Strumigenys murphyi group

Strumigenys murphyi group Bolton (2000)

Species

Malesian-Oriental-East Palaeartic

Worker Diagnosis

Mandibles narrow, elongate and curvilinear, emerging far apart on the anterior clypeal margin and with only their extreme apices engaging at full closure. Proximal to apices with a wide gap between the blades, through which the labral lobes are visible. Dorsal surface of mandible basally with a transverse to oblique rim or edge that extends across the width of the blade in front of the anterior clypeal margin. Dorsum of mandible basally, between the rim and the clypeal margin, depressed. In profile mandible b lade suddenly narrowed basally, the dorsal surface angled downward before it passes below the anterior clypeal margin. MI 41-55.

Dentition. With 2-7 preapical small teeth or denticles. Apex of mandible with a nearvertical series of minute denticles between larger apicodorsal and apicoventral teeth.

Basal lamella of mandible reduced to a very narrow strip, not visible in full-face view when the mandibles are closed.

Labrum terminates in a pair of elongate narrow lobes that are triangular to conical.

Clypeus with anterior margin broad, transverse to shallowly convex over the prominent labrum between the mandibles. True lateral margins of clypeus extremely short before merging with the preocular carinae.

Clypeal dorsum hairless or with minute orbicular hairs; the anterior margin hairless or with a row of short projecting flattened hairs.

Preocular carina visible in full-face view.

Vertex of head at or near its highest point traversed by a raised ridge or crest that may be low and bluntly rounded or very sharply defined. Occipital lobes strongly expanded laterally, CI > 100.

Ventrolateral margin of head poorly defined in front of the eye, terminating anteriorly below the lowest point of the mandibular insertion. Postbuccal impression vestigial to absent.

Cuticle of side of head within the scrobe sculptured.

Scape short, SI 48-59, strongly narrowed basally, the shaft immediately distal of the narrowed portion projecting anteriorly as a large subbasal lobe; outline of scape crudely T-shaped, stem of the T offset from the centre.

Leading edge of scape distal to apex of subbasal lobe with a row of spatulate to spoon-shaped hairs that are curved either toward the base of the scape or the scape apex (rarely).

Pronotum dorsally without a median longitudinal carina, flat to shallowly transversely concave and bluntly marginate dorsolaterally. In profile the mesonotum forming a separate convexity or hump behind the pronotum. Dorsal outline of mesonotum usually impressed at about its midlength and convex posteriorly in front of the metanotal groove.

Propodeum without teeth but the declivity with a spongiform lamella running down each side.

Spongiform appendages of petiole and postpetiole moderate to massive, usually very extensive. Base of first gastral sternite in profile apparently without a spongiform pad (postpetiolar ventral lobes are so large that a sternal pad may be concealed ventrally between them).

Pilosity. Pronotal humeral hair absent. Dorsolateral margins of head in full-face view without projecting hairs. Standing hairs extremely sparse or absent from dorsa of head and alitrunk, numerous on first gastral tergite. Ground-pilosity of head of minute appressed hairs or very small orbicular hairs. Dorsal (outer) surfaces of middle and hind tibiae usually of small appressed apically-directed hairs; freely projecting long pilosity present in one species.

Sculpture. Cephalic dorsum finely reticulate-punctate.

Notes

The five species of this group have convergently acquired a habitus similar to that of the Palaearctic and Afrotropical Strumigenys argiola-group, but are mostly distributed in the Oriental and Malesian regions where the true argiola-group does not occur (both groups occur in Taiwan). They have independently acquired a similar form of mandible and scape, broadened occipital lobes and similar alitrunk shape. However, except for the elongation and narrowing of the mandibles (which has occurred independently many times within Pyramica) similar developments are also indicated, or are already strongly developed, in members of the extemena group. For instance lateral broadening of the occipital lobes, development of a subbasal lobe on the scape, and shape of the alitrunk, are all developed in the extemena-group, as well as in the murphyi-group and argiola-group.

In the original descriptions of Strumigenys extemena and Strumigenys murphyi Taylor (1968b) placed the former in its own genus, Dysedrognathus, and the latter in Epitritus, arguing that the morphology of the former gave an indication of the mode of evolution of the latter. The discovery of many more species in these groups has since made it clear that the true relationship is between the extemena- and murphyi-groups, and that the similarities of murphyi with genuine argiola-group species, that formerly constituted the genus Epitritus, are the results of convergence.

Two synapomorphies indicate that the murphyi-group is the sister of the extemena-group, and that together they form a monophyletic unit within Pyramica that excludes the species from direct relationship with former Epitritus species (the current argiola-group), no species of which shows any of these novel developments.

1 Development of a transverse ridge or crest across the highest point of the vertex.

2 Presence of an acute transverse to oblique rim or edge across the dorsum of the mandible basally.

References

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