Genus Metalasius gen.nov.

ZooBank LSID. urn:lsid:zoobank.org:act:AC5A1489-C805- 4035-A1C0-3DDBC6E1206D.

Type species. Lasius myrmidon Mei, 1998: 177, figs 1–11 (w.). Original designation.

Species included. M. myrmidon (Mei, 1998) comb.nov., † M. pumilus (Mayr, 1868) comb.nov.

Total clade definition (worker).

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; Note 1).

6. Frontalcarinae conspicuous,> 0.5 × anteroposteriorantennal torulus diameter.

7. Frontal region of head, between antennal toruli strongly bulging, frontalcarinae raised above toruli (Note 2).

8. Antenna 12-merous.

9. Third antennomere broader than long (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 (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 (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 (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 (Note 6).

21. Pubescence of abdominal terga VI and VII linear.

Notes on definition:

Note 1. Modification of the anterior clypeal margin for reception of the labrum is here interpreted as a synapomorphy of Metalasius plus the core Prenolepis genus group. The modification is most easily observed in anterior or anterodorsal view. In most Formicinae, the perceived anterior clypeal margin with the head in full-face view is usually a carina which runs across the clypeus from the lateral clypeal margins.This carina may be raised or otherwise modified; regardless, the carina itself or the anterior region of the clypeus is produced anteriorly, concealing the clypeolabral articulation. In the Prenolepis and Metalasius genus groups, the clypeolabral articulation is usually exposed or nearly exposed laterally by notches in the anterior clypeal carina, although it may be exposed medially where the anterior clypeal carina is absent.

Note 2. See Note 1 for the Lasius genus group.

Note 3. Surprisingly, this distinguishes members of the Metalasius genus group from most formicine genera, with the exception of some Myrmelachista, various plagiolepidines and the Lasius flavus group. Cladomyrma species have a cone-shaped third antennomere, which is usually longer than the diameter of its base (and often apex), except in C. dianeae Agosti et al. for which the length and basal diameter are subequal. Some Pseudolasius and Paraparatrechina approach having subequal diameter and length.

Note 4. Mei (1998), in his diagnosis of Metalasius myrmidon, indicated that these standing setae were absent except for one specimen.

Note 5. This state may be a synapomorphy for the clade consisting of Metalasius plus the Prenolepis genus group.

It was not possible to evaluate this with confidence for † M. pumilus, but from the dorsal view of specimen SMFBE1226 on AntWeb, the gland does appear to be small.

Note 6. These characters could not be evaluated with confidence for † M. pumilus with the available material or descriptions. Etymology. A combination of the Greek ‘meta-’ (with, across, after) and ‘lásios’ (hairy), in reference to the former placement of the type species. Homophonously forming ‘metal-Asius’, invoking the death of the Trojan leader Asius during the assault on the Archaean wall of Troy. Masculine.

Comments. Although, we could not evaluate all of these characters for † M. pumilus, this species is consistently recovered as sister to M. myrmidon in combined analysis (Figs 4, S 7–S 9). Metalasius is most easily differentiated from both the Lasius and Prenolepis genus groups by the combination of mid-set eyes, the posteriorly directed and reduced metapleural gland orifice, raised frontal carinae and 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).