Propodilobus, Branstetter, Michael G., 2009

Branstetter, Michael G., 2009, The ant genus Stenamma Westwood (Hymenoptera: Formicidae) redefined, with a description of a new genus Propodilobus, Zootaxa 2221, pp. 41-57 : 54-55

Propodilobus gen. n.

( Figures 41–44 )

Type species: Stenamma pingorum DuBois (replacement name for Stenamma orientale , junior homonym).

Gender: Masculine

Etymology: The name is descriptive of the prominent propodeal lobes found on the type specimen. It is a combination of propodeum, which is the first abdominal segment in apocritan Hymenoptera , and lobus, L., meaning lobe.

Diagnosis of worker. With characters of the Myrmicinae as described by Bolton (2003), and the following more specific features:

1. Mandibles elongate triangular with 6 teeth which decrease in size irregularly from apex to base; teeth on basal half reduced and poorly defined.

2. Palp formula 3,2.

3. Apex of anterior clypeal margin smoothly convex.

4. Anterior clypeal margin lacking a strong isolated median seta.

5. Median portion of clypeus lacking longitudinal carinae.

6. Posteromedial margin of clypeus narrowed and prolonged backward between frontal lobes.

7. Frontal lobes small and closely approximated, not entirely covering antennal insertions.

8. Antennal scrobes and frontal carinae absent.

9. Antenna 12 segmented and terminating in a distinct 3-segmented club (ACI 74-75).

10. Promesonotum convex and prominent in profile.

11. Metanotal groove present.

12. Propodeum armed with a pair of well-developed spines.

13. Propodeal lobes present and elongate, bluntly triangular in shape and directed posterodorsally; space between lobes and propodeal spines distinctly U-shaped.

14. Middle and hind tibiae lacking spurs.

15. Pretarsal claws small, simple.

16. Petiole with a long, anterior peduncle; anteroventral process lacking.

17. Postpetiole broader than long.

Discussion. Propodilobus can be distinguished from Stenamma by the reduced palp formula (3,2 versus 4,3), smoothly convex anterior clypeal margin, distinct 3-segmented antennal club (ACI 74-75 versus 60-70), and elongate propodeal lobes. In addition, the postpetiole is broader than long and the scape and funiculus of Propodilobus have a more robust appearance than in Stenamma .

Propodilobus may be confused with Lordomyrma since Lordomyrma is morphologically diverse and currently lacks an adequate diagnosis. It is possible that when a more comprehensive morphological review of Lordomyrma is undertaken or the phylogenetic position of Propodilobus is tested with molecular data, Propodilobus will be synonymized under Lordomyrma or a related genus. Despite this, from the diagnoses listed in Sarnat (2006) and Taylor (2009), Propodilobus can be distinguished from Lordomyrma by its lack of longitudinal carinae on the clypeus, lack of scrobes and frontal carinae, the presence of an elongate petiolar peduncle, and the presence of elongate propodeal lobes.

Describing a new genus from a few specimens of one species should generally be avoided. However, no currently described genera have the above combination of characters and in an effort to create a monophyletic Stenamma , I believe that this action is defensible. In addition, by erecting a new genus, there might be greater interest in discovering new material for future systematics studies.

Distribution. As reported in DuBois (1998), P. pingorum is known only from two localities on the island of Borneo in Sarawak, Malaysia. These are the type locality (listed below) and Fourth Division, Gunong Mulu National Park (Feb 1978, N.M. Collins, BMNH).

Figures

FIGURES 41 – 44. Images of Propodilobus pingorum CASENT 0171177 (Sarawak, Malaysia). Figures 41 – 43: Full-face, profile, and dorsal views, respectively. Figure 44: Close-up of the elongate propodeal lobe in profile.