Centromyrmex Mayr

Bolton, Barry & Fisher, Brian L., 2008, Afrotropical ants of the ponerine genera Centromyrmex Mayr, Promyopias Santschi gen. rev. and Feroponera gen. n., with a revised key to genera of African Ponerinae (Hymenoptera: Formicidae), Zootaxa 1929, pp. 1-37 : 4-6

Centromyrmex Mayr

Centromyrmex Mayr, 1866: 894 . Type-species: Centromyrmex bohemanni Mayr, 1866: 895 , by monotypy. [Junior synonym of Ponera brachycola Roger, 1861: 5 (synonymy by Kempf, 1967: 405).]

Spalacomyrmex Emery, 1889: 489 . Type-species: Spalacomyrmex feae Emery, 1889: 491 , by monotypy. [Synonymy with Centromyrmex by Emery, 1890b: 40.]

Glyphopone Forel, 1913: 308 . Type-species: Glyphopone bequaerti Forel, 1913: 308 by monotypy. [Synonymy with Centromyrmex by Brown, 1963: 9.]

Leptopone Arnold, 1916: 163 [as subgenus of Glyphopone ; raised to genus by Wheeler, W.M. 1922: 647; synonymy with Centromyrmex by Brown, 1963: 9]. Type-species: Glyphopone (Leptopone) rufigaster Arnold, 1916: 163 , by original designation [Junior synonym of Glyphopone bequaerti Forel, 1913: 308 (synonymy by Brown, 1963: 10)].

Typhloteras Karavaiev, 1925: 128 . Type-species: Typhloteras hamulatum Karavaiev, 1925: 129 , by monotypy. [Synonymy with Centromyrmex by Brown, 1953: 8.]

Diagnosis of worker and queen (gyne)

Workers are known for all species; queens are known for bequaerti , decessor , fugator , sellaris , raptor and angolensis of the Afrotropical region, for alfaroi , brachycola and gigas of the Neotropical region, and for feae and hamulatus of the Oriental and Malesian regions.

1 Mandible triangular (MI 28–38) to elongate-triangular (MI 52–84), with 4–12 teeth; with a distinct basal groove but without a basal pit.

2 Palp formula 4,3.

3 Eyes absent in worker, present in queen.

4 Frontal lobes with their anterior margins considerably posterior to the anterior clypeal margin.

5 Antenna with 12 segments; scape very strongly dorsoventrally flattened in its basal half, the leading edge extremely thin; funiculus gradually incrassate towards the apex but without a differentiated club.

6 Mesotibia, mesobasitarsus and metabasitarsus with strongly sclerotised spiniform or peg-like traction setae.

7 Pretarsal claws small, simple.

8 Metanotal groove absent.

9 Orifice of metapleural gland a small pore or short slit that opens laterally, located well above the ventral margin of the metapleuron and far anterior of the posteroventral angle of the mesosoma.

10 Propodeum unarmed.

11 Helcium located close to mid-height on anterior face of the first gastral segment (abdominal segment III).

12 Prora present but of unusual form and sometimes very weak; see discussion below.

13 Girdling constriction between presclerites and postsclerites of second gastral segment distinct.

14 Stridulitrum absent.

15 Queen only. Eyes and ocelli present. Transverse suture present on the mesopleuron that divides the sclerite into anepisternum and katepisternum. Mesosoma with full complement of flight sclerites. Hind wing with jugal lobe present.

Discussion of female characters

Character 9, in italics, is autapomorphic. Some of the other characters may also be apomorphies but have analogues that have apparently developed convergently elsewhere in tribe Ponerini . Characters 1–14 together form an inclusive diagnosis that isolates Centromyrmex workers and queens from all other genera in the tribe.

1 In the bequaerti group the mandibles are triangular and relatively short, with a small number of strongly defined teeth and a distinctly inflected apical tooth. In all other groups the mandibles are elongate-triangular, pointed apically but without an inflected apical tooth as the latter continues the line of the long axis of the mandible, and with more weakly defined but more numerous teeth on the masticatory margin. The small teeth on the elongate-triangular mandibles are commonly very worn and rounded, leaving the margin with a crenulate or even an almost edentate appearance.

2 The consistent palp formula count of 4,3 has been confirmed in alfaroi (worker and queen), angolensis (worker and queen), bequaerti (worker (all size morphs) and queen), brachycola (worker and queen), decessor (worker and queen), ereptor (worker), feae (worker), fugator (worker and queen), hamulatus (worker), raptor (worker and queen) secutor (all worker size morphs), sellaris (worker and queen). PF 4,3 was earlier recorded for all Neotropical species by Kempf (1967). This consistent count is probably an apomorphy of the genus (the same count also applies in all known males, see below).

3 Loss of eyes in the worker caste but their retention in queens is also characteristic of Promyopias : see discussion of potential genus group, below.

5 Extreme flattening of the basal half of the scape allows it to fit tightly against the dorsum of the head when directed laterally or posteriorly. Presumably this is an adaptation that allows the scapes to remain easily mobile in very confined spaces.

6 The apparent cuticular spines on the mesotibia, mesobasitarsus and metabasitarsus are in reality hypertrophied sclerotised setae, with sockets at the base. Their function is to improve traction in the ant’s restricted habitat. They also occur in the same locations in Promyopias and Feroponera : see discussion of potential genus group, below.

8 All species lack any trace of a metanotal groove. Indeed, in all but alfaroi there is usually no trace of any suture across the dorsum at the junction of mesonotum and propodeum, so that the line of the posterior termination of the mesonotum is not demarcated in any way. In alfaroi a short, unimpressed, weak transverse suture is retained.

9 The unique position of the metapleural gland orifice is given as an unequivocal autapomorphy of Centromyrmex ; it is a derived state not repeated anywhere else in the Ponerini , where the position of the orifice is always at or very near to the posteroventral corner of the mesosoma, opening laterally or posteriorly.

11 Position of the helcium is similar in Promyopias and Feroponera : see discussion of potential genus group, below.

12 In the C. bequaerti group the prora is a flat transverse plate, slightly indented medially, that traverses the first gastral sternite below the helcium. In all other species groups the prora is represented by a pair of longitudinal ridges on the anterior face of the first gastral sternite, one on each side below the helcium (extremely reduced in alfaroi and raptor ); the space between the ridges is usually shallowly concave. The morphology of the former can easily be derived from that of the latter by emphasising and elevating the ridges and elevating the cuticle between the ridges. Prorae of this nature are not “normal” for Ponerini , which typically have a cuticular prominence, variously shaped, immediately below the helcium.

Diagnosis of male

Examined for alfaroi , angolensis , bequaerti , decessor and sellaris ; also previously described for feae and hamulatus .

1 Mandible very reduced, almost lobate; edentate or with a small apical tooth.

2 Palp formula 4, 3 (in situ counts).

3 Frontal lobes absent; antennal sockets fully exposed.

4 Antenna with 13 segments, filiform.

5 Second funicular segment very short, only as long as, or at most 1.10 × longer than, the short scape.

6 Eyes large, inner margin shallowly convex to shallowly concave, without a marked concavity or indentation in about the median third; ocelli prominent.

7 Notauli variable, see discussion below.

8 Parapsidal grooves present.

9 Mesonotum with a deep, transverse groove between mesoscutum and mesoscutellum.

10 Epimeral lobe present.

11 Metapleural gland orifice present.

12 Propodeal spiracle with orifice elliptical to slit-shaped.

13 Spurs of mesotibia and metatibia as in worker and queen, see below.

14 Mesotibiae, mesobasitarsi and metabasitarsi lack the spiniform setae that are so conspicuous in female castes.

15 Pretarsal claws simple.

16 A membranous arolium present between the pretarsal claws.

17 Hindwing with jugal lobe present.

18 Prora usually present, its structure as in respective worker and queen but reduced in size; absent in alfaroi .

19 Gastral segment 2 (= abdominal segment IV) with a distinct girdling constriction between presclerites and postsclerites.

20 Pygidium (= abdominal tergite VIII) without a median apical spine.

21 Cerci (= pygostyles) present.

Males are known for few Afrotropical species, and very few specimens of each exist. The paucity of material makes it impossible to predict which characters will be of value at species-rank in this sex. For this reason, formal descriptions are not presented in the treatment by species.