Zasphinctus

Zasphinctus is a moderately speciose lineage of specialized ant predators, most prominent in Australia. These ants are rarely collected and the material housed in natural history collections is somewhat limited.

Identification
Borowiec (2016) - Worker The workers of Zasphinctus are ants of variable size, color, and sculpturation, but always possessing conspicuous girdling constrictions between abdominal segments IV, V, and VI. The eyes absent in most species. Zasphinctus can be distinguished from other lineages with pronounced abdominal constrictions by highly-positioned propodeal spiracles, propodeal lobes present, pygidium large and armed with modified setae, and pronotomesopleural suture fused. See also diagnoses of Eusphinctus and Sphinctomyrmex.

Male The males of Zasphinctus also possess the characteristic abdominal constrictions between abdominal segments IV, V, and VI and can be recognized by a combination of costal vein (C) absent from the fore wing, submarginal cell (SMC) closed by Rs·f2-f3, vein 2rs-m absent, pronotum not marginate anterodorsally, and antennae 13-segmented. This venation is similar to Lividopone and Parasyscia but Zasphinctus can be recognized by the presence of abdominal constrictions and different appearance of abdominal sternite IX (subgenital plate). In Zasphinctus, the sternite is abruptly constricted proximal to where spines arise and is much wider at midlength. In Lividopone and Parasyscia in contrast, the sternite IX is usually gradually narrowing to the point of bifurcation. The males of Eusphinctus and Sphinctomyrmex have similar abdominal constrictions but the former has 12-segmented antennae and the latter has different wing venation with costal vein present.

Brown (1975) gave a preliminary key to Indomalayan and Australasian species.

Hita Garcia et al. (2017) Afrotropical Zasphinctus (workers) The following diagnosis is based on Borowiec (2016) with modifications and additions to encompass just the Afrotropical species:

HEAD: Antennae with 12 segments and relatively short (SI 47–57), far from approaching posterior head margin. Apical antennal segment conspicuously enlarged, longer than two preceding segments combined. Head distinctly longer than broad (CI 78–86). Clypeus with cuticular apron. Lateroclypeal teeth absent. Parafrontal ridges present and well developed. Torulo-posttorular complex vertical. Antennal scrobes absent. Labrum with median notch or concavity. Proximal face of stipes not projecting beyond inner margin of sclerite, prementum exposed when mouthparts fully closed, even though only slightly so. Maxillary and labial palps 3-segmented (see section on mouthparts below). Mandibles elongate triangular, masticatory margin with 4 or 5 small denticles on basal half, denticles usually strongly reduced and inconspicuous. Eyes and ocelli absent. Head capsule with weakly to well 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: Mesosoma in profile relatively low and elongate to moderately high and stocky (LMI 34–41). In dorsal view usually slightly more than twice as long as broad (DMI2 49–58). Pronotal flange separated from collar by distinct ridge. Promesonotal connection with suture completely fused. Pronotomesopleural suture absent. Mesometapleural groove not impressed or weakly impressed. Transverse groove dividing mesopleuron absent. Pleural endophragmal pit concavity present, weakly to well developed. 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 and well developed.

LEGS: Mesotibia with single pectinate spur. Metatibia with single pectinate spur. Metabasitarsus not widening distally, circular in cross-section. Posterior flange of hind coxa not produced as raised lamella. Metatibial gland an oval patch of whitish cuticle. Metabasitarsal gland absent. Pretarsal claws of metatibia simple. Metafemur short to moderately long (MFI 75–100).

METASOMA: Abdominal segment II (petiole) sessile without peduncle and petiolar node well developed. In profile petiolar tergum between 1.0 to 1.2 times longer than high (LPI 102–123). Petiole anterodorsally marginate, dorsolaterally rounded, and laterally above spiracle weakly marginate. Laterotergites well developed and clearly demarcated. Sternum of petiole well developed with strongly anteroventrally projecting subpetiolar process, process with or without fenestra. Helcium axial and in relation to tergosternal suture placed at posttergite. Prora simple, not delimited by carina. Prora forming a U-shaped margin with median ridge. Spiracle openings of abdominal segments IV–VI circular. Abdominal segment III anterodorsally immarginate and dorsolaterally immarginate. In profile view abdominal segment III distinctly larger than succeeding segment IV, in dorsal view abdominal segment III longer than segment IV. Cinctus of abdominal segment IV not impressed. Girdling constrictions of segments IV, V, VI present and distinct, either unsculptured or cross-ribbed. Abdominal tergite IV not folding over sternite, and anterior portions of sternite and tergite equally well visible in lateral view. Pygidium large, with weakly impressed medial field.

SETATION: Most of body with numerous short to moderately long, appressed to suberect (very rarely erect) setae. Pygidium armed with modified, thick, and often peg-like setae. Hypopygium armed with modified setae.

COLOURATION: All known species predominantly dark brown to black with often lighter appendages.

Distribution
Borowiec (2016) - Distributed throughout Australasia, including New Caledonia and New Guinea, and the Afrotropics. Most species are known from Australia, with only three taxa described from Africa. Recently a species has been described from Thailand (Jaitrong et al. 2016), and unidentified Zasphinctus males are also known from Myanmar (author’s unpublished observations).

Biology
Hita Garcia et al. (2017) - Perhaps due to its moderate species richness and relative rarity of collections, knowledge about the biology of Zasphinctus is rather incomplete. Wilson (1958) and Brown (1975) provided field notes about the biology of Zasphinctus steinheili and laboratory observations of Zasphinctus caledonicus. Both species turned out to be myrmecophagous feeding on larvae and adults of a variety of ant species captured during nest raids. Later, Buschinger (1989) confirmed this behaviour in Z. steinheili under laboratory conditions. Based on data from Z. steinheili and Z. caledonicus, colonies are found in soil and range in size from 100 to 500 workers. However, whether or not this is true for other Zasphinctus species, especially outside Australia, remains unknown.

There is no information known about the natural history of Afrotropical Zasphinctus, except that they might live in leaf litter since most specimens were collected in litter samples. Against the background that they are dorylines and that their Australian congeners are predators of other ants, it is likely that the species treated in this study pursue a similar lifestyle.

Briese (1984) described a nest evacuation response in a Monomorium species raided by Zasphinctus in Australia. Hölldobler et al. (1996) described the metatibial gland of Z. steinheili.

Morphology
Hita Garcia et al. (2017) - All three Afrotropical Zasphinctus  species possess a very thick cuticle. Peeters et al. (2017) found the species with the thickest cuticle in relation to body size to be predominantly large ponerine genera, such as Diacamma, Odontoponera, Leptogenys, and Ectomomyrmex. However, the thickest cuticle was observed in the species Ooceraea biroi (Forel), which is a doryline in relative close phylogenetic proximity to Zasphinctus. Based on that result, it is not that surprising that African Zasphinctus display such thick cuticle. Notwithstanding that Peeters et al. (2017) found that the best predictors for thick cuticle were body size (larger ants have thicker cuticle) and phylogeny (poneroid ants have thicker cuticle), the thick cuticle of African Zasphinctus is likely related to a predatory lifestyle. Based on observations of other Zasphinctus species mentioned above, it is highly probable that African Zasphinctus are top predators that feed predominantly on other ants, which is also the case in the clonal raider ant Ooceraea biroi, which feeds primarily on ant brood. Furthermore, Peeters et al. (2017) concluded that cuticle thickness was also negatively correlated with larger colony size in more phylogenetically derived ant lineages (formicoid clade). Despite a severe lack of observation and natural history data, it appears that African Zasphinctus live in small colonies, which is well in accordance with the findings of Peeters et al. (2017).

In Zasphinctus, the relative amount of muscles responsible for moving the abdomen seems to be largely increased compared to other ants from the formicoid clade, e.g. Pheidole and Terataner, studied in previous publications (Sarnat et al. 2016; Hita Garcia et al. 2017a). It may be tempting to think that the genus Zasphinctus – as compared to the majority of ant lineages which have (evolved) greatly reduced abdominal musculature – has retained a more ‘primitive’ and wasp-like internal morphology in its abdomen. Yet, its species have a morphology that makes them rather special among ants: their relatively long abdomen is serially constricted between individually rotating presclerital plates. This apparent adaptation may have gained Zasphinctus additional functionality during predation and defence by increasing overall flexibility of use for its well-developed sting apparatus in the apical abdominal segment. It seems that other doryline genera such as for example Eusphinctus, Sphinctomyrmex Mayr, and to a lesser degree possibly some Cylindromyrmex, and Leptanilloides have evolved very similar features independently from Zasphinctus.

Nomenclature

 *  ZASPHINCTUS  [Dorylinae]
 * Zasphinctus Wheeler, W.M. 1918a: 219 [as subgenus of Eusphinctus]. Type-species: Sphinctomyrmex turneri, by monotypy.
 * Zasphinctus junior synonym of Sphinctomyrmex: Brown, 1975: 31.
 * Zasphinctus as genus: Borowiec, 2016: 237.

Taxonomic Notes
Borowiec (2016) - This name is here revived from synonymy with Sphinctomyrmex. For a brief account of taxonomic history and justification see under Eusphinctus. The position of Zasphinctus within dorylines appears to be well established as the sister group to Parasyscia, and it is reasonably certain that this lineage was derived independently from the Neotropical Sphinctomyrmex (Figure 1; Brady et al. 2014, Borowiec, in prep.).

Hita Garcia et al. (2017) - Prior to this study the taxonomy of Zasphinctus in the Afrotropical region was solely based on two male-based species described more than a hundred years ago from West African savannahs (Santschi 1915). Since then, no further taxonomic studies on Zasphinctus were published and the scarce male-based or worker-based material in collections has been tentatively assigned to one of these male-based species without evidence of any association. Recent collections in Kenya (Hita Garcia et al. 2009), Mozambique, and Uganda have yielded worker-based material without any males, thus not associable to any valid species name.

At the beginning of our study we encountered a situation in which the only two valid species from the region were described from males from West Africa (Santschi 1915), whereas the material available to us consisted of three worker-based species not associated to any males. A DNA-based association is currently not possible since the two male-based species are only known from their respective type material, thus not available for any molecular analysis. There are additional males available from Nigeria and Uganda, but they are also not associated with any workers and their conspecificity with the other male-based species is uncertain. Since Zasphinctus is one of the rarest ant genera in the region, it is not likely that more specimens than currently available will be collected anytime soon, which means that the lack of male-worker association problems will remain. Furthermore, the two male-based species were collected in relatively arid savannah areas in West Africa while two of the worker-based species are from humid equatorial rainforests. The third worker-based species is from a savannah in Mozambique, thus geographically distant from the two male-based species.

These discrepancies led us to describe the three worker-based species independently from the already known male-based species and create a comprehensive worker-based taxonomic system for the genus in the Afrotropical region. With this approach, we follow Wilson (1964) who suggested temporarily ignoring the male-based names and establishing a sound worker-based taxonomy until males are found together with workers and the different taxonomic names can be harmonised. More recent authors concur with that approach and also opine that male-based names will eventually be matched with worker-based names using molecular data (Jaitrong and Yamane 2011; Liu et al. 2015; Staab 2015).

Worker
Borowiec (2016) - Head: Antennae with 11 or 12 segments. Apical antennal segment conspicuously enlarged, much broader than and longer than two preceding segments combined. Clypeus with cuticular apron. Lateroclypeal teeth absent or present. Parafrontal ridges absent or reduced. Torulo-posttorular complex vertical. Antennal scrobes absent. Labrum with median notch or concavity. Proximal face of stipes not projecting beyond inner margin of sclerite, prementum exposed when mouthparts fully closed. Maxillary palps 3-segmented. Labial palps 3-segmented. Mandibles triangular, with teeth or edentate. Eyes absent or present, composed of more than 20 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 or not. Promesonotal connection with suture completely fused. Pronotomesopleural suture completely fused. Mesometapleural groove not impressed or weakly impressed. Transverse groove dividing mesopleuron absent or 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 marginate or immarginate, dorsolaterally immarginate, and laterally above spiracle marginate or rarely immarginate. Helcium in relation to tergosternal suture placed at posttergite and helcium axial, occasionally slightly supraaxial. Prora simple, not delimited by carina. Prora forming a U-shaped margin with median ridge. 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 not impressed. 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, and armed with modified setae, sometimes notched. Hypopygium armed with modified setae. 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 or an oval patch of whitish cuticle. Metabasitarsal gland absent. Hind pretarsal claws simple. Polymorphism: Monomorphic.

Queen
Borowiec (2016) - Alate, ergatoid, or subdichthadiigyne. Alate gynes are known in an undescribed species from Africa (Brown 1975) and in Zasphinctus occidentalis (Clark 1924a). In Zasphinctus asper, Zasphinctus duchaussoyi, and Zasphinctus steinheili known gyne specimens are wingless ergatoids that possess eyes and ocelli. The gyne of Zasphinctus imbecilis can be considered a ‘subdichthadiigyne’; it possesses only vestigial eyes and one or no ocelli in addition to enlarged gaster. Descriptions and extensive discussions of gyne morphology in Zasphinctus can be found in Brown (1975), Clark (1924a), and Wheeler (1918).

Male
Borowiec (2016) - Head: Antennae with 12 or 13 segments. Clypeus with cuticular apron. Parafrontal ridges absent. Torulo-posttorular complex vertical. Maxillary palps 3-segmented. Labial palps 3-segmented. Mandibles triangular, edentate to falcate. 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 separated from collar by distinct ridge. Notauli present or, more rarely, absent. Transverse groove dividing mesopleuron present. Propodeal declivity with distinct dorsal edge or margin. Metapleural gland opening absent. Propodeal lobes present. Metasoma: Petiole anterodorsally marginate, dorsolaterally immarginate, and laterally above spiracle marginate. Helcium in relation to tergosternal suture placed at suture and axial. 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 curved dorsally at apices, with lateral apodemes shorter than or about as long as medial apodeme, directed anteriorly (towards head); all apodemes long. Genitalia: Cupula long relative to rest of genital capsule and shorter ventrally than dorsally. Basimere broadly fused to telomere, with sulcus discernable at junction, and ventrally with left and right arms abutting. Telomere gradually tapering toward apex. Volsella laterally flattened, at apex with dorsal lobe and hooked ventrally. 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 present as oval patch of whitish cuticle. Metabasitarsal glands absent. Hind pretarsal claws simple. Wings: Tegula present, broad, demiovate in shape. Vein C in fore wing absent. Pterostigma broad. Abscissa R·f3 absent. Abscissae Rs·f2–3 present, connecting with Rs+M&M·f2 or 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 present, separated from Rs+M by Rs·f2. Abscissa M·f4 in fore wing present, not reaching wing margin. Cross-vein 1m-cu in fore wing present. Cross-vein cu-a in fore wing present, arising from M+Cu and proximal to M·f1 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 absent. Abscissa Rs·f1 in hind wing not differentiated in absence of Sc+R. Abscissa Rs·f2 in hind wing present, not reaching wing margin. 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 absent. 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; The latter a stub.

Larva
Cocoons present.