Basiceros convexiceps ( Mayr 1887 )

Probst, Rodolfo Da Silva & Brandão, Carlos Roberto Ferreira, 2022, A taxonomic revision of the dirt ants, Basiceros Schulz, 1906 (Hymenoptera, Formicidae), Zootaxa 5149 (1), pp. 1-75 : 23-28

Basiceros convexiceps ( Mayr 1887)

( Figs 8–10 , 30 )

Ceratobasis convexiceps Mayr 1887: 581 (worker). Brazil: Santa Catarina.

Borgmeier 1937: 245, Figs 30 –33 (worker, gyne, larva diagnosis).

Emery 1924: Plate 6, Fig 9 (male diagnosis, figure corresponds to forewing).

Combination in Basiceros: Emery 1924: 328 .

Basiceros squamifer Borgmeier 1937: 245 . Brazil: Rio de Janeiro, Jussaral (next to Angra dos Reis).

Basiceros squamifer as junior synonym of Basiceros convexiceps: Brown & Kempf 1960: 172 .

Type material. BRAZIL: Santa Catarina: no locality, no date, Hecko (?) col., (one worker — holotype of Ceratobasis convexiceps ) [ NHMW] (examined) . Rio de Janeiro: Angra dos Reis, Jussaral , 30.x.1935, M. S. Lopes & H. Lent cols. (60 workers, three gynes and larvae of different instars—cotypes/ syntypes of Basiceros squamifer ), n. 5510— Coleção Borgmeier (41 workers, two gynes—cotypes/ syntypes of Basiceros squamifer ) [ MZSP] ; same data (three workers —cotypes/ syntypes of Basiceros squamifer ) [ IFLM] ; same data, MZC-Cotype n. 28512/ Cotype n. 5540 (three workers and two gynes—cotypes/ syntypes of Basiceros squamifer ) [ MCZ]; USNM-Cotype n. 58766 (two workers —cotypes/ syntypes of Basiceros squamifer ) [ USNM], USNM-Cotype n. 5561 (one worker —cotype/ syntype of Basiceros squamifer ) [ GUPC] (examined) ; same data (one worker —cotype/ syntype of Basiceros squamifer ) [MNHN-Muséum National d’Histoire Naturelle ] (not examined) ; same data (one worker —cotype/ syntype of Basiceros squamifer ) [MSNG-Museo Civico di Storia Naturale ‘ Giacomo Doria’ ] (not examined); other type material (9 workers) not located and not examined .

Diagnosis. Color reddish, ferruginous. Head trapezoidal; vertexal margin continuously convex in both directions, except for the presence of a median longitudinal groove. Subpetiolar process composed of single projection, anteroventral to the peduncle and curved anteriorly—posterior margin rarely presenting a small dentiform projection.

Description. Worker (n=3). HL 1.25–1.28, HL2 1.25–1.30, HW1 1.28–1.31, MdL 0.72–0.78, SL1 0.84–0.89, SL2 0.89–0.94, PDL 0.11–0.13, A3L 0.03–0.05, AFL 0.36–0.38, FuL 0.97–1.00, EL 0.16–0.17, EW 0.14–0.16, ML 1.69–1.72, MfL 1.33–1.34, MtL 1.00–1.06, PH 0.38, PL 0.77–.081, PW 0.36–0.38, PPL 0.47–0.50, PPW 0.53–0.61, GL 1.59–1.63, GW 1.13–1.19, TL 6.58–6.61, CI 100–105, CS 1.27–1.28, MCI 56–62, SI 69–73, ESI 17–19, SAI2 247–252, EI1 0.23–0.26, MFI 95–97, PTI 204–216.

Color reddish, ferruginous; appendages slightly lighter, reddish-brown. Mandibles covered with tiny piligerous punctuations, apex with short yellowish setae; interdental setae present, yellowish and filiform, subequal to teeth length. Basimandibular seta present, narrow and erect, slightly clavate. Suberect and clavate hair on the dorsomedial region of each stipe. Frontoclypeal margin covered by spaced piligerous punctuations; lateral limits of clypeus with decumbent, short and squamiform yellowish hairs. Head dorsum predominantly covered by coarse (foveate) piligerous punctuations; pilosity close to posterolateral region of head and vertexal margin composed of whitish to yellowish, short and subdecumbent squamiform hairs. Head lateral and vertexal margins covered by clavate yellowish hairs, erect to suberect in the following conformation: one hair above the eyes, at the anterior limit of the antennal scrobe; four hairs on the posterolateral margin, bordering the meeting of upper limit of scrobe and vertexal margin; a hair near the posterolateral corner of the head; four or five hairs on each side of the vertexal margin, separated by the median sulcus. A pair of yellowish hairs erect and clavate on the frontal region, close to the vertexal margin. Sides of head ventral margin covered by whitish and squamiform subdecumbent hairs; ventral head surface with suberect and subdecumbent curved filiform setae, length variable. Four to six long fine setae bordering the occipital carina. Yellowish to whitish subplumose hairs, usually subdecumbent, on the meso- and metasoma, in the following conformation: surrounding the anterolateral margin of pronotum; on the dorsum of mesonotum and propodeum; on the side of the sloping margin of propodeum; densely on the dorsum of petiolar and postpetiolar nodes; three pairs on each side of the anterolateral region of the postpetiolar sternite; on the anterolateral region of the procoxae and dorsum of meso- and metacoxae; on legs, from trochanters to basitarsus dorsum. Clavate hairs in the following conformation: one pair, erect, present on the dorsum of mesonotum, close to the promesonotal suture; erect to suberect, close to the margins of the sternites and gastral tergites. Mesosternum shelf (surrounded by epicnemial carina) with short, filiform setae along its length. Long, filiform setae present in the anterior portion of procoxa and median portion of the first gastral sternite. Thick and suberect setae present from the ventral margin of basitarsus to the apex of the apical tarsomere. Antennae pilosity: dorsal surface of scape primarily covered by short subdecumbent and squamiform hairs; external margin of scape with long and erect hairs, clavate on apical half; funiculus densely covered with short appressed yellowish setae; ventral margin of scape with longitudinal rows of medium setae, curved and subdecumbent. Remaining of integument with coarse piligerous punctuations.

Body mostly smooth and shiny on glabrous regions. Mandibles and clypeus dorsa sparsely covered by punctuations. Anteroventral portion of mandibles and ventral margin of scapes finely alveolate. Head punctuate-foveate, posterolateral surface of antennal scrobe punctuate-rugose. Pronotum sparsely foveate. Dorsum of mesonotum, anterodorsal region of the propodeum, dorsal surface of the meso- and metacoxae, and dorsum of the petiolar postpetiole nodes punctuate-rugose. Mesopleuron and lateral of the propodeum smooth and shiny or subopaque. Surface of propodeal declivity punctuate-rugose. Gaster densely punctuate-reticulate; tergite surface of abdominal segments V, VI, and VII finely and densely punctuate, slightly opaque, tergal margins smooth and shiny; more sparse sculpture in the first gastral sternite, especially in the longitudinal axis of median region. Antennal scapes smooth or finely rugulose, usually shiny. Funiculi densely and finely punctuate, usually opaque. Legs smooth or superficially rugose; procoxae punctuate-foveate.

Head trapezoidal, narrower anteriorly. Vertexal margin continuously convex in both directions, except for the presence of a shallow longitudinal sulcus that extends downwards into the posterofrontal region of the head; posterolateral angles rounded. Cervical margin carinate. Stipes subrectangular. Labrum cuneiform, long; distal margin bilobed, lobes tapered and separated by narrow cleft. Mandibles triangular; in full-face view, lateral margins of mandibles slightly concave in its apical half; basal angle usually indented, followed by 12–13 triangular teeth on the masticatory margin; in lateral view, mandibular apex slightly curved ventrally. Clypeomandibular space semielliptical. Clypeus anteriorly lamellated; anterolateral portion gently convex; anterior margin subrectilinear. Scape with obtuse basal angle ranging from slightly convex to slightly concave before the beginning of a translucent and crenulate lamellar portion. Antennal fossa deeply impressed. Antennal scrobe comparatively deep in its anterior half.

In lateral view, mesosoma profile with promesonotal complex subglobular. In dorsal view, promesonotal suture practically indistinct; metanotal suture broad and deeply inserted, longitudinally costulate. Mesopleuron anteriorly marginate, interrupted at the meeting with a conspicuous epicnemial fossa. In dorsal view, propodeum subrectangular. In lateral view, anterior portion of propodeum slightly oblique posteriorly, abruptly followed by the sloping face. Propodeal declivity laterally carinate and with transverse carina connecting to short, sharp and triangular propodeal projections. Opening of the propodeal spiracle rounded. Metapleural gland bulla protruding, prominent; opening transversal and covered by cuticular lamella. Petiolar peduncle longitudinally carinate on its dorsal surface. In dorsal view, propodeal spiracle weakly projected laterally. In lateral view, petiolar node with truncated anterior face, sloping posterodorsally; postpetiole slightly longer than the petiolar node. Subpetiolar process consisting of an anterior process curved anteriorly. In dorsal view, petiolar node longitudinally elliptical; postpetiole (excluding pilosity) slightly wider than long, posterior margin convex and widely inserted into the anterior concavity of gaster. Calcar of strigil pectinate. Pro-, meso- and metabasitarsi longer than the sum of other tarsomeres. Tarsal claws simple.

Gyne (n=2). HL 1.34–1.36, HL2 1.31–1.34, HW1 1.34–1.41, MdL 0.80–0.81, SL1 0.94–1.00, SL2 0.91–0.97, PDL 0.13, A3L 0.03–0.05, AFL 0.39, FuL 1.00–1.08, EL 0.25–0.30, EW 0.22–0.25, LOD 0.09, MOD 0.09–0.13, OOD 0.41–0.44, ML 2.03, MSL 1.00–1.06, MSW 1.03, MLL 0.34–0.36, MLW 0.56–0.59, MfL 1.34–1.38, MtL 1.08–1.09, PH 0.44, PL 0.97, PW 0.47, PPL 0.56, PPW 0.72, GL 1.94, GW 1.41–1.44, TL 7.64–7.67, CI 100–103, CS 1.34–1.38, MCI 59–59, SI 67–68, ESI 25–32, SAI2 232–248, EI1 0.34–0.41, MTI 97–103, MLI 163–165, MFI 97–104, PTI 221.

Color and sculpture similar to worker; body size ranging from equal to slightly larger. Cephalic dorsum with three ocelli: median ocelli inserted slightly below and lateral ocelli inserted just above a pair of clavated and erect hairs. Head pilosity as in workers. Pilosity of the anterolateral pronotal margin denser and longer than in workers. Whitish subdecumbent and squamiform hairs near the humeral angles and surrounding the posterior limit of pronotum; short and sparse on the dorsum of mesoscutum; on the scutoscutellar sulcus; on the dorsum of mesoscutellum; a pair on the metanotal flange, suberect. Whitish erect to suberect and clavate hairs on each side of pronotum, one pair close to pronotal suture; a pair on the metanotal flange; narrower and present as eight pairs on mesoscutum dorsum; one pair on each parapsis; one on each axilla, laterally; one on the lateral margin of mesoscutellum. Hairs on the gaster more abundant than on workers. In dorsal view, mesoscutum anteriorly rounded, slightly cuneiform, posterior margin slightly convex, medially in the meeting with the scutoscutellar suture; notauli indistinct; parapsidal lines narrow and inconspicuous, involved by the sculpture; parapsis shallow, rudimentary; tegulae narrow, apical margin rounded. Pre-scutellum narrow; axillae projected posteriorly, rounded and slightly depressed. Scutoscutellar suture well-defined. Mesoscutellum transversely subrectangular, posterior limit concave. Dorsal face of propodeum strongly inclined. In lateral view, anapleural sulcus broader anteriorly at the connection with the epicnemial fossa, narrowing posteriorly. Median region of first gastral sternite slightly projected on its basal half. Wing venation unknown (only dealate gynes were examined).

Male. Only known from diagnosis ( Emery 1924), translated below: “Epistoma (= clypeus) projected anteriorly. Frontal margin (= frontal carina) short, auricular. Mandibles long, advancing beyond the clypeus and disc-shaped, lateral margin (= external margin) rounded and medial margin (= masticatory margin) straight, armed with numerous sharp, serrated teeth. Antennae long, 1st funicular segment very short. (In the forewing) Portion of the wing anterior to the pterostigma large and well developed, radial (=1st marginal) cell open; cubital cell Solenopsis - type; inconstant discal cell”. According to Emery’s description, the forewing fits in part the type 1 adopted for the present work.

Larva (first description, based on several specimens from the type-series of B. squamifer ). Approximate length through spiracles: 4.4 mm ( Borgmeier 1937, 246: “larger larvae measure about 4 mm ”); profile pogonomyrmecoid: larger diameter near the middle of the abdominal region, thorax markedly narrower than the abdominal region, forming a neck; curved ventrally. Anus ventral; anal opening moderately convex, anal lobe present. Spiracles small. Integument of the ventral region densely covered by spinules arranged in transverse rows. Due to the state of the larvae, pilosity was lost in most of the body surface. Still, it was possible to notice sparse broken setae on the head, alveolar and with articular membrane, and on the ventral margin of the thorax (about 0.10–0.20 mm), flexible and denticulate ( Borgmeier 1937, 246: “{the larvae} have a fine erect pilosity and in each segment there is a transverse row of isolated, longer and anteriorly curved hairs”). Cranium subhexagonal, median impression present, antennae very small and inserted in the anterior half of the cephalic capsule. Clypeus protruding. Labrum strongly bilobed; ventral surface spinulose. Mandibles pogonomyrmecoid, long and narrow, medially curved; apical tooth curved and with a rounded apex; two protruding teeth projecting into the masticatory margin. Maxillae parabolic, apex spinulose; maxillary palps and galeae digitiform, subequal, elongated and narrow. Labium covered by subtransverse rows of spinules; spinules developed, capillary (about 0.02 mm) and densely covering the labium surface; labial palp papillary; opening of sericeous gland transverse. Hypopharynx densely spinulose.

Etymology. From Latin “ convexus ”, arched, curved; “ ceps ”, combinative form of “ caput ”, head. Mayr probably named this species based on the shape of the vertexal and occipital margins, which, except for a shallow groove in the median region of the vertexal margin, are continuously and uniformly convex in both directions. Also from Latin “ squama ”, scale; “ fer ”, radical of “ ferre ”, infinitive present of the irregular verb “ ferȏ ”, to carry, to bring. Borgmeier probably named the junior synonym B. squamifer based on the squamiform pilosity. It is interesting to mention that the term “ squama ”—possibly originated from the Latin “ squalidus ” (rough, coated with dirt, dirty), could also be associated with the epithet of this species.

Comments. Brown & Kempf (1960) refer to this species as having the most generalized morphology within the then Basicerotini tribe, arguing that the group’s adaptive radiation probably came from an ancestral stock similar to B. convexiceps .

Based on all the specimens available for examination for the present study, the morphological uniformity presented by this taxon is remarkable. Considering the current geographical distribution of B. convexiceps , there is practically no variation between specimens from different locations, except for minor differences in cephalic rugosity and pilosity—the latter probably associated with abrasion. In his description of B. squamifer, Borgmeier (1937, p. 245) distinguishes it from B. convexiceps mainly by the different postpetiolar proportions. According to Mayr (1887: 581) “ der zweite Knoten ist kürzer als hinten breit, aber so lang als vorne breit ” (the second node [=postpetiole] is shorter than wide posteriorly, but as long as wide anteriorly) and Borgmeier cites it as distinctly longer than wide for B. squamifer . Brown & Kempf (1960), when examining the type-series of both species, claimed that Mayr’s original description failed to approximate the correct proportions of the postpetiole and synonymized B. squamifer under B. convexiceps .

The male described by Emery (1924) could not be located. Several attempts to examine that specimen were made, initially by contacting the NHMW, since the type-material of B. convexiceps collected by Dr. Gustav Mayr is supposedly deposited in that Institution. Additionally, the online database of the MHNG—where Emery’s collection is located—does not inform that male specimen to be deposited there and our correspondence with the MHNG curator has yet to be returned. Other communications made with different European Museums also resulted in none locating that specimen.

The description of the larvae is based on several specimens found with the type-series material of B. squamifer . The original vial was located in the wet (alcohol) collection of the Hymenoptera Laboratory at the MZSP, along with Borgmeier’s original labels with the same collection codes—including a label citing the microenvironment in which the specimens were collected. Although sample conservation was not ideal, one of the immatures was cleaned and submitted to the SEM. In addition, the vial contained fourteen workers; this material has been sorted, pin mounted, and incorporated into the MZSP collection.

Borgmeier (1937: 246) mentions that the description of B. squamifer was based on 60 workers and three wingless gynes, all collected in the same nest. However, relying on the material from the original collection, 49 workers deposited in different institutions were examined. One worker deposited at the MNHN and another one deposited at the Museo Civico di Storia Naturale “Giacomo Doria” (MSNG) were not examined, and it was not possible to locate the other nine workers mentioned by Borgmeier (1937). Considering the material available, the worker in the best state of conservation will be designated as the lectotype, aiming for the nomenclatural stability of the group.

In the present study, the worker deposited at the NHMW and examined by stacked macrophotographs is considered the holotype described by Dr. Mayr, although AntWeb treats the same specimen as a syntype of B. convexiceps . However, Mayr mentioned in his original description (1887) the monotypic status of B. convexiceps , which reinforces that specimen as being the holotype.

Two workers collected in Blumenau and deposited at the NHMB lack any mention of collection date, with labels only referring to the collector (spelling refers to “Müller”). This material was not mentioned in any publication referring to Basiceros , possibly due to difficulty obtaining material from the NHMB. Considering the age and calligraphy of the labels and comparing them with other ants collected in Santa Catarina, both by William Müller and Dr. Arth. Müller, these two workers were probably collected by the latter. It is interesting to mention that there is a second label (in German) on those specimens. The label data suggest that specimens were deposited in Dr. Félix Santschi’s collection during the time Dr. Santschi was established in Tunisia —more precisely in the city of Kairouan.

Mariano & Delabie (2013) studied the karyotype of two populations of B. convexiceps (one in Bahia and one in Minas Gerais) and registered for both 2n = 20, with meta and submetacentric chromosomes.

Distribution. This species is restricted to areas of the Brazilian Atlantic Forest biome, with records from the State of Santa Catarina to Bahia. Interestingly, it has not yet been collected in the State of Espírito Santo.

Natural history. Virtually nothing is known about the natural history of this species, and few are the collection events in which this species was found. For example, considering the entire length covered by the BIOTA Project, spanning the whole distribution of the Atlantic Forest and hundreds of 1m 2 leaf litter samples, only four specimens were collected: one in the State of Santa Catarina, one in Paraná, and two in São Paulo. According to field notes from Borgmeier , the nest series from Jussaral (60 workers and three gynes) was collected from a wide, rotted trunk, under the bark and inside it. The presence of three wingless gynes suggests that the colony was polygynic ( Borgmeier, 1937). Some specimens were collected from litter samples, indicating that B. convexiceps also nests or forages in the leaf litter.

Material examined. BRAZIL: Bahia: Itororó , 14°57’81”S 40°02’33”W, 08.viii.2000, J. R. M. dos Santos col. (1 worker) [ CEPEC] ; Minas Gerais: Viçosa, Mata do Paraíso , 20°45’S 42°52’W, 13.xi.2000, I. C. Nascimento col. (2 workers) [ CEPEC], 20°48’S 42°51’W, 12.ii.2015, J. Chaul, A. P. Alves cols. (1 worker) [ MZSP] ; Paraná: Morretes, Parque Estadual do Pau-Ôco , 25°34’33.5 “S 43°53’19.5” W, 06–11.v.2002, Silva, R. R. & Dietz, B. H. cols. col., (1 worker) [ MZSP] ; Santa Catarina: Blumenau, undated, Müller (?) Col. (2 workers) [ NHMB]; São Bento do Sul , APA Rio Vermelho , 26°21’51”S 49°16’16”W, 30.iii–04.iv.2001, Silva, RR & Eberhardt, F. cols., (1 worker) [ MZSP]; without locality, without date, Carlo Emery col., (1 worker), donation by W. M. Wheeler [ MCZ] ; São Paulo: Ilha dos Búzios, 19.x.1963, Expedition of the Department of Zoology col., N. 2804 (1 gyne), n. 2835 (1 worker) [ MZSP]; Picinguaba, Parque Estadual da Serra do Mar , 23°20’10”S 44°50’15.3” W, 30.ii–04.iv.2001, C. R . F. Brandão & Equip. cols. (2 workers) [ MZSP]; no date, no locality (1 gyne) [ USNM] .

Figures

FIGURE 8. Basiceros convexiceps, worker (MZSP, Brazil: São Paulo); A. full-face view, B. lateral view; C. dorsal view. Scale bars: A = 0.5 mm, B–C =1 mm.

FIGURE 9. Basiceros convexiceps, gyne (MZSP, Brazil: São Paulo). A. full-face view, B. lateral view; C. dorsal view. Scale bars: A = 0.5 mm, B–C =1 mm.

FIGURE 10. Basiceros convexiceps, larva (from type-series of Basiceros squamifer) (MZSP, Brazil: Rio de Janeiro) and male forewing diagram (adapted from Emery, 1924) (Brazil: Santa Catarina); A. Head in ventro-oblique view, B. head in oblique view, C. male forewing (black arrow highlights transversal 1m-cu vein), D. anus, E. thorax in lateroventral view, highlighting the spinose pilosity, F. lateral view. Scale bars: A, B–E = 0.1 mm; F = 0.5 mm.

FIGURE 30. Distribution map of Basiceros species from the singularis clade.