Eusphinctus

Eusphinctus is a species-poor South East Asian genus with apparently small colonies. There are only two species of Eusphinctus, both quite similar, and Brown (1975: 75) allowed the possibility that specimens described as Eusphinctus taylori may be just small workers of Eusphinctus furcatus, but he decided not to synonymize them until more specimens are available. (Borowiec 2016)

Identification
Borowiec (2016) - Worker Eusphinctus workers belong to dorylines with conspicuous gastral constrictions visible between abdominal segments IV, V, and VI. This morphology is also seen in Aenictogiton, certain species of Leptanilloides, Sphinctomyrmex, and Zasphinctus. Eusphinctus is unique in the combination of propodeal spiracle situated low on the sclerite and propodeal lobes present, a large pygidium armed with modified setae, pronotomesopleural suture present, and cinctus of abdominal segment IV simple and not cross-ribbed. This genus is thus far known only from India, Bangladesh, Myanmar, and Thailand and the only lineage with gastral constriction that is currently known to overlap with it is Zasphinctus. In Zasphinctus the pronotomesopleural suture is fused, in Aenictogiton the propodeal spiracle is positioned high and there are no propodeal lobes, Leptanilloides has a reduced and unarmed pygidium, and the neotropical Sphinctomyrmex has 12-segmented antennae and the cinctus on abdominal segment IV smooth. The relative proportions of abdominal segments are also different, with segments IV, V, and VI being about equal in size in Sphinctomyrmex and Zasphinctus, while in Eusphinctus segment IV is the largest of the three.

Male The male of Eusphinctus can be recognized by a combination of 12-segmented antennae, pronounced propodeal lobes, narrow axial helcium, conspicuous constrictions present between abdominal segments IV, V, and VI, costal (C) cell present in the fore wing, submarginal cell closed by Rs·f2–3, R·f3 present past pterostigma, and marginal cell open. Abdominal sternite IX (subgenital plate) in Eusphinctus gradually tapers caudad and has simple, straight spines directed posteriorly. Sphinctomyrmex and Zasphinctus also have constrictions between abdominal segments IV, V, and VI but the former always has 13-segmented antennae and the latter lacks veins C and R·f3 in the fore wing.

Distribution
Indomalayan, known from India, Bangladesh, Myanmar, and Thailand.

Species richness
Species richness by country based on regional taxon lists (countries with darker colours are more species-rich). View Data



Biology
A. B. Soans and W. L. Brown collected two colonies of Eusphinctus furcatus in Kottiyoor, Kerala, India. One was located in leaf litter near a rotting log and the other one was found under a stone in a shaded creek bottom. There were about 50 workers in each of the observed nests, and one colony contained two ergatoid gynes (Brown 1975).

Nomenclature

 *  EUSPHINCTUS  [Dorlyinae]
 * Eusphinctus Emery, 1893a: cclxxv. Type-species: Eusphinctus furcatus, by monotypy.
 * Eusphinctus subgenus of Sphinctomyrmex: Emery, 1895k: 456.
 * Eusphinctus revived status as genus: Wheeler, W.M. 1918a: 219.
 * Eusphinctus junior synonym of Sphinctomyrmex: Brown, 1975: 31.
 * Eusphinctus as genus: Borowiec, 2016: 138.

Borowiec (2016) - Based on morphological and molecular evidence (Borowiec in prep.), I revive Eusphinctus from synonymy with Sphinctomyrmex. The taxonomic history of taxa classified under Sphinctomyrmex is somewhat complicated. Detailed discussions can be found in Wheeler (1918) and Brown (1975), and I only briefly recount the history of taxonomic changes to provide a background for an arrangement proposed here. The genus Sphinctomyrmex was established by Mayr (1866b) based on a single dealate gyne specimen from Brazil. Mayr emphasized the prominent constrictions between abdominal segments present in the specimen in the description, which gave inspiration for the name. Later, Emery (1893a) described a new genus from Myanmar, Eusphinctus, for an ant with similar constrictions. Other species from the Old World followed, described under either name. Wheeler in 1918 decided (after André 1905) to reserve Sphinctomyrmex for all New World forms and further split Eusphinctus into three subgenera, Eusphinctus s. str., Nothosphinctus, and Zasphinctus, according to various combinations of the gyne morphology, number of antennal segments (11 or 12), and presence or absence of eyes in the worker. Brown (1975) discussed the taxonomic history of the genus and all of Wheeler’s characters in detail. He pointed out that the characters used to differentiate these vary and the combinations enumerated by Wheeler do not hold as generic diagnoses with newly discovered species. Brown thus concluded that it was most sensible to synonymize all the genus-level names under Sphinctomyrmex until more evidence, particularly from male morphology, was gathered. However, he allowed for a possibility that two species, Eusphinctus furcatus and Eusphinctus taylori indeed deserved a separate generic status (Brown 1975).

Here I propose a new classification where all the New World species are retained in Sphinctomyrmex, while most of the described Old World forms are relegated to Zasphinctus. The two remaining above mentioned Old World species are separated from Zasphinctus as Eusphinctus. Molecular data shows that all three genera arose independently on the dorylomorph tree. Despite sharing characteristic gastral constrictions, these lineages are also discrete in worker and male morphology (see diagnosis above). Both morphology and molecules support the notion that abdominal constrictions have been independently derived several times in the Dorylinae: in Eusphinctus, Sphinctomyrmex, and Zasphinctus and also in Aenictogiton and some Leptanilloides.

Eusphinctus belongs to a clade that also includes Ooceraea and Syscia (Borowiec, in prep.). The members of this clade share the universal reduction in the number of antennal segments, from 12 to 11 or fewer in the worker caste and from 13 to 12 or fewer in males.

Worker
Borowiec (2016) - Head: Antennae with 11 segments. Apical antennal segment moderately enlarged, broader than and about equal in length to two preceding segments combined. Clypeus without cuticular apron. Lateroclypeal teeth present. Parafrontal ridges reduced. Torulo-posttorular complex vertical. Antennal scrobes absent. Labrum unknown. Proximal face of stipes unknown. Maxillary palps unknown. Labial palps unknown. Mandibles triangular, with teeth. Eyes present, composed of fewer than five ommatidia. Ocelli absent. Head capsule with differentiated vertical posterior surface above occipital foramen. Ventrolateral margins of head without lamella or ridge extending towards mandibles and beyond carina surrounding occipital foramen. Posterior head corners dorsolaterally immarginate. Carina surrounding occipital foramen ventrally present. Mesosoma: Pronotal flange separated from collar by distinct ridge. Promesonotal connection with suture completely fused. Pronotomesopleural suture visible, unfused up to notal surface. Mesometapleural groove weakly impressed. Transverse groove dividing mesopleuron present. Pleural endophragmal pit concavity present. Mesosoma dorsolaterally immarginate. Metanotal depression or groove on mesosoma absent. Propodeal spiracle situated low on sclerite. Propodeal declivity with distinct dorsal edge or margin and rectangular in posterior view. Metapleural gland without bulla visible through cuticle. Propodeal lobes present, well developed. Metasoma: Petiole anterodorsally immarginate, dorsolaterally immarginate, and laterally above spiracle marginate. Helcium in relation to tergosternal suture placed at posttergite and axial. Prora forming a simple U-shaped margin. Spiracle openings of abdominal segments IV–VI circular. Abdominal segment III anterodorsally immarginate and dorsolaterally immarginate. Abdominal segment III more than half size of succeeding segment IV, which is weakly constricted at presegmental portion (uninodal waist). Girdling constriction of segment IV present, i.e. pre- and postsclerites distinct. Cinctus of abdominal segment IV gutter-like, not sculptured. Abdominal segment IV not conspicuously largest segment. Abdominal tergite IV not folding over sternite, and anterior portions of sternite and tergite equally well visible in lateral view. Girdling constriction between pre- and posttergites of abdominal segments V and VI present. Girdling constriction between pre- and poststernites of abdominal segments V and VI present. Pygidium large, with impressed medial field, armed with modified setae, and deeply notched at apex. Hypopygium unarmed. Legs: Mid tibia with single pectinate spur. Hind tibia with single pectinate spur. Hind basitarsus not widening distally, circular in cross-section. Posterior flange of hind coxa not produced as raised lamella. Metatibial gland absent. Metabasitarsal gland absent. Hind pretarsal claws simple. Polymorphism: Monomorphic.

Queen
Borowiec (2016) - Ergatoid, ‘scarcely different in size from the workers’ (Brown 1975) except slightly larger eyes and wider abdominal segment II (petiole). Presence of ocelli unknown.

Male
Borowiec (2016) - Head: Antennae with 12 segments. Clypeus with cuticular apron. Parafrontal ridges absent. Torulo-posttorular complex vertical. Maxillary palps unknown. Labial palps unknown. Mandibles triangular, edentate. Ventrolateral margins of head without lamella or ridge extending towards mandibles and beyond carina surrounding occipital foramen. Carina surrounding occipital foramen ventrally present. Mesosoma: Pronotal flange not separated from collar by distinct ridge. Notauli present. Transverse groove dividing mesopleuron present. Propodeal declivity with distinct dorsal edge or margin. Metapleural gland opening absent. Propodeal lobes present. Metasoma: Petiole anterodorsally immarginate, dorsolaterally immarginate, and laterally above spiracle marginate. Helcium in relation to tergosternal suture placed at posttergite and supraaxial. Prora forming a V-shaped protrusion. Spiracle openings of abdominal segments IV–VI circular. Abdominal segment III more than half size of succeeding segment IV; latter weakly constricted at presegmental portion (uninodal waist). Girdling constriction of segment IV present, i.e. pre- and postsclerites distinct. Cinctus of abdominal segment IV gutter-like, not sculptured. Girdling constriction between pre- and postsclerites of abdominal segments V and VI present. Abdominal segment IV not conspicuously largest segment. Abdominal sternite VII simple. Abdominal sternite IX distally armed with two spines, with lateral apodemes about as long as medial apodeme, directed anteriorly (towards head). Genitalia: Cupula long relative to rest of genital capsule and of approximately equal length on both dorsal and ventral surfaces. Basimere broadly fused to telomere, with sulcus discernable at junction, and ventrally with left and right arms abutting. Telomere gradually tapering toward apex. Volsella narrow, hook-shaped. Penisvalva laterally compressed, rounded at apex. Legs: Mid tibia with single pectinate spur. Hind tibia with single pectinate spur. Posterior flange of hind coxa not produced as raised lamella. Metatibial gland absent. Metabasitarsal glands absent. Hind pretarsal claws simple. Wings: Tegula present, broad, demiovate in shape. Vein C in fore wing present. Pterostigma broad. Abscissa R·f3 absent. Abscissae Rs·f2–3 present, disconnected from Rs+M. Cross-vein 2r-rs present, differentiated from Rs·f4 by presence of Rs·f2–3. Abscissae Rs·f4–5 present, fused in absence of 2rs-m. Abscissa M·f2 in fore wing contiguous with Rs+M. Abscissa M·f4 in fore wing present, reaching wing margin. Cross-vein 1m-cu in fore wing present. Cross-vein cu-a in fore wing present, arising from Cu and distal to, at or near M·f1. Vein Cu in fore wing present, with only Cu1 branch prominent. Vein A in fore wing with abscissae A·f1 and A·f2 present. Vein C in hind wing absent. Vein R in hind wing absent. Vein Sc+R in hind wing present. Abscissa Rs·f1 in hind wing present, shorter than 1rs-m. Abscissa Rs·f2 in hind wing absent. Cross-vein 1rs-m in hind wing fused with M·f1. Vein M+Cu in hind wing present. Abscissa M·f1 in hind wing present. Abscissa M·f2 in hind wing present. Cross-vein cu-a in hind wing present. Vein Cu in hind wing present. Vein A in hind wing with abscissae A·f1 and A·f2 present.

Larvae
Borowiec (2016) - Larva not known. Presence of cocoons unknown.