Petalomyrmex

A monotpypic genus. Colonies of the single known species, Petalomyrmex phylax, are apparently polycalic and are situated within the internodes of the host plant Leonardoxa. The worker ants patrol young leaves of the host and protect them from herbivores. Older leaves are not patrolled but are protected by chemicals within the leaves. Sustenance for the ants is derived largely from specialized food bodies produced by Leonardoxa.

Identification
WORKER: Monomorphic: head cordate; antenna nine-segmented, without distinct apical club; ocelli near top of head. FEMALE: Antenna ten-segmented; head cordate, as broad as to broader than long; frontal carinae separated by more than their length; openings of propodeal spiracle and metapleural gland circular, latter with a few long guard hairs. MALE: Antenna ten-segmented; eye large, occupying most of side of head; ocelli normal; frontal carinae obsolete; pygostyles absent; mandible six-toothed.

This monotypic genus appears closely allied to Aphomomyrmex. The strongly cordate head of the worker will separate Petalomyrmex from Aphomomyrmex and related genera. Petalomrymex workers and females differ from those of Aphomomyrmex by the reduced palpal segmentation and the worker caste is monomorphic rather than polymorphic. The strong dorso-ventral flattening of the mesosoma of the Petalomyrmex female and male is unusual and distinctive; it is reminiscent of the bizarre females of the Neotropical subgenus Myrmostenus of Camponotus and of certain species of Myrmelachista. (Snelling 1979)

Distribution
Only known from Cameroon.

Nomenclature

 *  PETALOMYRMEX [Formicinae: Plagiolepidini]
 * Petalomyrmex Snelling, R.R. 1979: 5. Type-species: Petalomyrmex phylax, by original designation.

Worker
Monomorphic. Head cordate in frontal view. Apical margin of mandible oblique, with six distinct teeth, basal somewhat offset. Maxillary and labial palpi three-segmented. Median lobe of clypeus broader than long, entire apical margin of clypeus continuously gently convex; basal margin at about midpoint of antenna I sockets, lateral margin confluent with antennal sockets. Antennal scape reaching occipital margin; flagellum eight-segmented, without distinct club, only first and last segments longer than broad. Eye oval, at about middle of side of head; distance between eye and antennal socket much greater than distance between eye and margin of head in frontal view. Ocelli small but distinct, placed little below occipital margin. Occipital lobes distinct.

Mesosoma much as in Aphomomyrmex, but metanotum, in profile, distinctly convex and with spiracle minute, dorsal; opening of metapleural gland with a few long guard hairs.

Legs as in Aphomomyrmex.

Petiole about as in Aphomomyrmex, but spiracle about one-third of distance from base to summit of scale.

Head and body without appressed pubescence but with conspicuous erect hairs of varied length on all areas, including appendages.

Queen
Head about as in worker but occipital margin broadly concave so that head is not truly cordate. Mandible eight-toothed. Eye large, lateral, slightly below middle of side of head. Ocelli slightly enlarged, near occipital margin. Flagellum nine-segmented.

Mesosoma conspicuously flattened. Mesonotum flat, broader than long. Scutellum, metanotum and propodeum, in profile, continuously oblique.

Wings as in Aphomomyrmex.

Node of petiole low and thick in profile, with spiracle near summit; from above about twice wider than long; summit, from behind, much wider than base, broadly concave.

Gaster somewhat elongate.

Pilosity as in worker.

Male
Head, across eyes, distinctly wider than long. Eye massive, occupying most of side of head, interocular distance twice eye width in frontal view. Ocelli large, ocellocular distance about twice maximum diameter of anterior ocellus. Mandible four-toothed, preapical tooth often minute. Maxillary palp four-segmented, labial palp three-segmented.

Mesosoma similar to that of female, but proportionately a little broader. Legs slender. Wings as in female.

Petiole about as described for Aphomomyrmex; spiracle near summit of node.

Gaster robust. Pygostyles absent. Subgenital plate deeply excised. Paramere much longer than basal width, apex narrowly rounded. Ventral lobe of aedeagus weakly convex along lower margin, margin irregular but not dentate, basal angle rounded.

Body and appendages with numerous suberect to erect hairs of varied length.

Etymology
Petalos (Gr., flattened) + myrmex (Gr. Ant).