Pachytrechodes brevis Belousov & Nyundo, sp. n.
Creators: name: Belousov, Igor A.
name: Nyundo, Bruno A.
Publisher: name: Zenodo
Year: 2013
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Insecta
Coleoptera
Carabidae
Pachytrechodes
Pachytrechodes brevis

description: Pachytrechodes brevis Belousov & Nyundo, sp. n.
Type material: Holotype: TANZANIA: 1(1)3, “ Tanzania, Udzungwa Mts Nat. Park; forest floor, 1500 m asl; E36º52´00´´ S7º45´30´´; 03.viii.1999 Coll. B.A. Nyundo; searching on ground, daytime; B.A. Nyundo Expedition (1998–2001)”(ZMUN). Paratypes: TANZANIA: 10(2)3, 14Ƥ, collected with the holotype (UDSM, ZISP, ZMUN); 1(1)3, 17Ƥ, same data but 4.viii.1999 Coll. Hashim Rashid (cBK, ZISP, ZMUN); 7(5)3, same data but 5.viii.1999 (cBK, UDSM; ZISP, ZMUN); 2Ƥ, same data but 19.iv.1999 Coll. Hezron Mwasomola (UDSM). 20 specimens measured.
Description. Very small-sized apterous species. Body length 2.02–2.18 mm. Body robust and briefly ovate (Fig. 1), weakly convex, with fairly long legs and antennae. Dorsal side unicolorous reddish brown to dark brown, with paler brown yellowish legs. First antennomere yellowish, antennomeres 2–7 more or less distinctly obscured, distal antennomeres beginning with 8–9 becoming gradually paler. Head and pronotum occasionally darker than elytra.
Head rather small, much narrower than pronotum. Frontal furrows well and evenly impressed, arcuate, complete; frons convex. Eyes small, moderately protruding, more strongly in anterior third, slightly longer than tempora (eye length to temple length ratio 1.14–1.35), tempora strongly convex behind their mid-length, smooth, without any trace of pubescence. Labrum relatively narrow, its anterior margin deeply notched, bearing six setae, lateral lobes narrowly rounded. Mandibles (Fig. 2) rather short and thin, curved in apical quarter. Tooth on right mandible tridentate, with long base (i.e. proximal and distal denticles widely spaced). Last segment of maxillary palpi only little shorter than penultimate segment but much more narrow, subulate. Maxillary palpi completely glabrous. Penultimate segment of labial palpi quadrisetose. Mentum and submentum completely fused, without any trace of labial suture. Labial tooth simple, with anterior margin widely rounded to truncate. Four submental setae of which two are subangular. Glossum clearly notched at apex, with two large median setae and a few much smaller lateral setae. Paraglossae thin and long, faintly curved, protruding far beyond anterior margin of glossum. Two supraorbital setiferous pores on each side of head located on lines divergent posteriad. Anterior supraorbital setiferous pore strongly foveolate, posterior one without oblique fovea. Parietal transverse impression very shallow. Antennae rather long and thin, antennomeres 2 and 3 subequal in length, the latter being only marginally longer. Viewed from above, antennomere 2 nearly cylindrical, without distinct constriction in basal part.
Pronotum strongly transverse and convex, with basal lobe rather narrow and feebly produced; sides broadly rounded in anterior and middle part, nearly straight in posterior part, without distinct sinuation before hind angles. Lateral gutter very narrow throughout, only marginally widened near hind angles; lateral border complete, continued to basal lobe and more or less reduced only in most median part. Basal margin of pronotum weakly concave medially, obliquely emarginated laterally, most strongly sinuate near basal foveae, the latter extraordinarily small but deep, pore-like, attached to lateral border. Hind angles of pronotum obtusangular, blunt at apices or even completely rounded off. Front angles broadly rounded but detectable, weakly produced anteriad. Anterior margin of pronotum moderately and evenly concave. Apical transverse impression shallow, normally distinct laterally, reduced medially. Prebasal transverse impression very shallow, consisting of a median triangular depression and occasionally irregular lateral foveae. Median line finely engraved, normally developed only in median part. Discal foveae missing. Base of pronoum smooth, or, at most, with a few very shallow wrinkles. Anterior lateral seta of pronotum located markedly before mid-length of pronotum, slightly before its broadest point, posterior one in hind angles.
Elytra briefly ovate, more or less flattened on disk, steeply sloped laterally, with maximum width near midlength, sides broadly rounded at humeral area, nearly parallel in median part (though varying in this respect), broadly rounded at apex, with distinct preapical sinuation posteriorly. Lateral gutter evenly wide throughout its length, lateral margins moderately to weakly deflexed, without serration in humeral area. Basal border of elytra complete, with distinct sinuation at level of dorsal stria 4. Elytral striae rather well-impressed, at least five inner striae distinct in their median part, though becoming increasingly shallower and shorter toward sides, sixth stria distinguishable only fragmentary. First stria much more sharply engraved as compared to other striae, smooth, rectilinear, without distinct sinuation in anterior third while all other dorsal striae impressed more shallowly, waved and faintly punctured. Third stria angularly curved at anterior discal setiferous pore. Eighth stria distinct only in posterior half of elytra (only marginally extended anteriad beyond umbilicate pore 5) and some fragments may be distinguishable in humeral area. Interspaces flat. Parascutellar pore well developed, located anteriorly of basal border of elytra. Parascutellar striole sharply impressed, partially overlapped with basal portion of first discal stria. Apical striole clearly sinuate, moderately impressed posteriorly and very shallow anteriorly. Two discal setiferous pores in third stria (normally anterior one at level between umbilicate pores 3 and 4, and posterior one slightly before umbilicate pore 5) and one preapical pore located close to apex, in apical cross of third and second elytral striae at level slightly anteriorly of umbilicate pore 8. Both discal setiferous pores clearly foveolate, their setae very short and thin, shorter than parascutellar seta. Both apical pores present, located very closely to each other, anguloapical one being much less developed and located rather far from elytral suture. Umbilicate setiferous pores wellaggregated in longitudinal direction, but some pores (pores 3 and 4 weakly, pore 5 very strongly) translocated inward, onto disk of elytra.
Metathoracical wings reduced to small vestiges shorter than one fourth of elytra.
Legs rather thin and long, tibiae weakly curved. Protibiae without distinct pubescence on their anterior surface, sharply grooved exteriorly. Two basal segments in male protarsi dilated and dentate inward.
Ventral side of abdomen rather evenly pubescent except for lateral parts, two paramedian setae on visible abdominal ventrites 4–6. Two setae along posterior margin of anal ventrite in male and four setae in female. Posterior margin of anal ventrite concave in male, rounded in female.
TABLE 1. Morphometric characters of Pachytrechodes brevis, sp. n. The following abbreviations are used: a_pr —width of pronotum at apical margin; ante —length of antenna; b_pr —width of pronotum at basal margin; d_ i p —distance between level of i -th discal setiferous pore and basal border of elytra; eye —length of eye in dorsal view; h_ta —length of tarsus; h_ti —length of tibia; height —maximum height of body across elytra; l_2a —length of second antennal segment; l_3a —length of third antennal segment; l_el —length of elytra; l_pr —length of pronotum along median line; s_pr —distance between level of anterior lateral seta of pronotum and anterior margin of pronotum; tmpr —length of tempora; um_ i —distance from basal border of elytra to level of i th umbilicate pore; w_3a —width of third antennal segment; w_hd —maximum width of head across eyes; w_pr —maximum width of pronotum.
Microsculpture strongly reduced, making surface of body shining, only disc of pronotum with distinct microsculpture consisting of finely impressed transverse serrate lines.
Male genitalia (Figs. 3–4). Median lobe of aedeagus rather short and straight, bent only at basal portion; basal bulb bilobed. Dorsal wall not sclerotized. Endophallus armature consisting of one large heavily sclerotized plate gradually narrowing and pointed apically and a few less distinct plates in median part. Right and left parameres differ significantly in shape, left slightly triangular, right with distinctly attenuated apical half, more typical for most trechines, each paramere bearing four apical setae.
Sexual dimorphism. Male and female specimens are nearly identical in morphometric characters: males differ in having slightly larger eyes, longer antennae, smaller body size, and narrower head. Quantitative differences are indicated in Table 1.
Bionomics. The specimens were collected by searching in moist leaf litter on the forest floor of a montane tropical forest at an altitude of ca. 1500 m above sea level, Udzungwa Mountains National Park (formerly Mwanihana Forest Reserve). The vegetation of the area was dominated by tall trees (Dryptes sp., Vepris stolzii, Syzigium guineense, and Parinari excelsa). Tree ferns (Phoenix reclinata) were also common. The beetles were active from dusk to midnight under trees where there was fruit windfall. During the day they hid in the forest litter and could be collected by sifting the litter.
Comparative notes. The new species agrees well with the three other known congeners both in external and genitalic characters (Jeannel 1960; Uéno 1987). All four species of Pachytrechodes share the following character states: small and weakly produced eyes which are not significantly longer than convex tempora; small and robust body shape with relatively short legs and brief ovate elytra; microsculpture of dorsum more or less reduced, and inner elytral striae well impressed. The structure of the male genitalia is also very similar including both the shape of the aedeagus and the presence of the well-sclerotized copulatory pieces. In its small size (it is the smallest species of the genus) and a narrower pronotum, Pachytrechodes brevis sp. n. is more similar to P. basilewskyi Jeannel, 1960 and P. leleupi Uéno, 1987 than to P. u n c i n a t u s Uéno, 1987; however, P. b re vi s shares with the latter species the shape of the aedeagal median lobe with apex distinctly attenuated in lateral view and the presence of a large acuminate copulatory piece within the endophallus. Additionally, Pachytrechodes brevis differs from the other species of the genus in having clearly protruding eyes (versus very flat in P. uncinatus and P. basilewskyi), combined with the apex of the aedeagus attenuated in lateral view (versus very blunt, not produced in P. leleupi), and some other characters of minor importance. The shape of the aedeagus in dorsal view is intermediate between that of P. u nc i na tu s and P. leleupi. The large sclerotized plate in the endophallus of the new species does not seem to be homologous with that of P. uncinatus, as this plate is much longer in the new species and is located closer to the basal part of the aedeagus (this difference is even more noticeable when considering the position of the other copulatory pieces).
Distribution. Pachytrechodes brevis sp. n. is the first member of the genus found outside of the Uluguru Mountains, where all the previously described species were found (Jeannel 1960, Uéno 1987). The type locality of the new species is situated in an eastern part of the Udzungwa Mountains, approximately 110 km southwest of the type localities of P. uncinatus and P. l e l e u p i (Fig. 5). The Uluguru and Udzungwa mountains are two distinct neighboring blocks of the Eastern Arc Mountains.
Key to species of Pachytrechodes (modified from Uéno, 1987)
1 Smaller species, body length less than 2.50 mm; elytra smaller, ratio maximum elytral width / maximum pronotal width normally lower than 1.48; aedeagus smaller, not gutter-shaped; endophallus armature without large uncinate copulatory piece near apical orifice......................................................................................... 2
- Larger species, body length 2.70 mm or more; elytra larger, ratio maximum elytral width / maximum pronotal width usually higher than 1.50; aedeagus larger and heavily sclerotized, gutter-shaped, nearly enveloping endophallus which bears a large uncinate copulatory piece near apical orifice. Southern part of the Uluguru Mts: Lukwangule Plateau..................................................................................................... P. uncinatus Uéno, 1987
2 Body length 2.15–2.45 mm. Pronotum less transverse (on average ratio width/length 1.40). Elytra less wide, with more oblique humeri. Median lobe of aedeagus rather poorly sclerotized except for the ventral part, the apex not attenuated in profile, blunt or pointed. Endophallus armature without large acuminate copulatory piece in proximal part of aedeagus........ 3
- The smallest species of the genus, body length 2.0– 2.2 mm. Pronotum more transverse (on average, ratio width/length 1.45), its shape approximately as in P. uncinatus. Elytra wider, with more distinct humeri. Median lobe of aedeagus more strongly sclerotized, its apex distinctly attenuated in profile. Endophallus armature with a large acuminate copulatory piece in proximal part of aedeagus (Figs. 3–4). Eastern part of the Udzungwa Mts..................................... P. brevis sp. n.
3 Eyes flat; elytral striae shallower, stria 1 abbreviated near base; aedeagal apical lobe narrow and slightly reflexed in profile; endophallus armed with a single claw-like copulatory piece near apical orifice; Central part of the Uluguru Mts: Kidunda Mt............................................................................... P. basilewskyi Jeannel, 1960
- Eye slightly convex; elytral striae deeper, stria 1 usually traceable to base; median lobe of aedeagus very short and more or less blunt in profile; endophallus armed with at least two copulatory pieces lying one after the other at the median part. Southern part of the Uluguru Mts: ca. Chenzema Village............................................. P. leleupi Uéno, 1987 Discussion
Members of the subtribe Trechodina are mostly ripicolous. So far, only a very few humicolous trechodines are known. Apart from Pachytrechodes, Himalotrechodes insignis Uéno, 1981 and Thalassophilus caecus Jeannel, 1938, which were all discussed by Uéno (1987), there are three more species of the humicolous genus Scaurotrechodes Geginat, 2006 described from the South African Cape region (Geginat 2006, 2011). Surprisingly, the only known member of the humicolous genus Himalotrechodes Uéno, 1981, from the eastern Himalayas, demonstrates much more affinities with African Pachytrechodes (Uéno 1981) than the latter with members of Scaurotrechodes. This similarity is related to the reduction of hind wings, small eyes, swollen tempora, less strongly impressed frontal furrows etc., characters which may have evolved independently in various taxa when originally ripicolous lineages adapt to the humicolous microhabitats of the forest floor. On the other hand, the four species of Pachytrechodes, in addition to the above set of adaptive characters, share a similar shape of the aedeagus and the structure of the copulatory pieces, what suggests a monophyletic relationship between them, a hypothesis also supported by their geographic distribution restricted to the neighboring areas of the Uluguru and Udzungwa Mountains (Fig. 5). Since the latter is the largest block of the Eastern Arc Mountains, it is expected that new species of Pachytrechodes will be therein discovered in the next future.
description: Published as part of Belousov, Igor A. & Nyundo, Bruno A., 2013, A new species of Pachytrechodes Jeannel, 1960 (Coleoptera: Carabidae: Trechinae) from Tanzania, with a key to species, pp. 65-73 in Zootaxa 3637 (1) on pages 66-72, DOI: 10.11646/zootaxa.3637.1.7, http://zenodo.org/record/283602