Proceratium sokoke

Known only from the holotype. This worker was collected in a leaf litter sample from a tropical dry forest adjacent to the coast of the Indian Ocean.

Identification
Hita Garcia, Hawkes and Alpert (2014) - Proceratium sokoke differs from the other Afrotropical members of the P. arnoldi clade by the following character combination: eyes strongly reduced, consisting of a single ommatidium (OI 4); CI 92; maculae on vertexal angles of head well developed and conspicuous; 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 to 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 1.25 times longer than abdominal segment III (ASI 125); head, mesosoma and petiole with numerous long, fine, suberect to erect hairs on top of dense matt of much shorter decumbent to subdecumbent pubescence.

The identification of P. sokoke is straightforward within the P. arnoldi clade. Proceratium nilo and Proceratium sokoke are the only species of the P. arnoldi clade in which the petiolar node in profile does not have a straight anterior face; instead the lower third is produced anteriorly. In the other five species the anterior face is conspicuously straight. Proceratium nilo is relatively similar to P. sokoke, but the latter has eyes that are absent in the first. Not considering presence/absence of eyes, both species could be seen as conspecific. As discussed in detail in the taxonomic notes section for P. nilo, we prefer to treat them as heterospecific in this study since eye development appears to be relatively stable within species of Proceratium. In addition to petiolar node shape, P. sokoke (CI 92) has a thicker head than Proceratium arnoldi and Proceratium carri (CI 85–87), and its smaller eyes (O 4) and the rectangular ventral process of the petiole distinguish it from Proceratium burundense with its larger eyes (OI 8) and ventral process with an almost spiniform posteroventral corner. Furthermore, the presence of numerous long, fine, suberect to erect hairs on top of a dense mat of much shorter decumbent to subdecumbent pubescence is an additional character that separates P. sokoke from P. arnoldi, P. burundense and Proceratium lunatum.

Key to Afrotropical species of the Proceratium arnoldi clade

Distribution based on Regional Taxon Lists
Afrotropical Region: Kenya.

Biology
Proceratium sokoke is only known from the type locality, the Arabuko Sokoke Forest in Kenya, which is a tropical dry forest adjacent to the Indian Ocean coast (Fig. 18). As for most of its congeners, the natural history of this species is completely unknown. The holotype was collected from a leaf litter sample in a mixed forest habitat. Unfortunately, P. sokoke was only found in that one leaf litter sample and could not be recollected in the remaining 180 litter samples from Arabuko Sokoke, which means that it is either very rare or lives deep in the soil. With the background of the biology of the genus in general, we consider the latter most likely.

Castes
Known only from the worker holotype.

Nomenclature

 *  sokoke. Proceratium sokoke Hita Garcia, Hawkes & Alpert, 2014: 79, fig. 1D, 3B, 6A, 7A, 17A, 17B, 17C, 18 (w.) KENYA.

Description
pinned worker, KENYA, Coastal Province, Arabuko Sokoke Forest, 18° 51' 72 S, 39° 56' 26.6 E, 136 m, undisturbed and protected mixed forest, Winkler leaf litter extraction, collection code FHG00206, VI.2009 (F. Hita Garcia & G. Fischer) (MCZ: MCZ-ENT00520482).
 * Holotype

TL 2.47; EL 0.03; SL n.a.; HL 0.72; HLM 0.87; HW 0.66; WL 0.86; HFeL n.a.; HTiL n.a.; HBaL n.a.; PeL 0.30; PeW 0.35; DPeI 115; LT3 0.44; LS4 0.14; LT4 0.55; OI 4; CI 92; SI n.a.; IGR 0.25; ASI 125.
 * Worker measurements (N=1)

[Note: the holotype is partly damaged: antennae, one foreleg, one midleg and one hindleg missing, remaining hindleg broken at level of tibia]. Head longer than broad (CI 92), sides weakly convex, cephalic dorsum broader posteriorly than anteriorly; vertex in full-face view flat to 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 two thirds, much less posteriorly. Eyes very small (OI 4), consisting only of one ommatidium and located on mid line of head. 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 to 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 0.25), conspicuously rounded on its curvature, especially posteriorly, abdominal tergum IV around 1.25 times longer than abdominal segment III (ASI 125); 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 matt of relatively short, decumbent to subdecumbent pubescence; most of body with moderately abundant, much longer (several times longer than pubescence), suberect to erect, long, fine, standing hairs. Mandibles longitudinally rugose; most of body irregularly foveolate and/or punctate, sculpture best developed on cephalic dorsum, less so on mesosoma and especially weak on most of relatively smooth and shining abdominal tergum IV; inflated, posterior part of mesopleura and declivitous face of propodeum also only very weakly sculptured and relatively 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.
 * Worker description

The name of the new species is inspired by the type locality, the Arabuko Sokoke Forest in Coastal Kenya. The forest is the last larger remnant of the Coastal Forests of Eastern Africa in Kenya and hosts a unique fauna and flora. The species epithet is a noun in apposition and thus invariant.
 * Etymology