Polyrhachis viscosa species-group

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The species in this group are members of the subgenus Myrma.

Species

Identification

Bolton (1973) - This group of species is closely related to, and has probably developed from, the militaris group. The characteristics of the group include the reduction of the sutures of the alitrunk to faint, non-impressed lines and a reduction in the intensity of the lateral margination of the alitrunk, which in the present group of species is represented only by a low ridge or an acute angle and not as a projecting rim or flange as is so often seen in the militaris group. The basic sculpturation consists of a fine, dense, reticulate-puncturation which is usually overlaid on the head and alitrunk by a loose rugoreticulum. In Polyrhachis arnoldi, however, the ground sculpturation is overlaid and very much replaced by a fine, dense longitudinal striation which extends on to the gaster.

An interesting character found in this group is the development in many of its species of a transverse ridge running across the propodeum between the propodeal teeth or spines, and effectively separating the dorsum from the declivity. The development of the character is variable; for instance in Polyrhachis nigrita it is absent, in Polyrhachis spinicola present, but in most species in which the ridge occurs it is raised medially into a blunt tooth or tubercle, best developed in Polyrhachis cubaensis. The presence of a distinct, transverse propodeal ridge is noticeable in some species of other groups, namely Polyrhachis latispina of the militaris group and Polyrhachis lestoni and Polyrhachis limitis of the alexisi group.

Polyrhachis viscosa and related species are virtually devoid of erect hairs. In all species of the group hairs are restricted to the anterior clypeal margin and the gastral apex and only occasionally is a pair of hairs developed upon the dorsum of the head or alitrunk.

The petiolar structure in the group parallels that of the militaris group. The usual form is similar to that found in species closely related to Polyrhachis fissa, with the dorsal and lateral spines of approximately equal length, but there is a tendency towards the lengthening of the dorsal pair, best seen in Polyrhachis durbanensis.

Two species, nigrita and viscosa, show an increasing development of the lateral spines at the expense of the dorsals. As the laterals increase in size they tend to occupy the dorsolateral corners of the petiole so that the dorsal pair come to project from an almost flat surface running between the lateral spines. In viscosa the dorsals are still spiniform and a short but strongly sloping surface separates them from the laterals, but in nigrita the dorsals are reduced to a pair of teeth projecting from the almost flat surface between the very large lateral spines.

Notes

Bolton (1973) - All members of the group are restricted in distribution to savannah and veldt regions; none have been recorded from the forests of West and Central Africa.

Related Pages

References