Polyrhachis revoili species-group

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

Species

Identification

Bolton (1973) - Characterised by the partial or total loss of the margination of the alitrunk, the reduction or disappearence of the dorsal sutures of the alitrunk, and a tendency towards the reduction of sculpturation. All species in the group except Polyrhachis aenescens have abundant long, erect hairs on all dorsal surfaces of the head and body, and a majority have long hairs on the appendages also.

This group is considered to have developed from the viscosa group. In the important character of the loss of margination of the alitrunk a number of species are known which are intermediate between the groups of viscosa and revoili. The transition from a fully marginate to a completely immarginate condition is illustrated by the following series of species: Polyrhachis durbanensis → Polyrhachis transiens → Polyrhachis aenescens → Polyrhachis otleti → Polyrhachis regesa → Polyrhachis revoili. In the first species, a member of the viscosa group, the alitrunk has complete margination. The second species shows complete margination of the pronotum whilst the mesonotum and propodeum are very weakly and obtusely margined, the latter more weakly so than the former. The propodeal margination is lost in aenescens, and in otleti only the pronotum retains margins. In regesa the pronotal margination is weak and only extends for part of the length of the segment. No trace of margination remains in the last species of the series.

The dorsal sutures of the alitrunk are very much reduced, especially the metanotal groove. Apart from Polyrhachis platyomma in which it is distinct, the groove is represented in most species only by a very faint line which may fail to break the sculpturation in places. In Polyrhachis volkarti the metanotal groove is completely absent, and in Polyrhachis khepra both dorsal sutures are supressed. The pronotal spines decrease in size as one moves away from the species most similar to those in the viscosa-group and the intensity of sculpturation lessens, until in Polyrhachis braxa the spines are represented by a pair of very small teeth and the integument is smooth and highly polished. In most species the sculpturation is similar to that found in the viscosa group, that is, reticulate-punctate overlaid by rugulation or a rugoreticulum.

Propodeal armament is variable; in some species a pair of upcurved teeth are present but in others these are reduced to tubercles or are entirely absent. A modification found in some species of the group is the development of transverse propodeal ridges which separate the dorsum from the declivity. In all species where these ridges are present they are incomplete medially, with a small but distinct gap between them.

The petiole follows the pattern described for the militaris complex, the majority of species having a pair of long dorsal spines with a smaller lateral pair. The latter tend to be diminished in size in certain species and only a pair of minute teeth or tubercles remain in species such as Polyrhachis lanuginosa and Polyrhachis khepra.

Notes

Bolton (1973) - The distribution of the species of the revoili-group is mostly confined to the forested areas of West and Central Africa and Uganda. Only revoili itself is found outside this area, in eastern and southern Africa.

Some of the earlier described species of the revoili-group were placed by Emery (1925:206) in his subgenus Pseudocyrtomyrma, which he erected in 1921, designating revoili as the type-species. In fact, he included the following species in the subgenus: Polyrhachis alexisi, Polyrhachis curta, Polyrhachis kohli, lanuginosa, Polyrhachis platyomma, revoili and Polyrhachis spitteleri. As is now understood, only the third to fifth named (the third being a synonym of volkarti) are close to revoili, whilst the rest have different affinities. That the subgenus was poorly defined at its inception is shown by the fact that spitteleri is included whilst Polyrhachis monista, its closest relative, is not; Polyrhachis curta is included whilst Polyrhachis maynei, a synonym, was grouped with Polyrhachis laboriosa; and alexisi was apparently included as it did not fit in with any other species known at that time. With the removal of these species one is left with the nucleus of the revoili-group as it is understood at the present time, but the existence of species intermediate between the viscosa-group and Pseudocyrtomyrma, and the other similarities with both the viscosa- and militaris groups shows that the formal subgeneric name is untenable.

Related Pages

Polyrhachis
subgenus Myrma
Key to Afrotropical Polyrhachis species-groups
Key to Afrotropical Polyrhachis species

References