Metalasius pumilus ( Mayr, 1868 ) 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 pumilus ( Mayr, 1868) comb.nov.

Definition (worker).

1. With character states of Metalasius (Note 1).

2. Maxillary palps long, reaching occipital foramen (Note 2). 3. Compound eyes well-developed, with> 20 ommatidia.

4. Mesosomal dorsum devoid of setae.

5. Legs entirely devoid of standing setae.

6. Petiolar node weakly inclined anteriorly, node squamiform.

Notes on definition:

Note 1. Several characters could not be evaluated for † M. pumilus , including the ventromedial mandibular groove, palpomere proportions, clypeal profile, and lateral hypostomal carina.

Note 2. From Dlussky (2011).

Comments. We place † M. pumilus and M. myrmidon together based on the results of our phylogenetic analyses, and we interpret presence of the broad third antennomere and highly reduced cranial setation as synapomorphies of this clade. † Metalasius pumilus differs from M. myrmidon by the following: (i) compound eyes large; (ii) maxillary palps long, reaching occipital foramen, and (iii) standing setae completely absent from head dorsum and mesosoma.

Although, we have not examined the neotype of † M. pumilus , designated by Dlussky (2011) and deposited in Muzeum Ziemi Polskiej Akademii Nauk in Warsaw, the specimen we have studied is unlikely to be misidentified as it exhibits unique diagnostic traits of the species among the Lasiini , let alone of the Baltic amber fauna, including absence of setae on the head dorsum, well-developed eyes, short and broad third antennomere, and very small body size (<2 mm). Dlussky (2011) describes the eyes of both † L. schiefferdeckeri and † M. pumilus as ‘shifted somewhat posteriorly so that the length of [the] gena [is] more than [that of the] maximum diameter of [the] eyes’. This very general statement is true of both species, however, the eyes of † L. schiefferdeckeri are distinctly set in the posterior head half whereas those of † M. pumilus and M. myrmidon are situated at head midlength, distinguishing them from all Lasius genus group members.