Centromyrmex

Bolton, B. & Fisher, B. 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 : 4-10

Genus Centromyrmex

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 x 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.

Discussion of male characters

None of the characters listed are unequivocally stated as apomorphic at present, but 2 is a strong contender for this status and 5 and 11 are possibilities.

1 A reduced mandible of this form appears apomorphic for the tribe Ponerini as a whole (Bolton, 2003).

2 The 4,3 palp formula of males and the female castes is the same in all Centromyrmex where both are known. Elsewhere in Ponerini it is usual for males to have higher palp formula counts than conspecific females (Bolton, 2003), so this equality of PF is most probably an apomorphy of the genus. The plesiomorphic maximum count in Ponerini males is 6,4 (as in Aculeata in general), as opposed to 4,4 in females

(Brown, 1963; Bolton, 2003).

5 In Ponerini generally the second funicular segment of males is much longer than the scape (e.g. Ogata, 1987; Yoshimura & Fisher, 2007; Bolton & Fisher, 2008). It is not certain whether the very short condition in Centromyrmex is plesiomorphic or apomorphic.

6 In many groups of Ponerini the inner margin of the eye is distinctly concave or suddenly indented in approximately its median third (e.g. Ogata, 1987; Yoshimura & Fisher, 2007).

7 Notauli are distinctly present in decessor , angolensis and most sellaris. However, in one example of sellaris only the anterior portions of the notauli were developed and in another the notauli were present but superficial throughout. Notauli were entirely absent in all alfaroi and bequaerti males examined.

11 A metapleural gland orifice is visible in all males. Unlike the female castes, males have the orifice in the usual position for Ponerini, close to the posteroventral angle of the metapleuron. The presence of this structure in this sex is uncommon and may be an apomorphy of the genus.

13 In the male of bequaerti both the mesotibia and metatibia have two spurs, on each the anterior spur is small and simple, the posterior is large and pectinate. In alfaroi the mesotibia has a single small, barbulate spur and the metatibia a large pectinate spur. In angolensis , decessor and sellaris the mesotibia lacks spurs and the metatibia has only a single pectinate spur present. These arrangements correspond to those of the female castes of the same species.

16 The arolium is usually white, membranous and very conspicuous.

Comment

The four genus-group names listed in the taxonomic synopsis above as long-standing junior synonyms of Centromyrmex are all confirmed here. Promyopias , an earlier, fifth junior synonym most recently catalogued in Bolton (2003), is removed from synonymy and reinstated at genus-rank as discussed below.

Synonymic synopsis of species

I Afrotropical species

bequaerti group

bequaerti (Forel, 1913)

= rufigaster (Arnold, 1916)

secutor Bolton & Fisher sp. n.

feae group

angolensis Santschi , 1937 stat. n.

decessor Bolton & Fisher sp. n.

ereptor Bolton & Fisher sp. n.

fugator Bolton & Fisher sp. n.

longiventris Santschi , 1919 stat. n.

praedator Bolton & Fisher sp. n.

raptor Bolton & Fisher sp. n.

sellaris Mayr , 1896

= constanciae Arnold , 1915 syn. n.

= arnoldi Santschi , 1919 syn. n.

= congolensis Weber , 1949 syn. n.

= arnoldi r. guineensis Bernard , 1953 syn. n.

II Oriental and Malesian species

feae group

feae (Emery, 1889)

= donisthorpei Menozzi , 1925

feae subsp. ceylonicus Forel , 1900

feae subsp. greeni Forel , 1901

hamulatus group

hamulatus (Karavaiev, 1925)

III Neotropical species

brachycola group

alfaroi Emery , 1890

brachycola (Roger, 1861)

= bohemanni Mayr , 1866

= brachycola var. paulina Forel , 1911

gigas Forel , 1911

Key to world species groups of Centromyrmex (workers and queens)

1 Mesotibia with 1 or 2 spurs. Procoxa not hypertrophied. Protibia not inflated. Pronotum not marginate anterodorsally .............................................................................................................................................. 2

- Mesotibia without spurs. Procoxa hypertrophied. Protibia inflated. Pronotum marginate anterodorsally. (Afrotropical, Oriental, Malesian)................................................................................................ feae group

2 Mesotibia with 1 spur. Propodeal spiracle not high on side, not very close to dorsal margin of mesosoma. Apical tooth of mandible weakly or not differentiated, not inflected but more or less continuing the line of the long axis of the mandible. Monomorphic species.................................................................................3

- Mesotibia with 2 spurs. Propodeal spiracle high on side, very close to dorsal margin of mesosoma. Apical tooth of mandible strongly differentiated and inflected, not continuing the line of the long axis of the mandible. Polymorphic species. (Afrotropical).......................................................................... bequaerti group

3 Ventral process of petiole consisting of two stout teeth. Metasternal process a pair of elongate, narrowly triangular spines. Mesotibial spur pectinate. (Malesian) ................................................... hamulatus group

- Ventral process of petiole consisting of a single keel. Metasternal process a pair of low rounded tumuli or low triangular crests. Mesotibial spur simple to weakly barbulate. (Neotropical)........... brachycola group

I Afrotropical species

Key to Afrotropical species (workers)

NOTE. The few known queens will also run in this key, except characters relating to shape of mesosoma in workers do not apply to queens.

1 Mesotibia with two spurs. Metatibia with two spurs, the anterior spur smaller and simple, the posterior spur larger and pectinate. Propodeal spiracle high on side, close to dorsal outline and at about the midlength of the sclerite. Pronotum not marginate anterodorsally. In profile the propodeal dorsum continues the line of the mesonotal dorsum. Subpetiolar process large, keel-shaped. Metasternal process bispinose. Polymorphic species. ( bequaerti group) ............................................................................................ 2

- Mesotibia without spurs. Metatibia with a single large pectinate spur only. Propodeal spiracle low on side, far from dorsal outline. Pronotum marginate anterodorsally. In profile the propodeal dorsum slopes steeply down from the line of the mesonotal dorsum. Subpetiolar process a short slender spine or small triangular tooth. Metasternal process not bispinose. Monomorphic species. ( feae group) ......................... 3

2 With mesosoma in profile the bulla of the metapleural gland is short and does not extend to near the base of the propodeal spiracle. Metatibia with spiniform setae such as are seen on the mesotibia. Protibia ventrally with a single stout spiniform seta, similar to those on the mesotibia, located close to the apex on its outer surface, anterior to and opposite the large spur. (Cameroun, Gabon, Central African Republic, Democratic Republic of Congo, Angola, Malawi, Zambia, Zimbabwe).............................................. bequaerti

- With mesosoma in profile the bulla of the metapleural gland is long and extends to, or even touches, the base of the propodeal spiracle. Metatibia without spiniform setae such as are seen on the mesotibia. Protibia ventrally without a stout spiniform seta that is similar to those on the mesotibia, at most a simple slender seta located close to the apex on its outer surface, anterior to and opposite the large spur. (Gabon) ........................................................................................................................................................... secutor

3 Petiole node in dorsal view conspicuously broader than long.....................................................................4

- Petiole node in dorsal view at least as long as broad, usually distinctly longer than broad........................9

4 Apical third of metatibia with a total of more than 3 thickly spiniform setae that arise from its anterior surface opposite the pectinate spur; one or more thickly spiniform setae also arise from the dorsal (outer) surface of the metatibia in the apical third of its length...................................................................................5

- Apical third of metatibia with only 1-2 (extremely rarely 3) thickly spiniform setae that arise from the apex of its anterior surface, opposite the pectinate spur; no thickly spiniform setae arise from the dorsal (outer) surface of the metatibia in the apical third of its length...................................................................6

5 Mandible with 5-6 main teeth that are separated by diastemata, the latter are unarmed or have indistinct low crenulations present. With base of gaster in absolute profile the prora is visible as a distinct raised cuticular crest that extends from the base of the helcium onto the anteroventral surface of the first gastral sternite. Smaller species with narrower head and shorter mandibles, HW 1.20-1.34, PW 0.94-1.12, CI 102-105, MI 71-75. (Cameroun, Gabon, Democratic Republic of Congo)................................... decessor

- Mandible serially dentate, with 10-12 teeth; all teeth are similar in size and without diastemata separating them. With base of gaster in absolute profile the prora is undeveloped, lacking a raised cuticular crest that extends from the base of the helcium onto the anteroventral surface of the first gastral sternite. Larger species with much broader head and longer mandibles, HW 1.92-2.02, PW 1.50-1.62, CI 119-123, MI 82- 84. (Zambia, Zimbabwe).................................................................................................................... raptor

6 Anterior apex of metatibia with a single thickly spiniform seta, approximately opposite the pectinate spur. (Liberia, Ivory Coast, Ghana, Cameroun, Gabon, Central African Republic, Democratic Republic of Congo, Angola)............................................................................................................................ angolensis

- Anterior apex of metatibia with two thickly spiniform setae, approximately opposite the pectinate spur..7

7 CI 108-118; at low magnification and in full-face view the head capsule appears conspicuously broader than long. Mandibles relatively slightly longer, MI 68-75. Larger species, HW 0.90-1.13. (Guinea, Ivory Coast, Ghana, Nigeria, Cameroun, Gabon, Democratic Republic of Congo, Uganda, Kenya, Zambia, Mozambique, Zimbabwe).................................................................................................................. sellaris

- CI 98-101; at low magnification and in full-face view the head capsule appears slightly longer than broad or about as long as broad. Mandibles relatively slightly shorter, MI 59-64. Smaller species, HW 0.65- 0.81 .............................................................................................................................................................. 8

8 With mesosoma in profile the slope of the anterior portion of the propodeum is steep and slopes abruptly from the mesonotum. Smaller species, HW 0.65-0.68, WL 1.06-1.14. (Cameroun, Gabon) longiventris

- With mesosoma in profile the slope of the anterior portion of the propodeum is shallow and slopes only weakly from the mesonotum. Larger species, HW 0.79-0.81, WL 1.31-1.34. (Gabon, Central African Republic, Democratic Republic of Congo)....................................................................................... ereptor

9 Basal margin of mandible, from basal tooth to basalmost curve, shallowly convex; basal margin much shorter than masticatory margin. Larger species, HL 1.06, HW 0.99, PW 0.82. (Democratic Republic of Congo)........................................................................................................................................... praedator

- Basal margin of mandible, from basal tooth to basalmost curve, shallowly concave; basal margin almost equal in length to masticatory margin. Smaller species, HL <0.90, HW <0.85, PW <0.70. (Democratic Republic of Congo, South Africa)..................................................................................................... fugator

Centromyrmex bequaerti 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 bequaerti , where it is weakly delineated). Propodeal spiracle slit-shaped and close to metanotalpropodeal 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 hamulatus forms an almost perfect morphological intermediate between the two groups. For distribution of shared and independent characters see under hamulatus , below.