as wide at apex as long at inner margin; penultimate labial palpomere bisetose.

Pronotum subcordate, without basal bead; apical bead obliterate except at apical angles. Reflexed lateral margin rather narrow, costate or almost so; lateral groove obliterate in basal quarter; basal foveae smooth, flat and deep between basal sulci, outer sulcus separated by a fold from lateral groove. Anterolateral seta in lateral groove, posterolateral seta close to basal angle.

Elytra connate, elliptic, each with internal plica and a distinct preapical sinuation. Humeri distinct. Basal ridge inwardly reaching stria 2 or 3, humeral angle obtuse or very so. Striae deep punctate; parascutellar striole missing or vestigial. Chetotaxy: parascutellar seta in interval 2 near stria 2, discal setae missing, two apical setae in stria 7; USS continuous, consisting of 18–24 US.

Ventral side coarsely punctate along sides, including propleura, mes- and metepisterna and abdominal sternites II– VI. Prosternal process without marginal bead. Mesoventrite toothed or with a fine ridge in front of each mesocoxa. Metepisternum as long as wide or barely transverse. Abdominal sternites VI –VII deeply sulcate along bases; sternite VII bisetose in male, quadrisetose in female.

Legs, including setation, as in Trigonotoma Dejean, 1828 : profemur posteriorly bisetose (basal seta missing), protibia slightly dilated apicad, apically with two posterolateral spinules and one posterior spinule. Mesofemur with two subequally spaced anteroventral setae and two anterodorsal setae in apical two fifths; mesotibia with three outer setae, distal seta inserted closer to anterior ridge. Metacoxa bisetose laterally (inner seta missing), metatrochanter rounded apically, less than half as long as metafemur, asetose; metafemur with basal anteroventral seta; metatibia with 1–3 outer setae. Tarsomeres 1–4 each with one pair of latero-apical setae, tarsomeres 1–2 each with one pair of dorso-apical setae; tarsomere 5 with three pairs of ventral setae. Meso- and metatarsi anteriorly (outwardly) with a more or less distinct lateroventral sulcus bearing a row of setae running on tarsomeres 1–2 or 1–3; either lateral carina and laterodorsal sulcus missing or the latter indistinct. Tarsomeres 1–3 dilated and biseriately squamose in male.

Aedeagus (Figs 39–52): median lobe more or less curved in lateral view, right paramere short. Internal sac divided into two isolated parts, internal sac proper and a more or less developed accessory proximal bulb.

NAME. Masculine, an abbreviated combination of the generic names Trigonotoma and Pareuryaptus , referring to the similarity of the new genus to the two taxa.

DISTRIBUTION. The member species of the genus are only known from single locality each, either a mountain in southern Vietnam or a small plateau in Central Vietnam.

HABITS AND HABITATS. Occurs in monsoon forests.

COMMENTS. The ‘Trigonotomi’ group includes one Papuan genus, Leiolesticus Roux et al., 2016 and six Oriental ones, Lesticus Dejean, 1828 ; Trigonotoma Dejean, 1828 ; Euryaptus Bates, 1892 ; Nesites Andrewes, 1939 (= Aloma Andrewes, 1931 ); Pareuryaptus Dubault et al. ; 2008; and Trigonaptus gen.n. All these taxa ( Nesites , Euryaptus and Leiolesticus not seen) share significant, mostly derived, characters as follows: body medium to large-sized and glabrous; abdominal sternites sulcate basally; gula wide to very wide basally; mandibles rather large, with apex narrow, strongly pointed and incurved; legs, including protibiae, fairly slender, with rather weak spinuous armature; terminal labial palpomere broadened apicad, either subtriangular in both sexes or securiform in male; metacoxa bisetose or unisetose laterally; metatrochanter asetose; tarsomere 5 setose ventrally; protarsomeres 1–3 dilated and biseriately squamose ventrally in male. For other features see Roux et al. [2016].

The new genus is distinctive from the other taxa of ‘Trigonotomi’ in having a peculiar character combination (Table). To trace probable relationships within this group, we leave below autapomorphies of Trigonaptus gen.n. (72) and Pareuryaptus (111121) out of consideration. Character 141 is also of little value for the purpose because it is highly functional and has been developed many times within Carabidae in course of evolution.

Characters 10 – 40 have been retained by Lesticus (and probably also Leiolesticus ) only, which invites the basalmost position of the genus within the ‘Trigonotomi’, and multiple symplesiomorphies (50 – 100140) also argue in favour of this hypothesis. Accordingly, synapomorphies 11 – 41+2 support monophyly of the other genera, character 42 being probable autapomorphy of Trigonotoma . The genus otherwise is the most primitive within this lineage, since plesiotypic characters are as many as apotypic ones (6090100517181). Euryaptus , Pareuryaptus and Nesites share apotypic characters 516191101 and Nesites is distinctive within this trio in the combination of plesiotypic character 80 and apotypic 141. Euryaptus and Pareuryaptus seem to be closely related because their distribution patterns are vicariant, western or eastern, respectively, and character 70 / 71 only serve for discrimination between the two taxa; this difference is also not deep because the antennal scape varies from species to species of Pareuryaptus considerably in length. This suggests also that the short scape may have evolved into a long one more than one time in the group considered.

The characters Trigonaptus gen.n. share with Trigonotoma / Nesites / Pareuryaptus are 7190100131 / 617180141 / 6171, respectively. Except for character 14, the characters shared are four for the first couple, three for the second, and two for the third. This may suggest that the new genus is closer to Nesites or Trigonotoma , but this hypothesis much depends on whether some of the characters 6191101131 and also 71 have been developed in parallel or not. Some plesiotypic characters (508090100) point to a considerable primitiveness of the new genus.

Because characters of the aedeagus and its internal sac vary within Trigonaptus gen.n. and Trigonotoma considerably, they only contribute a little to understanding the relationships between Trigonotoma , Pareuryaptus and Trigonaptus gen.n. Those genitalic features may be useful for the purpose nevertheless, that define the main two aedeagus types, the Trigonotoma - type and the Pareuryaptus - type. The former is generally defined by a simple internal sac, combined with the apex of the median lobe being large, obtrapezoidal, conspicuously curved to the right, with a dorsal carina. The Pareuryaptus - type includes the internal sac double, with an accessory proximal bulb, and the apex of the median lobe symmetric, widely rounded, very short to indistinct, without dorsal carina. Trigonaptus gen.n. and some species of Trigonotoma , e.g., T. perraudieri Bates, 1889 match this aedeagus-type well, except that the median lobe has a large apex.

Characters (states: 0, plesiotypic; 1–2, apotypic; 1´, homoplasy):

1. gula: (0) moderately wide, with its sides barely diverging and base only a third as wide as moderately wide neck — (1) brodeaned much basad, with sides strongly diverging, only slightly narrower at base than incrassate neck;

2. profemur: posteriorly (0) trisetose — (1) bisetose owing to basal seta lost;

3. antennae: (0) long, distinctly surpassing elytral base — (1) short, not surpassing basal 1/4 pronotum;

4. mentum: (0) moderately transverse, epilobes well-developed, as very obtuse median tooth at inner margin of lateral lobes; these slightly surpassing mentum tooth in front — (1) transverse, epilobes strongly reduced in size, modified into a tooth-like dilation of apical bead just outside median tooth, lateral lobes more or less pointed and much surpassing median tooth anteriorly — (2) very transverse; lateral lobes truncate and very short, on a level with median tooth;

5. mentum tooth: (0) more or less bifid, with angles distinct and apical margin slightly concave — (1) subtruncate to much rounded, with angles very blunt to missing;

6. elytron parascutellar striole: (0) well-developed — (1) vestigial to totally reduced (this character state actually means quite otherwise, i.e., stria 1 anteriorly obliterate and directly extended into a well-developed parascutellar striole);

7. antenna: scape (0) short, shorter than antennomeres 2 and 3 combined — (1) very long, not or barely surpassing mid-eye level, mostly shorter than antennomeres 2 to 5 combined — (2) extremely long, distinctly surpassing eyes behind, as long as antennomeres 2 to 5 combined;

8. terminal labial palpomere: (0) subtriangular — (1) securiform in male;

9. labral setae: (0) subequally spaced — (1) lateral setae distant far from inner four;

10. abdominal sternite VII: (0) quadrisetose in female — (1) bisetose in both sexes;

11. metacoxa: (0) laterally bisetose, with inner seta only missing — (1) unisetose, posterolateral seta lost;

12. antennal pedicel: (0) with ventral seta — (1) glabrous;

13. meso- and metatarsi: (0) without anterolateral setae — (1) with a row of anterolateral (outer) setae;

14. body: (0) macropterous, metepisterna distinctly longer than wide — (1) apterous, metepisterna short.

Based on these facts and suggestions, the relationships of the genera considered is likely to be Lesticus + ( Trigonotoma + ( Trigonaptus gen.n. + ( Nesites + ( Pareuryaptus + Euryaptus )))).

Figures

Figs 30–32. Dorsal habitus, holotypes: 30 — Pterostichus (Vietosteropus) kuznetsovi sp.n.; 31 — Trigonaptus inaequalis gen. et sp.n.; 32 — T. longiscapus sp.n. Рис. 30–32. Габитус дорЗально, голотипы: 30 — Pterostichus (Vietosteropus) kuznetsovi sp.n.; 31 — Trigonaptus inaequalis gen. et sp.n.; 32 — T. longiscapus sp.n.