Centromyrmex species groups

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These species groups were detailed in: Bolton, B. and B. L. Fisher. 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: 1-37. PDF

There is a key to the species groups, Afrotropical species and Neotropical species

bequaerti species group

Worker and queen (gyne). A small group of two Afrotropical species. Workers are known for both, the queen is known for bequaerti. Workers and queens with characters of the genus, listed above, and also the following characters diagnostic of the group, of which apomorphies are in italics.

Worker caste polymorphic.

Mandibles short, triangular (MI < 40 in workers) and with 4–7 teeth, the apical tooth differentiated and inflected.

Pronotum without margination either anteriorly or laterally.

Mesosoma in profile with dorsum of propodeum continuing the line of the mesonotum, the former not sloping steeply away from the latter.

Mesonotum behind promesonotal suture not elevated, not transversely marginate.

Metasternal process present as a pair of narrow erect spines that are very closely approximated and nearly parallel; the metasternal pit is between the spines posteriorly.

Propodeum in dorsal view broad, not strongly bilaterally compressed.

Propodeal spiracle in worker very high on the side and at about the midlength of the sclerite; orifice of spiracle long, slit-shaped.

Propodeal lobes low and rounded.

Procoxa not hypertrophied, only slightly larger than mesocoxa and metacoxa.

Mesotibia with two spurs: in all worker sizes the anterior spur is small, simple to barbulate. The posterior (main) spur is pectinate in large workers, but the pectination decreases with reduced size until, in the smallest workers, the spur is only barbulate.

Metatibia with two spurs: in all worker sizes the anterior spur is small, simple to barbulate. The posterior (main) spur is always broadly pectinate.

Petiole without an anterior peduncle; in profile the anterior face of the node rises from directly behind the anterolateral cuticular processes that protect the articulation.

Petiole node in profile becomes longer and lower as body size decreases.

Subpetiolar process large, roughly keel-like.

Prora conspicuous in profile as an elevated, roughly vertical ridge; in anterior view prora forms a transverse plate (slightly indented centrally) across the entire anterior face of the first gastral sternite.

Sculpture extremely reduced, the ants very smooth and shiny.

Standing setae present on all dorsal surfaces of head and body in worker, including dorsal surface of scape. Setae also present on ventral head and gastral sternites.

Queen only (bequaerti). Large eyes and conspicuous ocelli present. Mesosoma with full complement of flight sclerites. Transverse suture present on mesopleuron (absent or vestigial in workers except in largest examples of Centromyrmex bequaerti, where it is weakly delineated). Propodeal spiracle slit-shaped and close to metanotal-propodeal suture. Jugal lobe present on hindwing. Petiole node in profile much higher than long.

Comment

At first glance the species of the bequaerti group appear quite different from those of the feae group, and when taken in isolation their differences are arguably of genus-rank significance. However, the Malesian species Centromyrmex hamulatus forms an almost perfect morphological intermediate between the two groups. For distribution of shared and independent characters see under hamulatus, below.

brachycola species group

The Neotropical fauna of Centromyrmex was last revised by Kempf (1967), who recognised the three species listed. It seems likely that more species now await description in the main collections of South American ants. The three species are currently regarded as a single group, weakly defined by the characters noted in the key to world groups but further work may modify this arrangement.

In general the Neotropical species have mandibles shaped as in the feae and hamulatus groups, without a strongly developed, inflected apical tooth. An acute metasternal process is absent in alfaroi, where the structure of that part of the ventral mesosoma closely resembles that of the feae group: a pair of low, divergent tumuli. In brachycola the metasternal process is represented by a pair of widely separated, posteriorly divergent short crests that are low and triangular. Neither has the spiniform structure seen in the hamulatus and bequaerti groups. C. alfaroi, like bequaerti of the Afrotropical region, is known to be polygynous (Delabie, 1995).

feae species group

Eight Afrotropical species and the extralimital species feae, from the Oriental and Malesian regions, form a group of closely related species, the feae group, named for its first-described member. Workers and queens with characters of the genus, as listed above, and also with the following characters diagnostic of the group, of which apomorphies are in italics.

Worker and queen (gyne)

Mandible elongate-triangular and strongly downcurved (MI 52–84 in workers). Mandible pointed at apex but the point continues the line of the long axis of the mandible; there is no differentiated inflected apical tooth.

Mid-points of frontal lobes in workers separated medially by a narrowly triangular strip of cuticle, the mid-points of the lobes conspicuously not touching.

Frontal groove on mid-dorsum of head is broad and extends far posterior of the terminus of the frontal lobes.

Pronotum marginate anterodorsally; pronotal dorsum forms a plateau behind the anterior margination.

Mesosoma in profile with anterior portion of propodeum sloping down from the mesonotum so that the posterior half of the propodeal dorsum is on a much lower level than the mesonotal dorsum (worker only).

Metanotal groove absent (worker only).

Metasternal process absent. A thickly rounded oblique tumulus of cuticle arises on each side of the fully exposed metasternal pit; the tumuli diverge posteriorly and terminate at the metacoxae.

Propodeum unarmed, in dorsal view bilaterally compressed so that the dorsum is narrow.

Propodeal lobes extremely reduced to vestigial.

Orifice of propodeal spiracle subcircular to elliptical, abutting the bulla of the low metapleural gland.

Petiole with at least a short anterior peduncle.

Subpetiolar process small, in profile a short, slender spine or a small, acutely triangular tooth.

Procoxa hypertrophied, very swollen and much larger than the mesocoxa and metacoxa; in profile procoxa >> mesocoxa > metacoxa.

Protibia swollen and disproportionately large.

Protarsal segments 2–4 very strongly expanded laterally, deeply V-shaped, the apices of the V terminating in a very coarse spiniform seta on each side.

Mesotibia with spurs absent.

Metatibia with a single, large pectinate spur.

Metabasitarsus very short, at most only about half the length of the metatibia.

Prora represented by a pair of weakly divergent ridges on anterior face of first gastral sternite, one on each side below the helcium; space between the ridges shallowly concave (extremely reduced in Centromyrmex raptor).

Scapes and all dorsal surfaces of head and body with standing setae present except for sloping portion of propodeum, where they are completely absent, and posterior propodeal dorsum, where they are absent or represented by one to a few very short standing setae. Pubescence generally sparse to absent.

Queen only. Transverse suture present on the mesopleuron that divides the sclerite into anepisternum and katepisternum (absent in workers). Mesosoma with full complement of flight sclerites. Hind wing with jugal lobe present.

Comments

In most worker specimens the mesonotum appears to have a short elevated face immediately behind the promesonotal suture, and the top of this elevated face is usually equipped with a transverse margination. However, in isolated specimens within series the elevated face is absent. It is suspected that when the pronotum is fully flexed upward, the posterior margin of the pronotum slides up the short elevated anterior section of the mesonotum until the dorsal surfaces of the two sclerites are on the same level.

The habitus of feae group workers is distinctive, the most striking feature being the strange morphology of the legs. The forelegs appear fossorial and the middle and hind legs squat and spiny. All six are short, strong, and powered by the enormously developed coxae, especially the hypertrophied procoxae. Add to this the eyeless head with elongate-triangular, downcurved mandibles, extremely flattened scapes, anteriorly marginate and plateau-like pronotum, strongly sloping anterior portion of propodeum in profile and bilaterally compressed anterior propodeal dorsum, and the result is an appearance that is unlikely to be confused with any other ponerine ant in the region.

hamulatus species group

In morphological terms hamulatus forms a striking intermediary between the Old World species of the bequaerti group and the feae group, but it also has several apomorphies of its own.

i. Characters shared between workers of hamulatus and bequaerti group: shape of head capsule; close proximity of frontal lobes medially; non-swollen protibiae; lack of hypertrophy of procoxae; lack of pronotal margination; elongate slit-like orifice of propodeal spiracle; presence of spiniform metasternal process.

ii. Characters shared between workers of hamulatus and feae group: structure of mandible; dorsal outline shape of mesonotum and propodeum; position of propodeal spiracle; bilaterally compressed propodeal dorsum; petiole anteriorly pedunculate; form of prora; distribution of setae; monomorphic worker caste.

iii. Characters of hamulatus workers not shared by bequaerti or feae groups: mesotibia with 1 spur; metatibia with 1 spur; subpetiolar process a pair of stout teeth; mesopleuron with a weak transverse sulcus; constriction of second gastral segment strong and conspicuously cross-ribbed.