Proceratium lunatum

Proceratium lunatum is known to occur in Cameroon, Gabon and Uganda where it was collected in rainforests at elevations ranging from 110 to 1520 m. The known specimens were either collected from within the soil or sifted litter suggesting that P. lunatum is a predominantly hypogaeic species. (Hita Garcia, Hawkes and Alpert 2014)

Identification
Hita Garcia, Hawkes and Alpert (2014) - The following character combination distinguishes P. lunatum from the other Afrotropical members of the P. arnoldi clade: eyes strongly reduced (OI 3–5), usually consisting of a single ommatidium, rarely more; head slightly longer than broad (CI 92–95); maculae on vertexal angles of head well developed and conspicuous; mesopleurae weakly to moderately inflated posteriorly; petiolar node high nodiform, anteroposteriorly compressed, with anterior face relatively straight; petiole in dorsal view between 1.2 to 1.3 times wider than long DPeI 122–129; ventral process of petiole lamelliform and approximately rectangular, lamella not significantly pointing anteriorly nor posteriorly; abdominal segment IV between 1.0 to 1.2 times longer than abdominal segment III (ASI 104–118); head, mesosoma and petiole with mat of short decumbent to subdecumbent pubescence only, without any longer, fine suberect to erect hairs.

The recognition of P. lunatum within the P. arnoldi clade is fairly easy and straightforward. The relatively broad head in full-face view (CI 92–95) groups it together with Proceratium burundense, Proceratium nilo, Proceratium sali and Proceratium sokoke (CI 91–95) while it separates it from Proceratium arnoldi and Proceratium carri that have thinner heads (CI 85–87). The lack of long, standing pilosity on top of a dense mat of much shorter pubescence distinguishes P. lunatum from P. carri, P. nilo, P. sali and P. sokoke. The species closest to P. lunatum seems to be P. burundense. However, both differ in eye size, ventral process of the petiole, and propodeal armament. Proceratium lunatum has smaller eyes (OI 3–5) and shorter propodeal teeth than P. burundense (OI 8). In addition, the ventral process of the petiole has a very distinct posteroventral corner that strongly projects ventrally, whereas the process of P. lunatum is more or less rectangular without a projecting posteroventral corner.

The P. lunatum material from Cameroon and Gabon shows no observable intraspecific variation. The specimen from Uganda, however, displays some noticeable differences. It possesses longer antennal scapes (SI 71 vs. SI 63–66) and is generally larger than the western specimens (TL 3.43 vs. TL 2.81–2.94).

Baroni Urbani and de Andrade (2003) - A member of the arnoldi clade. Differing from its sister species, Proceratium burundense, by the larger and deeper integumental foveae and by the deeper sculpture on the gaster in the worker. Both species have foveolate sculpture on their gaster.

Keys

 * Key to Afrotropical Proceratium Species
 * Key to Afrotropical species of the Proceratium arnoldi clade

Distribution based on Regional Taxon Lists
Afrotropical Region: Cameroun, Gabon, Uganda.

Nomenclature

 *  lunatum. Proceratium lunatum Terron, 1981: 96, fig. 1 (w.) CAMEROUN. See also: Baroni Urbani & De Andrade, 2003b: 290.

Worker
Baroni Urbani and de Andrade (2003) - Head slightly longer than broad, its sides gently diverging posteriorly. Vertex in full face view almost straight in the middle, in full dorsal view flat and bearing on each side a round, semitransparent macula. Clypeus medially reduced, subconvex or almost straight, between and as long as or slightly longer than the antennal sockets. Anterior border of the clypeus minutely crenulate. Antennal socket with broad torulus. Frontal carinae slightly distant from each other, partially covering the antennal insertions. Frontal area concave posteriorly, the concavity connected to a longitudinal carina prolonging posteriorly. Lateral expansions of the frontal carinae narrow, slightly raised, diverging on the two anterior thirds and slightly converging on the posterior third. Genal carinae marked, each carina corresponding to the external border of a deep sulcus. Eyes small, recognisable as a dark dot below the integument and placed on the midline of the head. First funicular joint slightly longer than broad. Funicular joints 2-10 broader than long. Last funicular joint about as long as the sum of joints 7-10. Scapes much short of the vertexal margin and gently thickening apically. External border of the mandibles concave. Masticatory margin of the mandibles with 3 denticles before the pointed apical tooth. Palp formula 3,2.

Mesosoma convex in profile and as long as the maximum head length (mandibles included). Basal face of the propodeum gently declivous posteriorly. Area between the basal and declivous faces of the propodeum gently concave. Basal and declivous faces of the propodeum separate laterally by a lamellaceous tooth. Sides of the declivous face of the propodeum with a broader and obtuse posteriorly lamella. Lower mesopleurae with well defined sutures, their posterior half inflate and smooth. Propodeal spiracle round and above mid height in lateral view.

Petiolar node convex in profile, the dorsum of the node declivous posteriorly and bearing an irregular point postero-medially. Petiole in dorsal view with diverging sides on the anterior sixth and convex posteriorly. Anterior border of the petiole almost straight and carinate, the carina angulate on each side. Ventral process of the petiole lamellaceous, subrectangular, the lamella slightly pointed posteriorly. Postpetiole anteriorly broader than the petiole; its sides gently convex. Postpetiolar dorsum with a postero-medial, transparent, raised bulla below the integument. Postpetiolar sternite anteromedially with a marked subtriangular projection. Postpetiolar sternite in side view strongly convex posteriorly. Constriction between postpetiole and gaster impressed. Gastral tergite I convex on the curvature and with a postero-medial transparent, raised bulla below the integument. Remaining gastral tergites and sternites curved ventrally.

Legs slender but not very elongate. All tibiae with a pectinate spur. Spurs of fore legs without basal spine. Fore basitarsi longer than the mid ones. Hind basitarsi about 1/4 shorter than hind tibiae. First tarsomere of hind legs subequal in size to the pretarsus. Pretarsal claws simple. Arolia developed.

Sculpture. Head, mesosoma, petiole, postpetiole and gaster irregularly foveolate and granulate, the foveae slightly shallower and sparser on the head. Gaster with additional longitudinal, irregular, thin rugosities. Legs punctate.

Body covered by hairs of three main types: (1) short, dense, subdecumbent on the whole body, slightly shorter, sparse and suberect on the funicular joints; (2) longer than type (1), very sparse and subdecumbent on the whole body, rare and slightly shorter on the scapes, slightly denser, longer and more raised on the propodeum, on the petiole, on the postpetiolar sternite and on the femora; (3) shorter than hair type (1), dense and decumbent on the funicular joints only. In addition the funicular joints bear whitish, thick, appressed, short, sparse hairs.

Colour. Light ferrugineous-brown with lighter antennae and legs.

Measurements in mm and Indices: TL 2.93-2.95; HL 0.71-0.73; HW 0.67-0.68; EL 0.03-0.04; SL 0.47-0.49; WL 0.85-0.86; PeL 0.28-0.29; PeW 0.34-0.36; HFeL 0.52-0.54; HTiL 0.44-0.45; HBaL 0.33; LS4 0.18-0.19; LT4 0.48-0.52; CI 93.0-94.4; SI 66.2-67.1; IGR 0.36-0.38.

Type Material
Baroni Urbani and de Andrade (2003) - Type locality: Mbalmayo, Kala and U. O. Bikok, Cameroon. Type Material: holotype worker labeled Cameroun: Arboretum de Mbalmayo (51 km D de Yaounde), 17.III.1968, G. Terron leg., Proceratium lunatum Terron, Holotype, 1759 sp. 1", in CIRA; one paratype worker labeled: Cameroun: Kala (18 km W Yaounde), Ve Berlese, sp. 1, tamisage terre et terreau, 16.V.1974, G. Terron Leg., Paratype in CIRA; two paratype workers labeled "1759, Mbalmayo, Cameroun, 17.III.1968, Paratypus, Proceratium lunatum, G. Terron, 1981" in, ; one paratype worker labelled "UO Bikok Cameroun, 19.III.1974, (G. Terron); Paratypus. Proceratium lunatum Terron", in, examined.