Bothriomyrmex enigmaticus

Known from the Hispañola type material, B. enigmaticus is the only representative of this genus known form the Caribbean. One congener is known Costa Rica and the balance of the species in the genus occur in the old world.

Identification
Prebus and Lubertazzi (2016) - The following character combination distinguishes Bothriomyrmex enigmaticus from Bothriomyrmex paradoxus: palp formula 2,3; medial lobe of clypeus not strongly projecting: flat, or with a broad, shallow concavity anteriorly. Long, paired setae on medial clypeal lobe separated by 2/3 their length or more. Eyes large: OI 23.1–24.7. Head box-like, with occipital corners narrowly rounded.

Neotropical Bothriomyrmex (workers):


 * Palp formula 4,3 (see fig. 3d in Dubovikoff & Longino 2004); medial lobe of clypeus strongly projecting beyond the lateral lobes; anterior margin evenly rounded to flat, never concave medially; paired long setae on anterior margin of medial lobe separated by less than ⅔ of their length (Fig. 2a, see image in description section below). . . . . Bothriomyrmex paradoxus
 * Palp formula 2,3 (Fig. 2d); medial lobe of clypeus weakly projecting; anterior margin flat to broadly concave medially; paired long setae on anterior margin of medial lobe separated by 2/3 of their length or more (Fig. 2b, see image in description section below). . . . . B. enigmaticus

Distribution based on Regional Taxon Lists
Neotropical Region: Dominican Republic.

Biology
Bothriomyrmex enigmaticus is known from one collection on the north side of the island of Hispañola. The sampling took place in July 2015 during a Museum of Comparative Zoology expedition to the Dominican Republic. The new ant species was discovered while based at a guardhouse in the Toro Palomo sector on the SE side of the Loma Guaconejo Scientific Reserve, near the village of La Peonía, at 195 m in elevation. M. Prebus collected a partial nest containing workers and brood from decomposing wood at the top of a 1.5 m tall live sapling in the middle of a path leading west from the guardhouse. The habitat was scrubby secondary growth, roughly 100 meters from a more mature secondary lowland moist forest. Tapinoma litorale was abundant in this habitat; due to the superficial similarity of these two species, Bothriomyrmex enigmaticus was initially thought to have been a collection of T. litorale. The nest was not mixed; it consisted solely of B. enigmatus.

Lubertazzi 2017, unpublished: A subsequent visit to this location and a relatively intensive search for this species by 3 collectors did not yield any new collections.

Nomenclature

 * . Bothriomyrmex enigmaticus Prebus & Lubertazzi, 2016: 4, figs. 2b-e, 3, 4 (w.l.) DOMINICAN REPUBLIC.
 * Status as species: Lubertazzi, 2019: 77.

Worker
(n=11): CL 0.541–0.563 (0.554); ClyW 0.375–0.412 (0.395); CS 0.520–0.542 (0.531); CW 0.495–0.523 (0.508); dAN 0.181–0.215 (0.197); EL 0.124–0.137 (0.132); EW 0.096–0.109 (0.105); EYE 0.112–0.122 (0.118); F2W 0.062–0.070 (0.065); IF2 1.000–1.222 (1.117); MGr 0.019–0.030 (0.024); MW 0.318–0.357 (0.343); PoOC 0.251–0.274 (0.260); PH 0.214–0.250 (0.231); PrL 0.264–0.296 (0.282); SL 0.407–0.434 (0.424); WL 0.572–0.617 (0.600).



Palp formula 2,3; distal maxillary palp segment roughly twice as long as basal (Fig. 2d). Medial hypostoma absent (Fig. 2e). Masticatory margin of mandible with 6 teeth and 1–2 denticles. Mandibles with short, curved setae similar to those on the anterior clypeal margin. Clypeus narrow: 0.10–0.11 mm high medially. Anterior clypeal margin flat, or with a broad, shallow concavity; bearing many short, curved setae; one long seta on each side of concavity, their bases separated by the length of the setae or more. Medial lobe of clypeus not strongly projecting. Posterior margin of clypeus even with anterior surfaces of antennal socket cavities. Antennal scapes short, not reaching the posterior margin of the head in full face view. Head slightly oblong (CL/CW 1.069–1.108), with lateral margins evenly convex; widest part of head in full-face view posterior to the compound eyes. Posterior head margin flat, becoming slightly concave medially; corners of head narrowly rounded, giving the entire head a blocky appearance. Head with two long setae on frons (longer than the first funicular segment) and two shorter setae on posterior clypeal margin (shorter than the first funicular segment), otherwise covered uniformly with short, dense, decumbant pubescence. Eyes large (EYE/CS 0.214–0.229), 8 ommatidia in longest row.

Posteroventral pronotum margin narrowly rounded. Metanotal groove deeply impressed. Propodeum high and rounded, with declivitous face roughly twice as long as dorsal face in profile; propodeal angle indistinct. Mesosoma covered uniformly with short, dense, decumbent pubescence.

Petiolar node in profile scale-like and strongly inclined anteriorly, with the anterior face much shorter than the posterior face (Fig. 2c). Ventral margin of petiole with a large lobe. Several setae present on the posteroventral margin of lobe.

Second, third and fourth tergites of gaster with long, erect setae arising from the middle of the tergite: two on the second, six on the third and fourth. First four sternites of gaster also bearing two long setae similar to those found on the tergites. Pubescence similar to the rest of the body, but becoming longer on the posterior margins of the sclerites.

Uniformly light brown; coxae and legs somewhat lighter.

Larva
Shape dolichoderoid. Body with two ventrolateral protuberances on prothorax which are fused ventrally by a narrow ridge; setae very short and limited to the prothorax; 8 pairs of spiracles. (Fig. 4).

Type Material
Holotype worker. DOMINICAN REPUBLIC: Provincia Maria Trinidad Sanchez, 7 km WSW El Factor, 19.29776° N, 69.94977° W ±3 m, 195 m ±5 m, 21 Jul. 2015, disturbed broadleaf moist forest, nest in dead top of live tree, M.M. Prebus#MMP01990 MCZ-ENT00035850. Paratypes. DOMINICAN REPUBLIC: Provincia Maria Trinidad Sanchez, 9 workers, same collection as holotype (: CASENT0756066; : CASENT0756067; : CASENT0756068; : MCZENT00539146, MCZ-ENT00539147; 18.106; : CASENT0756071; : CASENT0756072; : CASENT0755363).

Etymology
The specific epithet is derived from the ancient Greek “αινιγματικός”, meaning “riddle”, and bears a double entendre: not only is this the second species in this genus with a paradoxical distribution, this species also presents a puzzling new perspective on the generic classification system of the tribe Bothriomyrmecini.