Microdaceton

Four species are now known in this small but very compact genus; all are restricted to the Afrotropical region. Microdaceton tibialis and Microdaceton exornatum are widely distributed, respectively in western and central Africa, and eastern and southern Africa. The other two (Microdaceton tanyspinosum, Microdaceton viriosum) remain known respectively only from Cameroun and Gabon, and Uganda.

Species by Region
Number of species within biogeographic regions, along with the total number of species for each region.

Nomenclature

 *  MICRODACETON [Myrmicinae: Dacetini]
 * Microdaceton Santschi, 1913g: 478. Type-species: Microdaceton exornatum, by monotypy.
 * [Microdaceton also described as new by Santschi, 1914e: 33.]

Description
Bolton (2000)
 * Mandibles linear and elongate, with kinetic mode of action, each with an apical fork of 3 spiniform teeth that interlock at full closure. *Preapical dentition absent. Mandibles at full gape open to 170° or more.
 * Basal process of mandible a curved spur; at full mandibular closure process is dorsal to labrum and fits into a mediodorsal impression on labrum.
 * Basimandibular gland bulla conspicuous on ventral or ventrolateral surface.
 * Palp formula 3, 2.
 * Labrum roughly T-shaped, short and not capable of reflexing to conceal the labio-maxillary complex, which is permanently exposed . Each lateral labral arm locks into a deep emargination near the inner mandibular base.
 * Trigger hair appears as single hair, arising from midpoint of anterior margin of the labrum.
 * Eye not located ventrolaterally on side of head.
 * Side of head with an extensive gap between base of mandible and margin of head capsule when mandibles fully closed.
 * Antenna with 6 segments, with a weakly differentiated apical club of 2 segments. Funicular segments 2 - 3 not reduced; long and slender, usually at least as long as funicular segment 4 (preapical segment).
 * Scape, when laid back in its normal resting position, passes above the eye; apical portion of extended scape curved anteriorly when seen in full-face view; scape not abruptly downcurved near base.
 * Scrobe absent.
 * Pronotal cervix anteriorly with an abruptly raised thick transverse rim or collar that is preceded by a broad deep transverse groove.
 * Pronotal humeri unarmed ; mesonotum with a pair of tubercles or teeth.
 * Propodeal spiracle very close to margin of declivity, at approximately the midheight of the sclerite. Metapleural gland bulla with its apex very close to the propodeal spiracle.
 * Waist segments without spongiform tissue; petiole node bidentate; postpetiole markedly dorsoventrally flattened and expanded into lateral wings; postpetiolar spiracles ventral, on undersides of the lateral expansions.
 * Limbus absent from first gastral tergite; basigastral costulae present or absent.
 * Suture between first gastral tergite and stemite angulate laterobasally.
 * Bizarre pilosity never developed.

The single median trigger hair on the labrum appears in fact to be composed of a pair of hairs that are tightly fused together. Generally the structure appears single even using electron microscopy (Bolton, 1999), but in small specimens of tibialis maceration in sodium hydroxide sometimes results in the separation of the two components.

Baroni Urbani & De Andrade (2007) - The following characters result apomorphic for this genus:

Worker (and gyne) pronotal cervix with thick transverse rim. CI 1.00, RI 0.00.

Worker (and gyne) maxillary palps three-jointed. CI 0,85, RI 0.80. Among the Dacetini the three-jointed condition is known only in Phalacromyrmex and Pilotrochus.

Worker (and gyne) labial palps two-jointed. CI 0.70, RI 0.67. Among the Dacetini the two-jointed condition is known in Phalacromyrmex, Pilotrochus, Ishakidris and some Basiceros species.

Other plausible generic synapomorphies not included in our data matrix are listed by Bolton (1999) [see above].