Stigmatomma besucheti

Published records of other organisms collected by Schauenberg on La Digue island on 28.Jan.1975 indicate the type series of S. besucheti was probably extracted from soil samples submitted to Berlese funnels (Mahunka 1978b, Mahunka 1978a).

Identification
Esteves and Fisher (2016) - In the Malagasy bioregion, Stigmatomma besucheti is unique and easily recognized by: reduced number of antennomeres, palpal formula, head sculpture, absence of any enlarged process ressembling a spur on the apex of the mesotibia, petiolar proprioceptor zone reduced to a small concavity, and small body size. Further, it does not occur in sympatry with any other congener.

With characters of the besucheti species-group and the following characters (asterisks flag unique characters within Stigmatomma in the Malagasy bioregion):

1. Integument yellow; small-sized ant (HL: 0.38-0.40, WL: 0.41-0.43).

2. Pairs of teeth of mandible’s baso-masticatory margin the same size along mandible’s basoapical axis.

3. * Tongue-like setae medially inserted on mandible’s baso-mastigatory margin.

4. * Dorsal face of the head densely taeniate-catenate.

5. Genal teeth absent.

6. * Palpal formula 2:2.

7. Dorsal face of mesosoma and lateral face of propotum foveolate; declivitous face of propodeum smooth; lateral face of propodeum mostly smooth.

8. Mesepisternum divided by a sulcus into anepisternum and katepisternum.

9. * Mesotibial spur absent.

10. * Apex of mesotibial inner face bearing a deep fovea; absence of any enlarged process ressembling a spur.

11. Slit-like sulcus present on the anterior face of mesobasitarsus, with apical end projected laterally.

12. Anterior face of posterior metatibial spur glabrous; posterior face with antler-like microtrichia dorsoapically.

13. Brush of few stout, paddle-like setae present on the baso-inner face of metabasitarsus.

14. Absence of fenestra on lateral face of subpetiolar process.

15. Subpetiolar process fin-like: half of its ventral margin obtusely angled.

16. Presence of 5-6 stout spiniform setae on apex of hypopygium.

Distribution based on Regional Taxon Lists
Malagasy Region: Seychelles.

Nomenclature

 *  besucheti. Amblyopone besucheti Baroni Urbani, 1978a: 49, figs. 15, 16 (w.) SEYCHELLES IS. Combination in Stigmatomma: Yoshimura & Fisher, 2012: 19.

Esteves and Fisher (2016) - Two specimens from Singapore (a worker and a queen; CASENT0172194 and CASENT0195513, respectively) share remarkable similarities with the type specimens (e.g., antennomeres, general body shape and size, sculpture on the head, lack of any spiniform process on the mesotibial inner apex). However, those specimens differ in the following characters (corresponding characters of type specimens are presented within parentheses):

1. Three mandibular pairs of teeth (four pairs of teeth).

2. The posterior-most pair of long filiform setae on the clypeus of the Singapore specimens is much longer.

3. Supraclypeal area as a longer oblong depression (small oblong depression).

4. Anterior face of posterior metatibial spur glabrous; posterior face glabrous (anterior face glabrous; posterior face with antler-like microtrichia dorsoapically).

Despite these differences, we did not examine enough specimens of each form to evaluate character variation, and therefore cannot affirm they are different species. Also, while it seems improbable that a specialized predator would become an exotic species, it is noteworthy that: (1) the putative prey of Stigmatomma besucheti (i.e., geophilomorph centipedes) are widespread around the world and a major component of soil ecosystems (Bonato et al. 2013); and (2) global trade is known to profoundly influence the movement of species around the world (McNeely et al. 2001), and plant seeds and other organisms were inadvertently dispersed in the soil used as ballast in early shipping (McNeely et al. 2001). The Seychelles have historically occupied a strategic position along Indian Ocean trade routes, providing coaling/fuelling stations for ships bringing goods from the East to Europe and North America (Ofcansky 1995). In addition to the specimens collected in Singapore, there is single specimen collected in Sabah (Borneo; CASENT0235146) that resembles Stigmatomma besucheti in the number of antennomeres, head sculpture, mandible and clypeal configuration, size, and color, but differs in some significant characters of the petiole. Compared to S. besucheti, the anteroventral margin of petiolar tergite anterior dorso-latero-ventral carina is much shorter, and the shape of the subpetiolar process is different. Unfortunately, specimen CASENT0235146 was previously submitted to DNA extraction (Ward and Fisher 2016), and is too fragile for a thorough examination.

Worker
Esteves and Fisher (2016) - HL: 0.38-0.40; HW: 0.28-0.29; HW2: 0.26-0.27; SL: 0.18-0.19; ML: 0.20-0.22; WL: 0.41-0.43; PPW: 0.15-0.16; PtL: 0.14-0.15; PtW: 0.16-0.16; CI: 71.36-73.54; SI: 46.04-48.68; MI: 52.26-55.45; PtI: 90.00-92.50.

Mandibular baso-masticatory margin skirted dorsally by row of filiform setae; medially, by flexuous tongue-like setae; ventrally, by flexuous filiform setae, grading into flexuous tongue-like setae apically. Mandibular dentition arrangement, from base to apex: two single teeth (same size of teeth arranged in pairs); four pairs of teeth (each pair with same dimensions, fused basally); single preapical tooth; apical tooth. Pair of teeth with similar dimensions along mandible's basoapical axis. Anterior clypeal margin with three cuticular processes arranged in a single row, armed anteriorly with asymmetrical mucronate dentiform seta; followed laterally by a notch on the anterior clypeal margin. Most lateral portion of anterior clypeal margin armed with row of conical setae arising from flat cuticle (or from reduced tubercle-like cuticular processes), decreasing in size laterad. Clypeal cuticular processes with approximately same length of associated dentiform setae. Long filiform setae pair on clypeal median area, posterior to central-most pair of cuticular processes on clypeal anterior margin. Shorter filiform pair of setae on clypeal median area, between longer pair of setae and frontal lobes. Median area of clypeus extending posteriorly between antennal sockets as narrow longitudinal strip; frontoclypeal sulcus acute. Supraclypeal area as small oblong depression. Ten antennomeres. Genal teeth absent. Compound eyes absent. Palpal formula: 2:2 (two maxillary, two labial).

Mesosoma: In dorsal view, mesonotum somewhat expanded laterally. Metanotal suture absent. Sulcus dividing mesepisternum into anepisternum and katepisternum; dorsoposterior corner of katepisternum not rounded. Metathoracic spiracle slit-like, surrounded by cuticular swell, projected posteriorly, inserted in a concavity. Propodeal spiracle round, surrounded by a cuticular swell. Propodeal declivitous face slightly concave.

Legs: Absence of lamella on basoventral margin of calcar of strigil. Calcar of strigil anterior face with squamiform microtrichia basally; posterior face mostly glabrous. Multiple paddle-like setae on anteroventral face of protibial apex, next to calcar of strigil. Multiple paddle-like setae on anterior face of probasitarsus; row of stout setae along posterior face, next to comb of strigil. Mesotibial spur absent; apex of mesotibial inner face with deep fovea. Slit-like longitudinal sulcus on anterodorsal face of mesobasitarsus, with apical end projected laterally. Two metatibial spurs; anterior spur simple with lanceolate microtrichia; posterior spur pectinate. Anterior face of posterior metatibial spur glabrous; posterior face with antler-like microtrichia dorsoapically. Dorsal face of metabasitarsus with two parallel carinae with convergent apexes. Brush of few stout paddle-like setae on baso-inner face of metabasitarsus). Arolium on pro-, meso-, and metapretarsus.

Metasoma: Petiole sessile. Ventroanterior margin of petiolar tergite anterior dorso-lateroventral carina (Ward 1990) 2x the size of anterior margin of subpetiolar process, in lateral view. Subpetiolar process with obtuse angle at midpoint of its ventral margin (fin-like). Absence of fenestra on lateral face of subpetiolar process. Petiolar proprioceptor zone reduced to small round concavity bearing few sensilla. Prora present. Smooth sulcus between pretergite and postergite of abdominal segment III; weakly scrobiculate sulci between presclerites and postsclerites of abdominal segment IV. Five to six stout spiniform setae on apex of hypopygium.

Sculpture: Mandibular dorsal face costate-slightly catenate basally, grading into costate apically except for smooth apical portion. Clypeal median area smooth, grading into costate to rugose laterally. Supraclypeal area smooth. Head, in dorsal view, taeniate-catenate; area posterior to tentorial pit plicate. Labrum weakly imbricate. Mesosoma in dorsal view and lateral face of pronotum foveolate. Anepisternum smooth; katepisternum mostly imbricate; metapleuron costate posteriorly; lateral face of propodeum smooth, grading into imbricate posteroventrally; declivitous face of propodeum smooth. Petiolar tergite imbricate ventroanteriorly, grading into weakly and scarcely foveate dorsally and posteriorly. Petiolar laterotergite imbricate; petiolar poststernite mostly areolate, grading into smooth ventrally. Most of gaster weakly foveolate.

Pilosity and color: Suberect pilosity on head, dorsal face of mesosoma, lateral face of pronotum, petiolar tergite, and abdominal segments III, IV, V, and VI. Legs densely covered by subdecumbent pilosity. Suberect pilosity on anterior half of petiolar poststernite. Longer pilosity on abdominal segment VII. Body color yellow.

Type Material
Holotype (worker, CASENT0101816): Seychelles: Ile de la Digue, 28.Jan.1975, P. Schauenberg leg. Paratypes: 9 workers; same data as holotype. 

References based on Global Ant Biodiversity Informatics

 * Baroni Urbani C. 1978. Contributo alla conoscenza del genere Amblyopone Erichson (Hymenoptera: Formicidae). Mitt. Schweiz. Entomol. Ges. 51: 39-51.
 * Dorow, Wolfgang H. O. 1995. Review and Bibliography of the ants of the Seychelles (Hymenoptera: Formicidae). J. Afr. Zool. 110:73-96
 * Dorow, Wolfgang H.O. 1996. Review and bibliography of the ants of the Seychelles. Journal of African Zoology 110(2): 73-95.
 * Fisher B. L. 1997. Biogeography and ecology of the ant fauna of Madagascar (Hymenoptera: Formicidae). Journal of Natural History 31: 269-302.