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Extant: 8 valid species
Basiceros SchulzHNS 1906: 156 (replacement name for CeratobasisHNS; Meranoplus singularisHNS type species bymono- typy); Wheeler & Wheeler, 1954: 112 - 113 (larvae description); Brown & Kempf, 1960: 171 - 172 (worker and gyne diagnosis); Brown, 1974: 132 (worker, gyne and larvae diagnosis, male description; distribution and biology); Bolton, 2003: 183 - 184 (taxonomic history).
Worker: Size relatively medium (TL between 4,9 and 8,7 mm). Reddish to dark-brown in color. Integument thick and in general densely sculptured; foveolate over head disc, mesosoma with conspicuous deep to shal- lowly set punctuation, densely punctate over most or all the gaster. Pilosity conspicuous and bizarre; sub- decumbent hairs abundant, spatulate, squamiform or plumose; erect abundant or sparse hairs clavate or stout and truncate. Labrum with fine sensorial hairs. Head trapezoidal, triangular or rounded posteriorly; posterior and lateral head borders always visible and clearly distinct, and either rounded or crested, or else combined into curving, continuous or near continuous crest around posterior margin of head. Dorsal surface of head flattened to depressed, slightly convex in some species. Mandibles sub-por- rect, triangular to subtriangular, with straight, opposable, multidenticulate masticatory borders; apical portion from straight to strongly bent ventrally; basal portion flat and smooth to moderately convex and sculptured in frontal view; blade narrowed near insertion, the resulting peduncle either partly exposed or entirely hidden beneath clypeus, interspace between basal mandibular margin and anterior clypeal border present to absent in varying degrees. Eyes relatively well developed (ocular index ca 11). Antennal scape flattened, broad, and lobate at the basal portion; funiculus moderately clavate with 11 segments.
Mesosoma usually robust. Metanotal groove present. Propodeal teeth always triangular in lateral view, lamelliform, short, more or less acute, and connected to each other by a transverse carina. Petiole pedunculate and usually with ventral carina bearing one or more teeth. Gastric dorsum with a median longitudinal strip slightly impressed or devoid of pilosity. According to Brown (1974) BasicerosHNS has 5 Malpighian tubules.
Gyne: Like conspecific worker, with modifications expected for myrmicinegynes. Ocelli present. Prescutum usually longer than wide; notauli from almost indistinct to shallowly depressed; parapsidial lines shinning and usually indistinct from surrounding sculpture, deep to shallow parapsides; prescutellum with central area indistinct, scuto-scutellar sulcus from deeply to shallowly impressed or almost indistinct, with transversal rugulae varying in number; lateral wing of prescutellum projectingpostero-ventrally as a more or less developed hook-like structure; scutellum square-like or semicircular, with its posterior half always sloped down, posterior border concave. Metanotum median elevation bears a pair of specialized setae. Forewing with distinct and strongly colored stigma; longitudinal veins Sc + R, SR, M + Cu, and A present; SR extends distally beyond stigma as tubular vein for most of its length; M and Cu also extend distally, initially as tubular veins, then as spectral veins almost reaching distal wing border; cross vein M + Cu either absent, as an appendix of M or complete, thus forming open or closed M 1 cells; anal vein connected to M + Cu near branching point, either before, at or after. Hind wing with Sc + R extending shortly beyond point where they connect to M, which extends as tubular vein as much as Sc + R and then continues as spectral vein to wing distal border; basally M + Cu does not continue as tubular vein beyond junction with Anal vein, which is connected halfway to M and Cu branching point; tubular part of Cu is a mere stub, continuing as spectral vein distally; 5 sub-median hamuli present.
Male (modified from Brown, 1974): Slightly smaller and more slender than conspecific gynes. Color black with appendages somewhat lighter. Integument very finely and densely punctate, opaque or nearly so, including legs, mandibles and antennae. Head vertex with overlying loose rugulae, especially behind compound eyes and around ocellar triangle; loose rugulation also on alitrunk, especially on posterior half of mesonotum and sides of propodeum. In some species parts of mesopleura smooth and shining, or rugulose. Pilos- ity composed of fine tapered hairs, golden brown in color, mostly erect or suberect on body, but also ap- pressed on gaster and clypeus in some species; mandible, antennae and leg hairs becoming shorter, more abundant and decumbent passing from base to apex of these appendages.
Head broadest across large bulging eyes (situated at or slightly in front of head mid-length) rather suddenly narrowed in front of eyes and tapering moderately anterad; median vertex and ocelli prominent. Mandibles relatively developed, subtriangular, with curved outer borders converging rapidly in apical half; gently down curved and weakly convex dorsal faces. Masticatory borders bearing 8 - 12 serial teeth. Mandibles petiolate or not, when closed leaving or not a space between anterior border of clypeus and mandibles; in general labrum shape as in conspecific workers. Clypeus broad, truncate or rounded in front, extending to level of frontal lobes; its antero-lateral lobes concave, free margin with thin, sharp, yellowish edge, transverse or concave in front and rounded-di- vergent on sides. Frontal area variably distinct, semicircular or transverse, more or less impressed; rugose or carinate in the middle, and relatively well delimited behind by an arched carina or rugulae that tend to connect the two frontal lobes. Frontal lobes prominent and projecting forward, laterad and dorsad, their free margins rounded sharply in front and broadly laterad, antennal insertions located on their ventral faces. Lateral bases of lobes continued laterad as sharply raised arching carinae running close near the eye on each side, and then curving forward to bound deeply excavated, subreniform antennal scrobes bounded in front by cariniform posterior borders of lateral wings of clypeus. Posterior vertex bordered along cervical limit by lamelliform margin bearing short longitudinal costulae; space between this and posterior ocelli either steep or gradual, depending on whether head is much drawn out behind or not. A continuous, or nearly continuous, sharp but irregular, ventro-lateral carina extends from the posterior corner of head to mandibular insertion, bordering subrectangular area of cheek between eye and mandibular insertion, and bounded mesad by carinate outer scrobe margin. Antennae long and slender with 13 segments. Scape very short, only about twice as long as broad, its base oblique, with the more acutely rounded angle on outside, and obtuse angle inside, tapered towards truncate apex; a little thicker than remaining segments. Antennal segments 2 and 3 (counting from base) only about half as long as scape; succeeding segments all much longer than broad; apical segment longest; antennal segments 8 and 9 somewhat twisted, virtually making the antenna turns around its axis.
Alitrunk robust; prescutum with more or less distinct antero-median carina; notauli shallow to deep and complete, with transversal costulae. Parapsidial furrows shaped as fine shining lines; parapsides more or less impressed behind, but each with sharp, raised postero-lateral margin (hyaline in some species). Pres- cutellum separated from scutellum by an impression or transverse row of punctures, or else middle part impressed and not distinct from scutellum; lateral wings of prescutellum with laterally marginate, posteriorly pointed process or blunt hook-like structure. Scutellum much narrower than prescutellum, forming elongate near-semicircle as seen from above, free borders marginate, but postero-median portion concave; posterior aspect broadly in an inverted Y- or U. Metanotum narrow, with blunt median tumosity Propodeum with dorsal face flat, rectangular, steeply sloping posterad, separated from rectangular declivitous face by transverse carina. As seen laterally, dorsal and declivitous faces of propodeum meeting at obtuse angle; declivity marginate on each side.
Petiole clavate, with anterior peduncle and long, low, rounded node, usually bent slightly downward near base of posterior peduncle; spiracles papillose and prominent. Postpetiole broader than long in dorsal view and slightly broader posteriorly than anterad and broader than petiole; rounded above, sternum with shallow depression; attached to gaster by its full width. Gaster with first segment occupying most of its length; four visible apical segments subequal in length. Genital capsule slender; parameres slightly broadened, bluntly rounded and curved mesad at apices, but tapered to a blunt end as seen laterally; vol- sellae sock-shaped, as usual in MyrmicinaeHNS; pygidium and subgenital segment unremarkable, with moderately narrowly rounded apical margins.
Legs slender, tibiae of middle and hind pairs without apical spurs; tarsal claws slender and simple. Wings brownish, with opalescent bluish reflections. Forewing veined as in the gynes. Cross vein m-cu absent, present as a spur from M, or as a complete crossvein. Hind wing with only two longitudinal tubular veins issuing from median cell (apical abscissa of R and cu), with the tip of Sc branching off from fused Sc + R (Rf 1 lacking). Anal loop (A + Cu-a) short, without a spur of A, but as a folded line instead; 5 - 9 submedian hamuli.
Larva (after Wheeler & Wheeler, 1954): Moderately stout; thorax and first two abdominal segments not constricted to form a long " neck ". Of the two types of denticulate hairs, the larger one has a fine, tapered, not hook-liked apex.
1. Occipital margin of head rounded, forming a continuous or nearly continuous raised crest .......... 2
- Occipital margin of head trapezoidal or subrect- angular, not forming a continuous crest ........... 3
2. In full-face view, crest continuous around posterior part of vertex and separated from median convexity of vertex by a broad, uninterrupted sulcus parallel to the crest .................... B. militarisHNS
3. Mandible subtriangular, strongly bent ventrally and with the outer borders straight basally; anepisternum deeply depressed ........................... ........................................................ B. scambognathusHNS
- Mandible triangular, not strongly bent ventrally, outer borders usually convex basally; mesopleura at the same level as the surrounding surface ..... 4 4. Head nearly as broad as long with the occipital lobes rounded; in frontal view, intermandibular space much shorter than the half length of mandibles; gaster with few specialized hairs longer than the basal pilosity .................................... 5
- Head distinctly longer than broad with the occipital lobes angulated; in frontal view, intermandibular space broad, with about half length of the mandibles; gaster densely covered with specialized hairs longer than the basal pilosity ............ 6
5. Petiolar node and postpetiole totally covered with dense pilosity; petiolar node well developed and subrectangular in dorsal view; ventral carina of petiole with many developed teeth of different shapes ..................................................... B. conjugansHNS
- Petiolar node and postpetiole weakly covered with pilosity; petiolar node subcylindrical in dorsal view to almost obsolete; ventral carina of petiole with a single developed tooth at the anterior portion of peduncle .......................... B. convexicepsHNS
6. Basal portion of mandibles with dense pilosity formed by whitish squamiform hairs; ventral carina of petiole with a short edge at the anterior portion of peduncle ............................ B. singularisHNS
- Basal portion of mandibles smooth and shiny; ventral carina of petiole with a well developed edge at the anterior portion of peduncle, followed by smaller denticles of different shapes ...... B. manniHNS