Trechus nanulus, Schmidt & Faille, 2018

Schmidt, Joachim & Faille, Arnaud, 2018, Revision of Trechus Clairville, 1806 of the Bale Mountains and adjacent volcanos, Ethiopia (Coleoptera, Carabidae, Trechini), European Journal of Taxonomy 446, pp. 1-82: 13-15

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Trechus nanulus

sp. nov.

Trechus nanulus   sp. nov.

Figs 4 View Figs 1–4 , 8 View Figs 5–8 , 12 View Figs 9–12 , 42–43 View Figs 37–56


Habitus and male genital characters very similar to T. gypaeti   and T. minitrechus   sp. nov. from Mt Enkuolo, but slightly smaller, colour of body distinctly darker brown and shinier with elytra iridescent, pronotum and elytra with meshes of microsculpture less deeply engraved, eyes larger and more protruded, pronotum more transverse, elytra broader and shorter with preapical seta developed, and aedeagal median lobe stouter. Trechus nanulus   sp. nov. is also very similar to T. rira   sp. nov. but readily distinguished by larger eyes and stouter aedeagal median lobe (see below for details). Compared to all other Trechus   species of the Ethiopian fauna, the new species differs by the combination of the following characters: body length below 2.5 mm, only one protarsomere of male dilated, elytral striae indistinctly impressed on disc; aedeagal median lobe apex simply tapered.


The specific epithet refers to the very small body length of the species and particularly to the fact that it represents the smallest Trechus   species known from Ethiopia.

Material examined


ETHIOPIA: ³, Oromia, S slope Bale Mts below Rira , alt. 2380 m, 06°43′17″ N, 39°43′14″ E, Dec. 2006 ( CSCHM, registration number ZSM _COL_2018_004).



ETHIOPIA: 3 ³³, 3 ♀♀, same data as for holotype ( CAF, CSCHM). 7 ³³, 6 ♀♀, Bale Mts, Harenna Forest, E Rira, alt. 2690 m, 06°43′25″ N, 39°45′25″ E, Feb. 2007 ( CAF, CSCHM); 37 ³³, 29 ♀♀, same data as for preceding but 13 Dec. 2017 ( NHMUK, CAF, CDH, CSCHM, MNHN, ZMAA); 7 ³³, 8 ♀♀, Harenna Forest, W Rira, alt. 3000 m, 06°45′57″ N, 39°41′47″ E, 14 Dec. 2017 ( CSCHM).


BODY LENGTH. 2.2–2.4 mm (Ø = 2.29 mm, n = 20).

PROPORTIONS (n = 10): PW /HW = 1.35–1.42 (Ø = 1.38); PW / PL = 1.50–1.60 (Ø = 1.56); PW /PBW = 1.22–1.30 (Ø = 1.25); EW/ PW = 1.41–1.51 (Ø = 1.46); EL/EW = 1.24–1.31 (Ø = 1.28).

COLOUR. Head, pronotum and elytra dark brown, markedly shiny, elytra slightly iridescent. Clypeus, labrum, palpi, antennal base and legs yellowish; antennae distally darkened beginning from third antennomere.

MICROSCULPTURE. Same in males and females. Head with comparatively large, almost isodiametric meshes on disc and supraorbital area, and smaller meshes on clypeus. Pronotum and elytra with slightly engraved narrow transverse meshes, which are narrower on elytra than on pronotum.

HEAD. Comparatively robust. Mandibles short. Labrum with apical margin widely emarginated. Eyes moderately small, distinctly convexly protruded. Tempora convex, markedly wrinkled to the neck, 0.9 times as long as eyes, very finely and sparsely pubescent. Frons and supraorbital area strongly convex, with supraorbital furrows almost uniformly bent on disc, deep throughout. Antennae short, proportions of the first four antennomeres as follows: 1/1/0.9/0.7; antennomeres 7–9 only slightly longer than broad.

PROTHORAX. Pronotum large, markedly transverse, broadest portion slightly before middle, base as wide as apical margin. Disc markedly convex. Anterior margin slightly concave with anterior angles slightly protruded. Sides almost evenly rounded throughout. Laterobasal angles very obtuse, blunt at apex. Marginal gutter very narrow, not widened near laterobasal angles. Base straight in middle, distinctly bent anteriorly at outer quarter. Median longitudinal impression fine but distinct, not deepened near base, disappearing at apex; anterior transverse impression very shallow, smooth; posterior transverse impression shallow, laterobasal foveae very small, notch-like, smooth. Pronotum with laterobasal setae present.

PTEROTHORAX. Elytra convex on disc, in dorsal view markedly short and broad, broadest in mid-length, with shoulders fully rounded; broadly rounded at apex. Striae impunctate, parascutellar stria and first stria absent, latter sometimes finely impressed near apex, striae 2–5 indistinct but present, striae 6–7 usually absent, stria 8 impressed only at levels of the middle and subapical groups of the marginal umbilicate pores. All intervals flat. Recurrent preapical stria deep, curved in front, directed to the fifth stria. Third stria with two setiferous dorsal pores, the anterior one slightly behind the anterior elytral quarter, the posterior one slightly behind middle (except in one specimen without posterior discal seta!), and with preapical seta which is situated at the apical anastomosis of second and third striae slightly closer to the elytral apex than to the suture. Number and positions of the setae of the marginal umbilicate series as in Trechus   s. str. ( Fig. 12 View Figs 9–12 ).

LEGS. Short and comparatively thin; protibia slightly dilated towards apex, hardly bowed, finely but distinctly grooved on external surface. Only one basal protarsomere of male dilated.

MALE GENITALIA. EL / AL = 4.00–4.28 (Ø = 4.13, n = 6). Aedeagal median lobe small and stout, in lateral view with ventral margin slightly bent near base and apex, straight in middle; apical lamella moderately

short with apex simply tapered; basal bulb moderately large, sagittal aileron average. Endophallus with copulatory piece bag-like, triangular in lateral view, arcuate towards apex, very slightly sclerotized.


Known only from Harenna Forest on the southern slope of the Bale Mts, below Rira village, at altitudes of 2380–2690 m.


Department of Botany, Swedish Museum of Natural History


Nanjing University


Royal Botanic Garden Edinburgh


Bavarian State Collection of Zoology


Natural History Museum, London


Museum National d'Histoire Naturelle


Naturhistorisches Museum Wien