Strumigenys pilosula

A Dominican amber fossil species.

Identification
Baroni Urbani & De Andrade (2007) - A Strumigenys species resembling the fossil Strumigenys schleeorum but differing from it by having 4 standing hairs close to the vertexal margin instead of 2, by a pair of standing hairs close to the ocelli (no such hairs in schleeorum), and by the leading edge of scape without freely projecting hairs instead of with freely projecting hairs.

S. pilosula resembles another previously known Dominican fossil, Strumigenys schleeorum (compare the figures of the present study with Figs. 22 & 23 by Baroni Urbani & De Andrade, 1994). Both species share a peculiar mandibular shape, with relatively short, curved and pointed mandibles without differentiated apical teeth touching each other only at the apex when closed. This structure is unknown among extant Strumigenys and appears to characterize a now extinct Dominican amber clade.

Distribution
This taxon was described from Miocene Ants from Dominican Republic.

Nomenclature

 * † pilosula. †Strumigenys pilosula De Andrade, in Baroni Urbani & De Andrade, 2007: 168, figs. 58-60 (q.) DOMINICAN AMBER.

Queen
TL 2.30; HL 0.58; HW 0.30; SL 0.27; ML 0.14; EL 0.14; WL 0.67; CI 51.7; S I 90.0; MI 24.1.

Head strongly converging anteriorly and with round vertexal corners. Frontal lobes slightly expanded and convex. Antennal fossae ventrally with a marked carina visible in full-face view, straight, covering the lower margin of the scrobes and ending close to the upper border of the compound eyes. Compound eyes large, very protruding, occupying large part of the posterior half of the antennal scrobe, and largely visible in dorsal view. Ocelli developed. With the head in profile the scrobes are superficial, with the upper margin indistinct and the lower one marked anteriorly only. Lateral clypeal margin converging anteriorly into an anterior convex margin weakly tumuliform medially. Scapes weakly dorsoventrally compressed, with sub-round bend, slightly less than 1/2 of the head length and slightly surpassing the eyes posteriorly. Antennae with six joints. Apical funicular joint slightly longer than the rest of the funiculus. Mandibles about 1/2 of the head length, touching each other only at the apex when opposed, with slightly convex external borders. Internal border of the mandibles with a broad basal lamella followed by a row of minute, poorly differentiated denticles and by a single spiniform tooth. Labral lobes large and partially visible between the mandibles.

Mesosoma robust and gently convex in profile. Parapsidal furrows weakly impressed. Scutellum with the sides converging posteriorly and with the posterior border rounded. Basal face of the propodeum long and declivous posteriorly; its sides marginate and its dorsum gently concave. Area between basal and declivous faces of the propodeum with a lamellaceous, pointed, transparent tooth that prolongs to the declivous face as a broad lamella.

Petiole with a long neck and with the node high and convex. Ventral surface of the petiole without spongiform lamina. Petiolar node with marked posterior margin and without spongiform process. Postpetiole convex in profile and without spongiform processes.

Gaster oval. Base of the first gastral tergite with developed anterior transverse cuticular ridge.

Sculpture. Head, mesosoma, petiole and postpetiole minutely reticulate, the reticulation more superficial on the postpetiolar dorsum. Mesopleurae, lower metapleurae and gaster smooth.

Pilosity. Dorsum of the head and scapes with sparse, weakly remiform hairs, subdecumbent on the head and appressed on the scapes. Leading edge of the scapes without free hairs. Border of the clypeus with few, free, weakly remiform hairs pointed medially. Apicoscrobal hair slightly pointed. Cephalic dorsum with 4 standing hairs close to the vertexal margin and a pair of hairs close to the ocelli. Pronotal humeral hairs long. Sides of the mesonotum with 2 pairs of hairs, the anterior pair much longer and thicker than the posterior one. Dorsum of the mesonotum with 2 pairs of erect hairs, one pair close to the anterior border and the second close to the parapsidal furrows. Petiole with a pair of pointed hairs dorso-laterally. Postpetiole with 2 pairs of pointed hairs, the anterior pair dorso-lateral and longer, the posterior pair dorsal and close to the posterior border. Ventral surface of the postpetiole with a thick hair. Gaster with few erect pointed hairs.

Colour. Light brown.

Type Material
Holotype. winged gyne (unique) in Dominican amber (GOPC) No. H 10-190.

The unique pilosula example is embedded in a small, cut and polished, yellowish amber sample 0.5 x 0.5 x 1.5 cm containing only this specimen. The amber sample bears the No. H 10-190 in the GOPC. The preservation conditions are good, although the right side of the ant is slightly flattened.

Etymology
pilosulus is the diminutive of the Latin adjective pilosus (= hairy) and is referred to the smaller number of macro chaetae that differentiate this species from its closest relative. S. schleeorum Baroni Urbani.