Strumigenys mnemosyne group

Strumigenys mnemosyne group Bolton (2000)

Species

Malesian-Oriental-East Palaeartic

Worker Diagnosis

Mandibles in full-face view and at full closure triangular, the masticatory margins engage throughout their visible length and are serially dentate. In ventral view outer margin of mandible without a prebasal inflected angle. MI 15-18.

Dentition. Basally with a dental row of 5 triangular teeth that are about equal in size. These are immediately followed by two slightly smaller teeth, 4 denticles (of which the basal most 2 are somewhat larger than the apical most 2) and a small apical tooth, giving a total dental count of 12.

Basal lamella minute to vestigial, at most a mere ridge on the margin proximal of the basal tooth, not visible in full-face view when the mandibles are fully closed.

Labrum terminates in a pair of narrow triangular to digitate lobes.

Clypeus with anterior margin transverse to shallowly concave across its entire width.

Sides of clypeus convergent anteriorly.

Clypeal dorsum with minute appressed pubescence or pubescence plus erect short simple hairs; clypeal margins with or without freely projecting hairs.

Preocular carina short and narrow in full-face view, usually only its lateral edge visible from posterior margin of clypeus to level posterior end of frontal lobe.

Side of head immediately below preocular carina with an elongate narrow depressed area of cuticle that is of different colour or texture from the surrounding cuticle and may be distinctly margined; the area may have a glandular function.

Ventrolateral margin of head between eye and mandible rounded to angular. Postbuccal impression deep and conspicuous.

Cuticle of side of head within the scrobe smooth and shining.

Scape short, SI 50-63, not strongly dorsoventrally flattened and without a flange-like leading edge.

Leading edge of scape usually with 2-3 straight simple hairs that project anteriorly or anterodorsally; less commonly without projecting hairs.

Pronotal dorsum without a median longitudinal carina.

Propodeum without trace of spines or teeth, the declivity on each side with a moderate to broad conspicuous lamella.

Spongiform appendages of waist segments massively developed in profile, but in dorsal view the posterior collar of the petiole node vestigial or absent. Base of first gastral sternite in profile with spongiform tissue feebly developed or absent.

Pilosity. Pronotal humeral hair present, simple, longer than others on the dorsum but not strongly differentiated from them. Simple standing hairs project freely from the dorsal surfaces of the head, alitrunk, waist segments and gaster. Freely projecting elongate simple hairs present on the dorsolateral margins of the head, the dorsal (outer) surfaces of the middle and hind tibiae, and the outer surfaces of the basitarsi.

Sculpture. Dorsum and sides of alitrunk, declivity of propodeum, waist segments and gaster all smooth and shining; head may also be smooth or have reticulate-punctate sculpture.

Notes

The 5 species currently recognised in this group are all minute and apparently rare. One species comes from Thailand, one from southern China, Taiwan and Japan; the remainding three originate in Borneo and one unidentifiable specimen from Java has been examined (see under Strumigenys runa). Doubtless more species await discovery in the Malay Peninsula and southern Oriental region.

Despite being very small the group is one of the most easily recognised in the region. The above characters in combination identify them immediately. The presence of a depressed and apparently glandular area below the preocular carina, and a very reduced basal lamella on the mandible are apomorphies, and all known species have minute eyes composed of a single tiny ommatidium. At species rank identification is rather more difficult; shortage of material renders some of the characters used rather speculative among the three Borneo species.

References

Bolton, B. 2000. The ant tribe Dacetini. Memoirs of the American Entomological Institute. 65:1-1028.