Proceratium nilo, Hita Garcia, Francisco, Hawkes, Peter G. & Alpert, Gary D., 2014

Hita Garcia, Francisco, Hawkes, Peter G. & Alpert, Gary D., 2014, Taxonomy of the ant genus Proceratium Roger (Hymenoptera, Formicidae) in the Afrotropical region with a revision of the P. arnoldi clade and description of four new species, ZooKeys 447, pp. 47-86 : 60-62

Taxon classification Animalia Hymenoptera Formicidae

Proceratium nilo sp. n. Figs 4A, 15A, 15B, 15C, 18

Type material.

Holotype, pinned worker, TANZANIA, Tanga, Korogwe, Nilo Forest Reserve, 4.91456S, 38.67712E, 1006 m, primary forest, collection code CEPF-TZ-4.1, 1.-4.IX.2005 (P. Hawkes, J. Makwati & R. Mtana) (SAMC: CASENT0235688).

Diagnosis.

Proceratium nilo can be distinguished from the other Afrotropical members of the Proceratium arnoldi clade by the following combination of characters: eyes absent; head slightly longer than broad (CI 91); maculae on vertexal angles of head well developed and conspicuous; mesopleurae extremely inflated posteriorly; petiolar node in profile relatively low, bluntly rounded nodiform, anterior face of petiole strongly produced anteriorly on lower third and not straight; petiole in dorsal view between 1.1 and 1.2 times wider than long (DPeI 115); ventral process of petiole well developed, lamelliform and rectangular, lamella not pointed anteriorly nor posteriorly; abdominal segment IV around as long as abdominal segment III (ASI 102); head, mesosoma and petiole with numerous long, fine, suberect to erect hairs on top of dense mat of much shorter decumbent to subdecumbent pubescence.

Worker measurements

(N=1). TL 3.31; EL n.a. (eyes absent); SL 0.56; HL 0.82; HLM 0.99; HW 0.75; WL 0.97; HFeL 0.60; HTiL 0.51; HBaL 0.40; PeL 0.34; PeW 0.39; DPeI 115; LT3 0.50; LS4 0.20; LT4 0.51; OI 0; CI 91; SI 68; IGR 0.39; ASI 102.

Worker description.

In full-face view head slightly longer than broad (CI 91), sides weakly convex, head not gently diverging posteriorly, vertex weakly convex. Clypeus medially reduced, its anterior margin convex to slightly triangular, only slightly protruding anteriorly, not surrounding the antennal sockets and not medially impressed, antennal socket with broad torulus. Frontal carinae relatively short and widely separated, not converging medially and strongly diverging posteriorly, partially covering antennal insertions; frontal carinae conspicuously raised on their anterior half, much less posteriorly. Eyes absent (OI 0). Mandibles elongate-triangular; masticatory margin of mandibles with four relatively small teeth/denticles, decreasing in size from larger apical tooth to basal denticle. Mesosoma weakly to moderately convex in profile and approximately as long as the maximum head length including mandibles. Lower mesopleurae with well impressed sutures, no other sutures developed on lateral or dorsal mesosoma; mesopleurae extremely inflated posteriorly; propodeum in profile armed with small, pointed teeth, propodeal lobes well developed, lamellate, rounded and blunt; declivitous face of propodeum between teeth and lobes noticeably concave; in posterodorsal view sides of propodeum separated from declivitous face by margin connecting propodeal lobes and propodeal teeth. Legs slender and elongate; pro- and mesotibiae with pectinate spurs; calcar of strigil without basal spine. Petiolar node in profile relatively low, bluntly rounded nodiform, anterior face of petiole strongly produced anteriorly on lower third and not straight, posterior face approximately straight, anterior and posterior faces not parallel, dorsum of node weakly rounded; petiole in dorsal view between 1.1 and 1.2 times wider than long (DPeI 115), petiolar node in dorsal view clearly much broader than long; ventral process of petiole well developed, lamelliform and rectangular, lamella not pointed anteriorly nor posteriorly. In dorsal view abdominal segment III anteriorly broader than petiole; its sides diverging posteriorly; dorsum of abdominal tergum III with posteromedial, very conspicuous, semitransparent, flat bulla below the integument; abdominal sternite III anteromedially with a marked subtriangular projection. Constriction between abdominal segment III and IV conspicuously impressed. Abdominal segment IV strongly recurved (IGR 0.39), conspicuously rounded on its curvature, especially posteriorly, abdominal tergum IV approximately as long as abdominal segment III (ASI 102); large, semitransparent and semicircular bulla situated posteromedially on abdominal tergum IV; remaining abdominal tergites and sternites relatively inconspicuous and curved ventrally. Whole body covered with dense mat of relatively short, decumbent to subdecumbent pubescence, and most of body with moderately abundant, much longer (several times longer than pubescence), suberect to erect, fine, standing hairs. Mandibles longitudinally rugose; most of body irregularly foveolate and/or granulate, sculpture best developed on cephalic dorsum, moderately so on mesosoma and petiole, especially weak, almost smooth, on most on anterior third of abdominal tergum IV, posterior third of abdominal tergum IV with conspicuous, longitudinal, irregular rugosity; inflated, posterior part of mesopleura and declivitous face of propodeum unsculptured, smooth and shining. Head, mesosoma (excluding posteriorly inflated part of mesopleurae), postpetiole and remaining abdominal segments of brown colour, mandibles, inflated part of mesopleurae and legs yellowish to light brown.

Etymology.

The name of the new species is derived from the type locality, the Nilo Forest Reserve in Tanzania. The species epithet is a noun in apposition and thus invariant.

Distribution and ecology.

Like several other species of the clade, Proceratium nilo is only known from a singleton holotype collected in the Nilo Forest Reserve in the Tanga region of northeast Tanzania (Fig. 18). Nilo covers an area of 5366 ha and, although the 9048 ha Amani Nature Reserve is significantly larger, Nilo is the largest of the 14 forest reserves in the East Usambara mountain range. The forest is largely undisturbed with a dense canopy cover (estimated at 90-95%) and little evidence of logging. Altitude within the reserve ranges from approximately 340 to 1500 m; the area surveyed was near the middle of this range at approximately 1000 m. The soil along the 230 m transect sampled varied from moist loamy sand to sandy clay loam (hand soil texture classification) and roughly 80% covered by an approximately 1 cm thick layer of leaf litter, with deeper accumulations in places. The single Proceratium nilo specimen was collected in pitfall trap 18 of 24 placed along the transect, and no further details of its microhabitat preferences can be determined.

Taxonomic notes.

Proceratium nilo is a fairly conspicuous member of the clade, and possesses a unique character combination allowing an easy identification. The most noticeable difference is the total lack of eyes, which are present in all the other species of the clade. Not considering the eyes, the shape of the petiolar node groups Proceratium nilo with Proceratium sokoke while it separates it from Proceratium arnoldi , Proceratium burundense , Proceratium carri , Proceratium lunatum and Proceratium sali . In the latter five the node is high nodiform, anteroposteriorly compressed and with the anterior face relatively straight, whereas the node shape of Proceratium nilo and Proceratium sokoke is relatively low, bluntly rounded nodiform with the anterior face strongly produced anteriorly on lower third. Despite the clear separation based on the presence/absence of the eyes, Proceratium nilo is morphologically very close to Proceratium sokoke . Indeed, the only significant difference is eye development, and for a short while we considered to lump them both under the same species name. However, the examination of many more species of Proceratium led us to refrain from doing so. As it seems, the presence or absence of eyes, as well as their specific development, is species-specific in the genus, which supports the separation into two species. Also, there are a few more differences. Proceratium sokoke has a longer abdominal tergum IV in relation to abdominal segment III (ASI 125) compared to Proceratium nilo (ASI 102). In addition, the head of Proceratium nilo does not significantly broaden posteriorly while the head of Proceratium sokoke does so. However, based on the very limited material this could just be within a normal species-specific range. The two-species hypothesis is also supported by different habitat preferences (littoral, mixed dry forest at a very low elevation vs. submontane, primary rainforest at a medium elevation). Future sampling in East Africa might provide additional evidence for their heterospecificity or not (if eye development turns out to be variable within species), but for the moment we prefer to describe Proceratium nilo and Proceratium sokoke as easily identifiable species and make them both available to the taxonomic community.

Variation.

Since this species is known only from the holotype there is no available information about intraspecific variation.