Metalasius

Metalasius contains two known species, the extant Metalasius myrmidon from Greece and the fossil species †Metalasius pumilus (from and ). These species, originally placed in Lasius, are now known to form the sister group to the Prenolepis genus-group (containing Euprenolepis, Nylanderia, Paraparatrechina, Paratrechina, Prenolepis, Pseudolasius and Zatania).

Identification
Total clade definition (worker) (Boudinot et al., 2022).
 * 1) With characters of Lasiini.
 * 2) Mandible with 6–8 teeth.
 * 3) Palp formula 6,4.
 * 4) Basal and masticatory mandibular margins meeting at a weakly oblique angle.
 * 5) Clypeus modified for reception of labrum (specifically, clypeus with anterolateral notches; see Boudinot et al. (2022), Note 1).
 * 6) Frontal carinae conspicuous, >0.5 × anteroposterior antennal torulus diameter.
 * 7) Frontal region of head, between antennal toruli strongly bulging, frontal carinae raised above toruli (see Boudinot et al. (2022), Note 2).
 * 8) Antenna 12-merous.
 * 9) Third antennomere broader than long (see Boudinot et al. (2022), Note 3).
 * 10) Compound eyes set at about head midlength.
 * 11) Ocelli absent.
 * 12) Dorsum of head completely without standing setae or with only a few small setae around each posterolateral head corner (see Boudinot et al. (2022), Note 4).
 * 13) Mesonotum, metanotum and/or propodeum discontinuous, metanotum undifferentiated medially.
 * 14) Mesopleural anterodorsal margin, near posterolateral region of pronotum, inconspicuously bulging, this weak shoulder a very narrow groove which traverses the mesosternum.
 * 15) Metapleural gland very small, orifice directed almost completely posteriorly (see Boudinot et al. (2022), Note 5).
 * 16) Propodeal spiracle situated in lower 2/3 of propodeum.
 * 17) Legs entirely or almost entirely devoid of standing setae.
 * 18) Petiole with raised squamiform node, without posterior elongation.
 * 19) Abdominal tergum III vertical, without deep groove for receiving petiole; not concealing petiole when gaster raised (see Boudinot et al. (2022), Note 6).
 * 20) Tergosternal suture of abdominal segment III not raised dorsally before unfusing near spiracle, rather anterior margin of abdominal sternum III directed anteriorly away from helcium before narrowly curving posteriorly (see Boudinot et al. (2022), Note 6).
 * 21) Pubescence of abdominal terga VI and VII linear.

Metalasius is most easily differentiated from both the Lasius and Prenolepis genus groups by the combination of:
 * mid-set eyes
 * posteriorly directed and reduced metapleural gland orifice
 * raised frontal carinae
 * almost complete lack of standing setae on the head.

In addition, both included species of Metalasius have broad third antennomeres and unusually small bodies relative to Lasius, being <2 mm in total length (Mei, 1998; Dlussky, 2011).

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

Nomenclature

 *  [Formicinae: Lasiini]
 * Metalasius Boudinot et al., 2022: 140. Type-species: Lasius myrmidon, by original designation.