Basiceros Schulz 1906
Creators: name: Probst, Rodolfo Da Silva
name: Brandão, Carlos Roberto Ferreira
Publisher: name: Zenodo
Year: 2022
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Insecta
Hymenoptera
Formicidae
Basiceros

description: Basiceros Schulz 1906
Meranoplus (in part) Smith 1858: 195.
Ceratobasis Smith 1860: 78 (junior homonymous of Ceratobasis Lacordaire 1848: 362, Cerambycidae, Coleoptera).
Basiceros Schulz 1906: 156 (name replacing Ceratobasis; Meranoplus singularis, type species by monotypy).
Basiceros in Myrmicinae, Dacetini: Emery 1914: 42; Forel 1917: 246; Wheeler 1922: 666; Emery 1924: 327; Donisthorpe 1943: 627; Brown 1948: 102; Baroni Urbani & de Andrade 1994: 30; Baroni Urbani & de Andrade 2007: 81.
Basiceros in Myrmicinae, Basicerotini: Brown 1949: 87; Brown & Kempf, 1960: 171; Bolton 1994: 105; Bolton 1998: 67; Bolton 2003: 53, 183.
Basiceros in Myrmicinae, Attini: Ward et al. 2015: 17.
Wheeler & Wheeler 1955: 112–113 (larva description); Brown & Kempf 1960: 171–172 (description of the worker and gyne diagnosis); Brown 1974: 132 (worker, gyne, and larva diagnosis; male description; distribution and biology); Bolton 2003: 183–184 (taxonomic background).
Aspididris Weber 1950: 3 (A. militaris, type species by monotypy), junior synonym of Basiceros Schulz: Brown 1974: 132.
Creightonidris Brown 1949: 89 (C. scambognatha, type species by monotypy), junior synonym of Basiceros Schulz: Feitosa et al. 2007: 33.
Diagnosis: The workers and gynes of Basiceros are differentiated from the other members of the Basiceros -genus group by the combination of body size (the largest within this group), antennae with 12 segments, presence of hairs on the postpetiolar sternite, basimandibular seta, and body pilosity (usually composed of a double layer of specialized hairs). Males can be distinguished by the combination of the twisted antennae, mandible shape, petiole and postpetiole shape in dorsal view, pattern of wing venation, and mesopleuron sculpture. The most important morphological characters to distinguish between workers/gynes of different Basiceros species are the head and labrum shapes, mesosoma profile in lateral view, and the pattern of specialized pilosity. For males, head and mandible shape, mesosoma in anterior view, shape of petiolar node in lateral view, and mesopleuron sculpture are important.
Caste diagnosis. Worker. Comparatively medium-sized ants (TL: 4.5 to 8.7 mm). Color amber-yellow to black. Integument thick, usually densely sculptured: punctuate/foveate (or a combination of both) or rugose. Pilosity conspicuous and generally specialized; erect setae from sparse to abundant, usually clavate; subdecumbent pilosity sparse to abundant, squamiform, spatulate-clavate or plumose. Labrum shape variable, either long and cuneiform and bilobed apically or somewhat lunate with a rounded distal margin (see Probst et al. 2019, Figs 2–3), labral surfaces with specialized setae (probably with sensorial role) along its distal margin and sometimes in the ventral margin. Head trapezoidal, oblong or posteriorly disc-shaped; lateral and vertexal margins distinctly visible: rounded, angulate or as a continuously or medially emarginated crest along the posterior margin. Mandibles triangular or subtriangular, usually elongated; multidentate, with masticatory margin entirely opposite; apical portion straight to strongly curved ventrally; basal margin from slightly curved to conspicuously concave, clypeomandibular space absent to present in varying degrees (see Probst et al. 2019, Fig 4). Compound eyes relatively developed. Antennae with 12 segments; scape dorsoventrally flattened, with external margin forming biangulate basal lobe followed by a crenulated lamella; antennal club moderate to conspicuous, with last two funicular segments usually distinct. Mesosoma robust or elongate; in lateral view, promesonotum continuously convex to strongly projected caudad; metanotal suture present, broad. Dorsal margin of propodeum slightly sloping upwards at its posterior portion; slope margin from slightly to abruptly oblique. Propodeum armed with triangular or tapered projections, slightly lamelliform and connected by a transverse carina usually slightly curved upwards. Petiole pedunculate; dorsal margin with rounded, low or weakly bulged node; subpetiolar process with different configurations, from absent to multidentate.
Gyne. Similar to conspecific workers, with modifications peculiar to that caste. Ocelli present. In dorsal view, mesoscutum slightly elongated, anterior portion cuneiform; notauli inconspicuous to weakly marked; parapsides generally oval, shallow to deep impressed; parapsidal lines somewhat shiny and slightly conspicuous to obsolete, involved by integumental sculpture; scutoscutellar sulcus from strongly to lightly impressed; pre-scutellum narrow, central portion relatively indistinct; axillae projecting posteroventrally, curved and hook-shaped; mesoscutellum transversely subrectangular to ellipsoid, posteriorly inclined, posterior margin concave. Metanotum visible, slightly projected. Wings usually light brown; pterostigma present in the forewing, distinct and brown to dark brown. Forewing with longitudinal veins C (costa), Sc (subcosta)+R, M+Cu, 1A (anal), Rs+M, Rs (radial sector) and R1 (radius); the Sc+R vein extends from its posterior half to near the front of the pterostigma in tubular form; M+Cu with spectral basal portion and anterior half tubular; anal vein usually with anterior portion tubular; Cu usually tubular, extending posteriorly nebulously; radial sector with nebulous apical portion, not meeting R1; R1 usually reaching the most distal point of the wing margin; anterior portion of the radial sector varying in size. Vein M tubular and oblique, length variable; Rs+M straight or moderately curved, usually tubular, M (media) usually tubular in its anterior half, extending nebulously to the wing margin; Cu similar to M. Transverse veins: cu-a generally tubular, connecting the anal vein with M+Cu just after half of the anal vein, near or right after the branching point; 2r-rs tubular connecting the pterostigma near its median region to the radial sector; Rs connecting the Sc+R veins to the M and Rs+M veins and marking the breakpoint of the latter two, varied 1m-cu vein: absent as an appendage of the Rs+M vein or reaching Cu, closing the discal cell. Hindwing with longitudinal veins Sc+R, M+Cu and 1A; Sc+R briefly extends into a tubular shape after the point of connection with the M+Cu vein as the Sc+R1 vein and extends in the spectral shape to near the distal margin of the wing; anal vein usually tubular; Cu as a tubular appendage either partially or entirely spectral; Rs+M as short tubular appendix and other spectral length or absent; cu-a and 1r-rs+M transverse veins present: the first connecting the anal and M+Cu veins near the median portion of this first; the second connecting Sc+R and M+Cu near the distal portion of these veins. Five to eight submedian hamuli present.
Male. Known Basiceros males are slightly smaller than conspecific gynes. Dark in color, with lighter appendages, from brown to dark brown. Integument mostly punctuate, punctuate-reticulate or foveate; some portions subopaque and slightly granulate, like the appendages; rugulae present near the head vertex, behind the compound eyes and with variable presence on the interocular space; sparse rugulae in the posterior half of the mesonotum and on the propodeum sides; mesopleuron differentially shining: either just at the mesoanepisternum with rest of the mesopleuron granulate, or much of the mesoanepisternum plus part of the mesokatepisternum shiny. Pilosity largely fine, filiform; suberect to subdecumbent, from yellow to brown. Head with maximum width close to the eye insertion; vertexal margin convex; cephalic capsule projected posteriorly, forming a variable conspicuous neck; occipital margin lamelliform and longitudinally costulate, varying in relation to the shape of the head (piriform or subpiriform). Compound eyes convex and prominent, ocelli protruding forming a cephalic crest in different degrees. Mandibles developed, triangular; external margins convex, curving apically; masticatory margins with 9–14 subtriangular teeth; basal margins with morphology similar to that of conspecific females, more or less concave with mandibles closed, leaving or not a clypeomandibular space. Clypeus ample, frontoclypeal portion slightly truncated or bulged, extending to the level of the frontal lobes; anterolateral portion depressed, concave; anterior margin lamellar, yellowish or slightly translucent, straight or medially concave medium, laterally rounded. Frontal area variably distinct, semicircular or transverse; slightly rugose or with a frons carina which extends more or less posteriorly towards the median ocellus. Frontal lobes salient, free margins sharply rounded in front; antennae inserted into their ventral face. Antennal scrobes deep and ellipsoid, delimited by a crenulate border and advancing to the lateral clypeal area. Postgenal carina continuous or almost continuous, irregular, extending from the posterolateral corner of the head to the mandibular insertion.Antennae long and filiform, with 13 segments. Scape short, about twice as long as wide; basal margin oblique and sharply rounded to the external margin, obtuse angle in the inner margin; apex truncated.Antennomeres 2 and 3 approximately half the length of scape; other funicular segments longer than wide; apical segment longer; antennal segments 8 and 9 slightly or conspicuously twisted, causing the antenna to appear to be twisted around its axis to varying degrees. Mesosoma robust, more or less elongated; pronotum anteriorly divided or not in two distinct portions; mesoscutum like conspecific gynes, presenting a longitudinal carina anteromedially, more or less distinct. Notauli complete, shallow or deeply impressed, extending after their converging point in variable fashion towards the scutoscutellar sulcus. Parapsides generally deeply marked, more or less oval; parapsidal lines shiny and distinct. Axillae projected as in the conspecific gynes, hook-shaped. Mesoscutellum in dorsal view shaped like an inverted “U”, posterior margin concave. Propodeum with posterior angles projected, projections either obtuse or slightly triangular, divided by strong transversal carina. Propodeal lobes auriculate. Metanotum narrow, medially projected. Petiole with morphology similar to conspecific females; petiolar spiracles projected laterad in the median portion of peduncle. Gaster in dorsal view with five visible segments. Genitalia (after Feitosa et al. 2007): genital capsule slender; parameres slightly enlarged, strongly rounded and with tips curved inward; in lateral view, abruptly narrowed toward the apex, volsella with the general pattern observed in Myrmicinae males; pygidium and subgenital segments with apical portion slightly narrow and rounded. Legs slender; calcar of strigil short and pectinate, present only on prolegs. Brownish wings; forewings with venation similar to conspecific gynes (varying regarding the length of transversal vein 1m-cu, that can be present as a short appendage on males and absent on gynes), with the following configuration: absent, obsolete (as a short appendage to Rs+M) or complete, closing the discal cell. Hindwings with tubular longitudinal veins Sc+R; M+Cu and 1A (anal), the former branching to short vein SC+R1 after the abscissa of Sc+R and M+Cu; Rs+M present as a short appendage after the abscissa of Sc+R and M+Cu. Anal vein short, apex slightly curved upwards, meeting cu-a; 4–8 submedian hamuli present.
Distribution. The genus has a restricted Neotropical distribution. The northernmost record comes from Honduras for B. manni, the southernmost record from the State of Rio Grande do Sul, Brazil, for B. disciger. In terms of elevation, collection information of examined specimens suggests that Basiceros might peak its abundance at low and medium elevation—supported by the absence of specimens in collections from high-elevation forests (> 1500m) and studies focusing on ant diversity along altitudinal gradients (e.g., Scott-Santos 2008).
Natural History. The scarce information from the literature (Weber 1950, Brown 1974, Hölldobler & Wilson, 1986) mention the dirt ants as being cryptic, with slow-moving habits, and presenting thanatosis when disturbed. Apparently, no recruitment has been recorded, and workers forage solitarily. As far as it is known, Basiceros do not excavate nests, and their colonies are usually found in leaf litter interstices, occupying soil cavities, hollow or rotten logs, seedpods, or preferably in areas with superficial root system or close to the base of large trees.
Little is known about its colonial structure (nests usually have ~50–100 individuals); collection records suggested that some species may be polygynic. Intercastes are reported for the first time in the present study. The unique morphology and the usually dense layer of soil and litter particles covering the integument of some species suggest that the dirt ants have a dietary preference—situation reinforced by an impressive morphological variation on the mouthparts across the genus (Probst et al. 2019).
Taxonomic synopsis
Basiceros browni Probst & Brandão sp. nov.
B. conjugans Brown 1974
B. convexiceps (Mayr 1887)
B. disciger (Mayr 1887)
B. manni Brown & Kempf 1960
B. militaris (Weber 1950)
B. redux (Donisthorpe 1939) = Octostruma reducta comb. n.
B. scambognathus (Brown 1949)
B. singularis (Smith 1858)
B. tumucumaquensis Probst & Brandão sp. nov.
Identification key for female castes of Basiceros
1. Head with round vertexal margin, either presenting a medially emarginate or continuous crest (Figs 11A and 17A)........ 2
- Vertexal margin continuously or moderately concave, crest absent (Fig 13A)...................................... 3
2. In full-face view, crest converging medially, emarginate. Sulcus interrupted by median vertexal convexity (South America, widely distributed) (Figs 11–12)................................................................. B. disciger
- In full-face view, vertexal crest continuous, separated by a broad uninterrupted sulcus (Central and N South America) (Figs 17–20)..................................................................................... B. militaris
3. Mandibles triangular, apices not abruptly curved ventrally, external margins convex in their basal portion (Figs 8A and 23A); basidorsal sulcus absent................................................................................ 5
- Mandibles subtriangular, apices strongly curved ventrally (Figs 21C, 27E), external margins subparallel in their basal portion; basidorsal sulcus present (Figs 21A, 26A–B)............................................................... 4
4. Head pilosity majorly composed of decumbent and squamiform hairs. Mandibles with basal portion covered with squamiform hairs; basal angle of mandibles right-angled, region indistinctly translucent. Surface of antennal scrobes completely sculptured, rugo-punctuate (South America, mainly Brazil) (Figs 21–22).................................... B. scambognathus
- Squamiform pilosity on head restricted to clypeal surface. Basal angle of mandibles broadly round, strongly translucent. Antennal scrobes matte, finely strigulate (N and NW Brazil) (Figs 26–27)...................... B. tumucumaquensis sp. nov.
5. In dorsal view, vertexal corners round; vertexal margin with short and clavate hairs. In full-face view, clypeomandibular space narrow, much shorter than half the maximum length of the clypeus (Fig 5A). Specialized pilosity on mesosoma and gaster sparse (Fig 5B)...................................................................................... 6
- In dorsal view, vertex corners angulate; vertexal margin with long and clubber hairs in its apical portion. In full-face view, clypeomandibular space wide, longer than half the maximum length of the clypeus (Fig 3A). Specialized pilosity on mesosoma and gaster dense (Fig 3B).............................................................................. 7
6. Pilosity on petiolar node, postpetiole, and lateral margin of propodeum dense, whitish, and squamiform. Subpetiolar process composed of denticles varying in shape and number (N South America) (Figs 5–6)....................... B. conjugans
- Pilosity on the petiolar node, postpetiole, and lateral margin of the propodeum sparse. Subpetiolar process consisting of a single ventral process located in the anterior portion of the peduncle (Brazilian Atlantic Forest, Santa Catarina to Bahia) (Figs 8–9)........................................................................................ B. convexiceps
7. In full face view, external margins of mandibles continuously curved from base to apex. Frontoclypeal surface smooth and shiny or slightly shagreened. Labrum lunate, anterior margin rounded (see Probst et al. 2019, Figs 2–3), lacking cleft..... 8
- In full face view, external margin of mandibles slightly sinuous. Frontoclypeal surface finely foveate-reticulate. Labrum acute and bilobed apically, lobes separated by very narrow cleft (Probst et al. 2019, Figs 2H and 4G) (Ecuador) (Figs 3–4)............................................................................................ B. browni sp. nov.
8. Mandible dorsum with dense squamiform hairs or irregular fovea. Clypeus with decumbent and squamiform pilosity. Distal margin of labrum convex (Probst et al. 2019, Fig 2F). Base of sternite of first gastral segment bearing median longitudinal elevation, generally carinate (Central and N South America, Trinidad and Tobago) (Figs 23–25)............ B. singularis
- Basal portion of mandibles smooth and shiny. Clypeus covered with piligerous punctures. Distal margin of labrum with medially protruding knob (Probst et al. 2019, Fig 2G). Base of sternite of first gastral segment lacking longitudinal carina or median elevation (Central America: Costa Rica to Honduras) (Figs 13–14)....................................... B. manni
Identification key for Basiceros males
1. 1m-cu partially closing the discal cell (Figs 1, 10C) (but see Notes below key)......................... B. convexiceps
- 1m-cu complete, always closing the discal cell (Figs 1C, 14E); clypeomandibular space wide (Fig 14D); pronotum divided into two levels, producing anteromedial concavity (Fig 24F)...................................................... 4
- 1m-cu absent or obsolete, discal cell absent (Fig 1A); clypeomandibular space narrow or absent (Fig 12D); pronotum undivided (but see Notes below key).............................................................................. 2
2. Mandibles sinuous or triangular; masticatory margins continuous; head piriform or subpiriform....................... 3
- Mandibles subtriangular, external margin strongly convex, apical tooth projected; head subhexagonal (Fig 22D–F)............................................................................................. B. scambognathus
3. Mesosoma shagreened, matte; mesopleuron costulate; antennal torsion exaggerated (Fig 28).. B. tumucumaquensis sp. nov.
- Mesosoma differently sculptured, mesopleuron partially smooth and shiny; antennal torsion modest................... 5
4. Mesokatepisternum covered with irregular rugulae; contrasting with the reticulate sculpture of mesoanepisternum; anterior face of pronotum slightly convex medially (Fig 24D–F)................................................ B. singularis
- Mesopleuron (mesokatepisternum + mesoanepisternum) reticulate; anterior face of pronotum conspicuously keeled (Fig 14D– F).......................................................................................... B. manni
5. Subpetiolar process present as anterior projection, curved anterad, followed by 1–4 teeth, a lamella, or both. Mesoanepisternum with at least half of its surface smooth and shiny, mesokatepisternum smooth and shiny on about half of its length (Fig 6D–F)......................................................................................... B. conjugans
- Subpetiolar process absent or present as minute spiniform projection; mesopleuron sculpture different................. 6
6. Subpetiolar process absent; mesoanepisternum smooth and shiny on about 2/3 of its length; mesokatepisternum fully punctuate-reticulate (Fig 12D–F)...................................................................... B. disciger
- Subpetiolar process present as an anterior spiniform projection, with apex slightly curved anteriorly; mesoanepisternum smooth and shiny on about half of its length; mesokatepisternum bright on posteromedial portion (Fig 18D–F)......... B. militaris
Notes: Overall, not many males were available for most Basiceros species; therefore, male key should be interpreted as tentative. It is likely that the male of Basiceros browni sp. nov. keys out on step 4, given the size of worker and mandibular morphology, similar to the other species in this dichotomy. Step 1 should be read with caution, as the male of B. convexiceps was not examined, and its inclusion in the key is supported only by the diagnosis and forewing illustration provided by Emery (1924). Basiceros conjugans males can sometimes present the transversal vein 1m-cu in one of the forewings, so that the discal cell can be present and absent on the same individual.
description: Published as part of Probst, Rodolfo Da Silva & Brandão, Carlos Roberto Ferreira, 2022, A taxonomic revision of the dirt ants, Basiceros Schulz, 1906 (Hymenoptera, Formicidae), pp. 1-75 in Zootaxa 5149 (1) on pages 10-13, DOI: 10.11646/zootaxa.5149.1.1, http://zenodo.org/record/6605961