Metalasius myrmidon ( Mei, 1998 ) Boudinot & Borowiec & Prebus, 2022

Boudinot, Brendon E., Borowiec, Marek L. & Prebus, Matthew M., 2022, Phylogeny, evolution, and classification of the ant genus Lasius, the tribe Lasiini and the subfamily Formicinae (Hymenoptera: Formicidae), Systematic Entomology 47, pp. 113-151 : 141

Species Metalasius myrmidon ( Mei, 1998) comb.nov.

Definition (worker).

1. With character states of Metalasius .

2. Dorsal mandibular groove absent (Note 1).

3. Ventromedial base of mandible without trough or impression (Note 2).

4. Maxillary palps short, exceeding hypostomal margin but not reaching postgenal bridge midlength.

5. Maxillary palpomere 3 longest, 4 shorter but as long as 5 and 6 together (Note 3).

6. Clypeus, in lateral view, convex and weakly bulging anteriorly (Note 3).

7. Anterior tentorial pit situated lateral to midlength of the epistomal suture.

8. Lateral hypostomal carina absent (Note 4).

9. Compound eyes absent, reduced or vestigial, with at most 9 ommatidia (Note 5).

10. Propodeal spiracle situated distinctly in lower half of propodeum (Note 6).

11. Legs almost entirely devoid of standing setae (Note 3).

12. Petiolar node weakly inclined anteriorly, node well-developed, squamiform (Note 7).

Notes on definition:

Note 1. The dorsal mandibular groove is discernable in all examined Lasius and Prenolepis genus group taxa.

Note 2. Presence of a trough on the ventromedial base of the mandible is a newly detected synapomorphy of the core Prenolepis genus group. The impression is enhanced when the ventromedial mandibular margin is carinate and/or produced medially, and best seen when the mandibles are open and with the head in lateral anteroventral view. The trough may be reduced or absent in some species.

Note 3. Previously included in the original diagnosis of the species M. myrmidon by Mei (1998).

Note 4. The lateral hypostoma is usually delimited by a carina, which is discontinuous with the medial hypostomal lamina. Among formicines, the lateral hypostomal carina is absent only in Acropyga (some species) and Brachymyrmex , both genera outside of Lasiini .

Note 5. The specimens, which were available for examination had 5–8 ommatidia; the maximum ommatidium count is from Mei (1998, p. 178).

Note 6. Alowered propodeal spiracle appears sporadically replicated in only a few Prenolepis genus group members.

Note 7. The petiolar node is strongly inclined anteriorly in the core Prenolepis genus group.

Comments. Metalasius myrmidon is uniquely identified among the Lasiini by absence of the dorsal mandibular groove and lateral hypostomal carina, short and broad third antennomere, mid-set compound eyes (when present), which are reduced to at most 9 ommatidia and near complete absence of standing setae on the head. High magnification may be required to evaluate the lateral hypostoma.