Leptogenys arcuata

Identification
Lattke (2011) - Scape with abundant suberect hairs; hypostomal teeth not visible with head in full-face view; cephalic dorsum mostly smooth and shining with scattered piligerous punctulae; pronotum mostly smooth and shining, with few transverse rugulae on collar; propleuron mostly smooth and shining; metanotal groove scrobiculate.

A member of the arcuata species group.

Distribution
This taxon was described from Suriname. It is known from eastern Bolivia, Brazil, Lesser Antilles, French Guiana, Guadeloupe, Guyana and Saint Vincent and the Grenadines.

Castes
Queen, unknown. Male not examined.

Nomenclature

 *  arcuata. Leptogenys arcuata Roger, 1861a: 44 (w.) SURINAM. Forel, 1893g: 359 (m.). Senior synonym of deletangi: Lattke, 2011: 148.
 * deletangi. Leptogenys arcuata st. deletangi Santschi, 1921g: 87 (w.) BOLIVIA. Junior syonym of arcuata: Lattke, 2011: 148.

Lattke (2011) - This species can be confused with members of the more commonly encountered Leptogenys pubiceps complex, and the reader should consult the discussion for this complex for advice on how to separate the two. The examined type material consists of two point-mounted workers from Surinam, with the label bearing an additional, but partially illegible name “Deulschbein”. Perhaps it is a locality or the collector’s last name. Both specimens are in good condition but one lacks both antennae; and the other lacks only half of the funiculus. Santschi (1921) described Leptogenys deletangi because of its relatively shorter mandibles, broader head, and metatarsi longer than the tibia, though it is not clear if he meant the metatibia. Comparing the types of L. deletangi with the rest of L. arcuata specimens it was not possible to use Santschi’s diagnostic characters, nor any other characters, for considering such variation as anything more than intraspecific.

L. arcuata is the smallest species of its group. The Carajás series is on average smaller than the other specimens and very polished. L. arcuata usually shows no trace of the hypostomal teeth when the head is in full-face view, and only occasionally will a tooth apex manage to project beyond the clypeal margin. Nevertheless it is possible that the hypostomal tooth can be more prominent in some populations and this possibility was accounted for in the key. The anteroventral spot of node is flattened and smooth as in Leptogenys montuosa, but differs on account of larger hypostomal teeth than in L. montuosa, the larger size of L. montuosa, the striate propleuron of L. montuosa and the presence of punctae on the cephalic dorsum. Specimens of this species have been taken from under stones, and nests found in rotten logs (Forel 1893).

The specimen from French Guiana was identified as ''L. cf. arcuata as it differs from typical L. acuata'' in its slightly broader head, eyes more dorsolaterally placed on the head, noticeable hypostomal teeth in cephalic full-face view, smaller propodeal spiracle, elongate node with rougher lateral sculpturing, and a relatively longer subpetiolar process which lacks the ventral flat area. The dorsal propodeum margin in lateral view has its highest point anterad, implying a sharper curvature anterad, but this margin in L. arcuata is evenly convex. The traits of this single specimen were not taken into account for the description of L. arcuata as it could represent a different species, but a description should await the availability of additional material given its similarity with L. arcuata. L. arcuata is mostly South American, but has been taken on some Caribbean islands, indicating the possibility of tramp species capabilities. Forel (1893) describes the male from a nest series collected on the island of St Vincent.

Worker
Lattke (2011) - Metrics (n = 7): HL 0.88-1.00; HW 0.70-0.78; ML 0.52-0.58; EL 0.20-0.28; SL 0.82-0.92; PW 0.57-0.66; WL 1.40-1.60; PH 0.58-0.68; PL 0.38-0.44; DPW 0.40-0.48 mm. CI 0.77-0.80; MI 0.70-0.77; OI 0.26-0.36; SI 1.16-1.21; LPI 1.43-1.70; DPI 0.95–1.11.

Head semi-quadrate in full-face view, slightly longer than wide; lateral margins broadly curved and diverging anterad; posterior margin convex, slightly flattened medially. Eye convex and large, spanning more than one-fourth of lateral cephalic margin. Cephalic dorsum mostly smooth and shining with sparse, piligerous punctulae. Scape mostly smooth basad, becoming punctate apicad, surpasses posterior cephalic margin by one-fourth its length; length of antennal segment III usually less than double its width. Anterior clypeal margin laterally sinusoid, medially straight to slightly convex, medially overhung by triangular process about as long as wide, margins translucent, apex with 4-3 setae. Mandible slightly arched, parallel-sided with brief and weakly concave edentate masticatory margin, single apical tooth present; mandible leaves gap between clypeus when closed, at widest more than twice the mandibular width. PF: 4,4. Scape has abundant inclined hairs. Hypostomal tooth not visible in cephalic full-face view.

Mesosoma with prominent metanotal groove dividing dorsal margin in two large convexities in lateral view: promesonotum, and metanotum-propodeum. Pronotum mostly smooth and shining, with few transverse rugulae on collar; propleuron mostly smooth and shining. Mesopleuron varies from mostly smooth and shining with transverse striae along ventral area to mostly striate with smoother dorsomedian area; well-defined crest separates mesopleuron from mesosternum; metapleural-propodeal suture well impressed. Mesonotum with curved anterior margin in dorsal view, posterior margin mostly straight, dorsum smooth and shining. Metanotal groove more or less scrobiculate. Metapleuron and propodeum with transverse striae, propodeal dorsum mostly smooth, declivity transversely striate; spiracle opening oval, directed posterolaterally.

Node with semi-parallel anterior and posterior margins in lateral view; anterior margin shorter than posterior margin, anterior and posterior margins convex, anterior margin meets dorsal margin in sharp curve, dorsal margin meets posterior margin in abrupt angle. Node with longitudinal to oblique striae on sides; posterior face flattened, smooth and shining, distinctly separated from rest of node. Node as wide as long in dorsal view. Gaster smooth and shining with sparse punctulae. Anterior margin of abdominal segment III mostly vertical in lateral view. Head, mesosoma and abdomen black; clypeus, mandibles, antennae, and legs various shades of brown, usually ferruginous.

Type Material
Lattke (2011):

Syntype workers: Surinam (Deulschbein[?]) (ZMHB) [examined].

Leptogenys arcuata st. deletangi. Syntype workers: Bolivia, Camino de Aroyo Negro a Trinidad (Lizer, Deletang) (NHMB) [examined].

Additional References

 * [[Media:Lattke 2011.pdf|Lattke, J.E. 2011. Revision of the New World species of the genus Leptogenys Roger (Insecta: Hymenoptera: Formicidae: Ponerinae). Arthropod Systematics & Phylogeny 69:127-264. PDF]]