Taxonomic studies on the ant genus Cerapachys Smith (Hymenoptera, Formicidae) from India

Abstract The Indianspeciesof the ant genus Cerapachys Smith are keyed. Twelve species are recognized of which 6 are described as new. The species are: Cerapachys aitkenii Forel, Cerapachys alii sp. n., Cerapachys anokha sp. n., Cerapachys besucheti Brown, Cerapachys biroi Forel, Cerapachys indicus Brown, Cerapachys longitarsus (Mayr), Cerapachys nayana sp. n., Cerapachys schoedli sp. n., Cerapachys seema sp. n., Cerapachys sulcinodis Emery and Cerapachys wighti sp. n. Geographic distribution and group affinities of the new species are discussed. A revised key to the Indian species is provided. The rare ergatoid queens of Cerapachys nayana, Cerapachys schoedli and Cerapachys seema are reported. Formed in response to selective pressures these ergatoid queens have a significant role in dispersal strategies and contribute much to our understanding of the biology of these ants.


Introduction
The ant genus Cerapachys includes mainly myrmecophagous ants which raid the nests of other ants for prey (Wilson 1959). The genus is distributed widely throughout the tropical and subtropical regions of the world, with the majority of species known from the Indo-Australian region (Brown 1975). Cerapachys is the largest genus in the tribe Cerapachyini and is represented by 153 species globally (Bolton 2013). The tribe was comprehensively covered by Brown (1975), with treatment of 137 described species. Other significant contributions to the genus from South-east Asia include those of Ogata (1983) who described a new species from China; Terayama et al. (1988) provided notes on the Taiwanese species, with the rediscovery of Cerapachys sauteri Forel, 1913 from Taiwan; Morisita et al. (1989) contributed a guide to identification of Japanese species; Radchenko (1993) described the queen of Cerapachys sauteri from Vietnam; Wu and Wang (1995) reviewed the Chinese species; Terayama (1996Terayama ( , 2009 respectively provided keys in addition to descriptions of three new species from Taiwan and Borowiec (2009) discussed the status of the spurious genus Yunodorylus Xu, and described three new species related to Cerapachys sexspinus (Xu, 2000).
Cerapachys in India is currently represented by 6 species (Bharti 2011). The present study reports 6 further new species; C. alii sp. n., C. anokha sp. n., C. nayana sp. n., C. schoedli sp. n., C. seema sp. n., and C. wighti sp. n. from the southwest of the country. Cerapachys is thus now represented by 12 Indian species, a revised key to which is provided here. The present study aims to describe and catalogue the diversity of Cerapachys species from India and to discuss group affinities based upon available data.

Materials and methods
The specimens were collected by hand and Winkler extraction. Taxonomic analysis was conducted using a Nikon SMZ 1500 stereo zoom microscope. For digital images, an MP evolution digital camera was used on the same microscope with Auto-Montage (Syncroscopy, Division of Synoptics, Ltd.) software. Later, images were cleaned as per requirement with Adobe Photoshop CS6. Description style and morphological terminology for measurements and indices follow Brown (1975) and Borowiec (2009)      Punctures on dorsum of head relatively small, their diameter smaller than the average distance separating them (Fig. 6A)

Descriptions of new species
Mesosoma. Stout, wider anteriorly; dorsal surface slightly convex, almost flat, the dorsal surface gently rounded along sides without any distinct margin. Declivous face of propodeum with cariniform margins across the top and along lateral margins.
Metasoma. Petiole as long as broad, without overhanging dorsolateral margins. Anterior face transverse and posterior face shallowly convex. Subpetiolar process prominent, acute, posteriorly directed; no fenestra present. Postpetiole slightly longer than broad, lateral angles uniformly rounded. Gaster elongate; base of cinctus of first gastral tergite with cross ribs; sting exerted.
Vestiture. Body with reduced white pilosity; moderate, decumbent or subdecumbent hairs distributed evenly throughout. Apical funicular segments and legs with small standing hairs.
Colour. Dark red with mandibles, antennae and legs castaneous. Etymology. The species is named in honor of Dr. Salim Ali, renowned Indian Ornithologist.
Differential diagnosis. With its 9 segmented antennae C. alii can be easily separated from other species known from India. Only eight other known species of Cerapachys are reported to have 9 segmented antennae. These eight species are placed in the typhlus group and include; C. biroi Forel, 1907;C. cryptus Mann, 1921;C. edentatus Forel, 1900;C. fuscior Mann, 1921;C. papuanus Emery, 1897;C. pawa Mann, 1919;C. pusillus Emery, 1897 andC. typhlus Roger, 1861. The new species can be easily separated from all of them. C. cryptus and C. fuscior are larger species (HW> 0.70 mm) while C. alii is a smaller species (HW< 0.40 mm). C. typhlus has the postpetiole more than half as long as the succeeding gastric segment while in C. alii it is less than half as long as the succeeding gastric segment. C. papuanus, C. pawa and C. pusillus have the anterolateral shoulders of the first gastric segment abruptly rounded, accentuating the medium concavity that receives the postpetiole while in C. alii the anterolateral shoulders of the first gastric segments as seen from above broadly rounded and gradually widening caudad. C. biroi and C. edentatus predominantly have punctuate body sculpture while C. alii has predominantly foveate body sculpture. C. alii can also be confused with C. fragosus Roger, 1862 and C. coecus Mayr, 1897 which has similar prominent foveate body sculpture, however these two species are characterized by 11 segmented antennae while as C. alii has 9 segmented antennae.
Ecology. This subterranean species seems to be of rare occurrence as it was encountered only once during the extensive surveys in the region. The specimens were collected from a leaf litter sample taken from Salim Ali bird Sanctuary. A low-land evergreen forest area, located between the branches of Periyar river. The region is considered as the richest bird habitat on peninsular India.  Head. Rectangular, longer than broad, widest at about mid-length; sides parallel; vertexal margin slightly concave, posterior lateral corners are weakly acute to rounded.

Cerapachys anokha
Parafrontal ridges present. Eyes prominent, placed below midline of head. Mandible triangular with acute apices and sharp concave, edentate, masticatory margins; anterior clypeal margin with small apron shaped transparent structure. Lateroclypeal teeth small, blunt and projecting slightly inwards. Antennae 12 segmented; scape short and clavate, reaching up to 1/3 rd of posterior margin of head.
Mesosoma. Stout, rectangular in dorsal view; dorsal surface convex, the dorsal surface gently rounded along sides without any distinct margin. Declivous face of propodeum lacking cariniform margins across the top and along sides.
Metasoma. Petiole highly convex, broader than long, with traces of reduced dorsolateral margins, anterior and posterior faces continuous with dorsum. Subpetiolar process prominent, wedge like, with apex directed backward; no fenestra present. Postpetiole wider than long, uniformly rounded. Gaster elongate; base of cinctus of first gastral tergite with cross ribs; sting exerted.
Sculpture. Mandibles smooth and shining. Head with few small punctures. Sculpture on dorsal surface of mesosoma, petiole and postpetiole consist of very small, uniform punctures, distributed throughout the surface. Gaster mostly smooth, with few scattered punctures. Cinctus of 1 st gastral, with few cross ribs.
Vestiture. Body covered with decumbent or subdecumbent hairs. Longer hairs are also present on postpetiole and gaster. Head also consists of few long hairs; apical funicular segments and legs with standing hairs.
Colour. Black with mandibles, antennae and legs castaneous. Etymology. The species epithet is Hindi for "unique", in reference to its unique nature of propodeal declivity. Differential diagnosis. This species is unique in having the declivous face of the propodeum lacking cariniform margins across the top and along the sides, features unique in described workers of the Cerapachyinae. The new species show interesting variation in the form of the petiole. The petiolar node has the inferior as well as the superior posterolateral angles produced, but not sharply angular. The sides of the petiole could not be considered either immarginate (Cerapachys lineage) or marginate (Phyracaces lineage). This makes the placement of this species somewhat transitional between the two lineages and easily distinguishes it from other reported species of the genus. When using Brown`s (1975) key C. anokha comes close to singaporensis Viehmeyer, 1916. The two species however can be easily separated. C. singaporensis has the body arrayed with long pale hairs; and copiously pubescent, and the dorsal sides of the petiole strongly marginate, while C. anokha has only decumbent or subdecumbent body hairs, little pubescence and the dorsolateral sides of petiole are not marginate. C. anokha could also be confused with C. nayana which has similar habitat preferences and body colouration; however the two species can be easily separated: C. nayana has larger eyes (EL 0.24-0.27 mm), the declivous face of the propodeum has cariniform margins across the top, and the petiole has marginate dorsolateral sides; while C. anokha has smaller eyes (EL 0.20-0.22 mm), the declivous face of its propodeum lacks cariniform margins across the top, and the petiole is without marginate dorsolateral sides.
Ecology. This species seems to be infrequent. It is from the Western Ghats. Four specimens were collected by handpicking from the Thanikkudy region of the Periyar tiger reserve. Which is a primary, undisturbed tropical moist evergreen forest. The area is situated at 1003 meters elevation. It is a shady place with little sunlight penetration.
Mesosoma. Moderately stout, rectangular in dorsal view; dorsal surface flattened, bordered laterally by a distinct angle, but no margin. Declivous face of propodeum with cariniform margins across the top and along the lateral margins.
Metasoma. Petiole broader than long, with strong overhanging dorsolateral margins. Anterior face concave while posterior face is transverse. Subpetiolar process small with stout acute apex, directed forward, located beneath anterior 1/3rd of the petiole; no fenestra present. Postpetiole sub trapezoidal, wider behind with the posterolateral angles uniformly rounded. Gaster elongate; base of cinctus of first gastral tergite with cross ribs; sting exerted.
Sculpture. Mandibles smooth and shining. Head with small punctures, spaced wider than their diameter, dorsum of head also with faint rugae in between the punctures. Similar sculpture on dorsal surface of mesosoma and petiole. Small continuous punctures produce a matt like appearance on the dorsum of the postpetiole. Gaster with similar mattlike appearance but less prominent. Cinctus of 1 st gastral segment smooth and shining.
Vestiture. Body covered with moderate decumbent or subdecumbent hairs most prominent on postpetiole and gaster, head devoid of such hairs, only a few along sides; apical funicular segments with standing hairs.
Colour. Black with mandibles, antennae and legs castaneous. Like the workers of the same colony, but larger, with thicker body, especially mesosoma and gaster. Ocelli present on vertex, prominent. The pilosity is much more prominent compared to workers. Distinction between ergatoid queens and worker is vague, with size variation of workers very high.
Variations. There is a considerable amount of size variation between individual specimens, the smaller workers are lighter in body colouration compared with larger specimens; the body sculpture and pilosity also differs between individuals.
Etymology. The species epithet is Sanskrit for "eyes", in reference to the large eye size of the species. Differential diagnosis. With the marginate dorsolateral sides of its petiole, this species is easily distinguished from other Indian species of its genus. The new species shares most characters with C. anokha from which it is separated by the combination of characters given in the diagnosis of the latter species. C. nayana is compared with C. longitarsus which also has marginate dorsolateral sides to the petiole; however, the two species can be easily separated. C. longitarsus has characteristic bicolouration, with the head brown, trunk red or brown, petiole and postpetiole light to dark reddish and the gaster brown or black, while C. nayana is uniformly black coloured with mandibles, antennae and legs castaneous. The new species also resembles the Philippines, C. luzuriagae (Wheeler & Chapman, 1925) but can be easily separated from it. C. nayana is coloured black with the petiole broader than long, and with concave anterior and transverse posterior faces, the postpetiole with dense punctures and without dentition; while C. luzuriagae is reddish brown with the petiole as long as broad, with convex anterior and truncate posterior faces; postpetiole without dense punctures, and mandibles with prominent dentition.
Ecology. This species is widely distributed in the Western Ghats. It was collected from non-forested and forest habitats from small bushes, and foraging over dry soil surfaces.  Head, rectangular, longer than broad; sides parallel; vertexal border transverse. Posterior lateral corners acute. Parafrontal ridges present, raised. Eyes medium sized, almost circular. Mandibles subtriangular; masticatory margins without a row of small denticles. Lateroclypeal teeth small. Antennae 12 segmented; scapes short, each falling short of posterior margin of head by 1/3 rd of its length.

Cerapachys schoedli
Mesosoma. stout, humped in profile view; dorsal surface convex, continuous with sides, no lateral margins. Declivous face of propodeum with cariniform margins across the top and along the lateral margins.
Metasoma. Petiole broader than long, and gently rounded towards the sides. Anterior and posterior faces transverse. Subpetiolar process stout, fenestra present. Postpetiole almost rectangular, wider behind, with the posterolateral angles not tuberculate but uniformly rounded. Gaster elongate; base of cinctus of first gastral tergite with cross ribs; sting exerted.
Sculpture. Mandibles with small punctures. Head smooth and shining with some punctures. Mesosoma mostly smooth and shining with some punctures along the sides. Petiole, postpetiole and gaster with continuous punctures.
Vestiture. Body covered with moderate, decumbent or subdecumbent hairs, most prominent on gaster; apical funicular segments and legs also with standing hairs.
Like the workers of the same colony, but larger, with more stout body, especially the mesosoma and gaster. Ocelli absent on vertex. Distinction between ergatoid queens and worker is vague, with size variation of workers very high.
Etymology. The species is named in the honor of the late Dr. Stefan Schödl. Differential diagnosis. This species is aberrant in many characters, with the cephalic dorsum bearing small punctures with average diameter lesser than the average distance separating them, a highly shinning body and reduced body sculpture, which separates it from other reported Indian species. C. schoedli shares most characters with C. seema, from which it can be easily distinguished by the combination of characters given in the diagnosis of the latter species. The new species can also be compared with C. luteoviger Brown, 1975 which also has small punctures on the cephalic dorsum, with diameter lesser than the average distance separating them. However, the peculiar petiolar node (with anterodorsal border concavely emarginate) and rounded head shape of C. luteoviger easily separates it from C. schoedli, which has the petiolar node broader than long and the posterior lateral corners of the head acute.
Ecology. This species seems to be common in the Western Ghats; it was collected in non-forest as well as forest habitats in leaf litter and on dry soil surfaces.
Metasoma, Petiole broader than long, lacking dorsolateral margins. Anterior and posterior faces transverse. Subpetiolar process well developed, located below the anterior 1/3 rd of the petiole; fenestra present. Postpetiole broader than long with posterolateral angles uniformly rounded. Gaster elongate; base of cinctus of first gastral tergite with cross ribs; sting exerted.
Sculpture. Mandibles smooth with few punctures. Head with prominent punctures, spaced more widely than their diameter. Similar sculpture on dorsal surface of mesosoma. Petiole and postpetiole with larger punctures, forming a rugae-like surface on the dorsum. Gaster with similar sculpture to mesosoma. Cinctus of 1 st gastral segment with prominent transverse ribs.
Vestiture. Whole body covered with dense decumbent or subdecumbent yellowish hairs, sides of head and mesosoma with fewer hairs; apical funicular segments and legs with standing hairs.
Colour. Dark brownish black with mandibles, antennae and legs castaneous. Like the workers of the same colony, but larger, with a more stout body, especially the mesosoma and gaster. Ocelli present on vertex, prominent. The pilosity is much more prominent when compared with the workers. Distinction between ergatoid queens and workers is vague with size variation of workers very high.  Resembles the worker, with modifications expected for caste and the following differences; three prominent ocelli present on vertex, thicker body with heavy pilosity and prominent sculpture.
Etymology. The species epithet is Hindi for border, in reference to its type locality, Manalar, a place which marks border between Kerala and Tamil Nadu.
Differential diagnosis. The species is characterized by the punctures on the dorsum of the head being relatively small, separated, with their diameter smaller than the average distance separating them. The new species shares most characters with C. schoedli. However the two species can be easily separated. C. seema has dull body colouration, sculpture much more prominent and course, pilosity denser, eyes not breaking the lateral margins of head and head almost oval, with anterior and posterior sections of the sides converging, while C. schoedli is brightly coloured, its sculpture and pilosity are reduced, its eyes break the lateral margins of the head and the head is rectangular with parallel sides.
Ecology. Manalar, part of Periyar tiger reserve, the type locality of this species is a fascinating green hill station (with plenty of leaf litter) surrounded on all sides by the tea gardens of Tamil Nadu. This species was found nesting beneath the marker stone on the border which separates Kerala and Tamil Nadu. It is presumed that the nest was in its initial stages of establishment as there were hardly any galleries and underground chambers. A single queen, 3 ergatoid queens and 7 workers were collected. This species seems uncommon in the Western Ghats range, since it was not encountered again from any other locality.  Head rectangular, longer than broad; sides rounding posteriorly, vertexal margin transverse, posterior lateral corners gently rounded, weakly acute. Parafrontal ridges raised, prominent. Eyes reduced. Mandibles subtriangular; masticatory margin without a row of small denticles. Lateroclypeal teeth reduced. Antennae 12 segmented; scapes short, clavate.

Cerapachys wighti
Mesosoma stout, compact, rectangular in dorsal view; dorsal surface slightly convex, the sides gently rounded without any distinct margin. Declivous face of propodeum with the upper sides margined.
Petiole broader than long, without strong overhanging dorsolateral margins. Anterior and posterior faces transverse. Subpetiolar process stout with hook like ventral margin; no fenestra present. Postpetiole sub trapezoidal, wider behind, posterolateral angles uniformly rounded. Gaster elongate; base of cinctus of first gastral tergite with cross ribs; sting exerted.
Sculpture. Mandibles punctured. Punctures on dorsum of head large, crowded, their diameter as large, or larger than, the average distance separating them. Mesosoma, petiole and postpetiole similarly sculptured. Gaster with smaller sized punctures compared with head, mesosoma and metasoma. Cinctus of 1 st gastral with cross ribs.
Vestiture. Body with reduced pilosity; moderate decumbent or subdecumbent hairs. Mostly prominent on postpetiole and gaster. Apical funicular segments and legs with standing hairs.
Colour. Dark reddish brown with mandibles, antennae and legs lighter Etymology. The species is named after botanist Robert Wight, who historically explored the area in 1847.
Differential diagnosis. The new species can easily be separated from most of the Indian species on the basis of the large crowded punctures on its cephalic dorsum, with diameter as large, or larger than, the average distance separating them. C. wighti shares most characters with C. indicus, which also has large crowded punctures on cephalic dorsum. However the two species can be easily separated. C. wighti is smaller in size (HW 0.59 mm), has lighter body colouration and reduced eyes (EL 0.05 mm), while C. indicus is larger in size (HW 0.77 mm), with darker body colouration and large eyes (EL 0.24 mm). Ecology. The species seems to be of rare occurrence as it was encountered only once during the extensive surveys conducted in the area. It was collected from a litter sample taken near the Kuntipuzha river, which drains the entire length of the silent valley national park. With a pesticide free catchment area the region is rich in soil biota and ideal for cryptic ant species.
General discussion. Here we present a review of genus Cerapachys from India. 12 species are recognized of which 6 are described as new. Partly for convenience the 12 Indian species are placed into arbitrary groups. Group I species with 12 segmented antennae viz., C. sulcinodis, C. anokha, C. schoedli, C. seema, C. indicus, C. aitkenii, C. wighti, C. longitarsus and C. nayana. Of the 9 species given above the first four i.e., C. sulcinodis, C. anokha, C. schoedli and C. seema, have the punctures on the dorsum of the head relatively small, separated, with their diameter smaller than the average distance separating them. Among these C. anokha, with the declivous face of the propodeum lacking cariniform margins, and C. sulcinodis, with the dorsal surface of the petiolar node with a smooth, median area are distinct species in the group. C. schoedli and C. seema are easily separated. C. seema has dull body colouration, sculpture much more prominent and coarse, pilosity denser and head almost oval, with the anterior and posterior sections of its sides converging, while C. schoedli is brightly coloured, with sculpture and pilosity reduced and the head rectangular with parallel sides. The next 3 species i.e., C. indicus, C. aitkenii and C. wighti, have the punctures on the dorsum of the head large, their diameter greater than the average distance separating them. Among these C. wighti has the smallest size (HW 0.59 mm) and relatively reduced eyes (EL 0.05 mm) wereas C. aitkenii and C. indicus are easily separated from each other on the basis of body sculpture and colouration. C. aitkenii has characteristic bicolouration and its body sculpture is foveate, wereas C. indicus is mostly piceous with bluish iridescent sheen and reduced sculpture. The remaining 2 species i.e., C. longitarsus and C. nayana are members of 'Phyracaces lineage' and easily recognized, with strong overhanging dorsolateral margins to the petiole. The two species are separated from each other on the basis of body colouration. C. longitarsus has characteristic bicolouration with head brown, trunk red or brown, petiole and postpetiole light to dark reddish and gaster brown or black, while C. nayana is uniformly black in colour, with mandibles, antennae and legs castaneous. Group II species have antennae with less than 12 segments viz., C. biroi, C. alii and C. besucheti. Among these C. besucheti has 11 segmented antennae while C. biroi and C. alii have 9 segmented antennae. C. biroi is characterized by its opaque body with closely spaced piligerous punctures, while C. alii has prominent foveate body sculpture.
Workers grade into a number of "atypical" reproductives. These morphologically "atypical" ant reproductives have been assigned a number of descriptive terms. However Peeters (2012) advocate use of "ergatoid queens" for all wingless reproductives that differ morphologically from workers. These ergatoid queens are formed as a response to selective pressures against long range dispersal and solitary colony foundation (Peeters and Molet 2010). Ergatoid queens have been reported previously in Cerapachys (Brown, 1975). Here we present ergatoid queens of three more species -C. nayana, C. schoedli and C. seema. In evaluating morphometric data of the three castes of C. seema i.e. worker, ergatoid queens and queen castes (Fig. 41) it is observed that ergatoid queens are Figure 41. Graph plotted on evaluating morphometric data shows less affinity of ergatoid queens with workers compared with gyne/queen.

N Species
Distribution EQ Q M W 1 C. alii sp. n.
India, Kerala ---+ 3 C. aitkenii Forel, 1900 India, Kerala --+ 4 C. besucheti Brown, 1975 India, Tamil Nadu + --+ 5 C. biroi Forel, 1907 Madagascar  ---+ closer to gynes than the workers. Further inference and analysis on the subject is beyond the scope of this paper and would require much more information. However the aim of this review is to add further material for examination for understanding this fascinating aspect of ant biology and to promote more studies in this direction. Notes. Cerapachys keralensis Karmaly, 2012 described on the basis of two minor? workers collected from the Palakkad district of Kerala. The new species is highly dubious. The description is minimal, superficial and contains no comparative notes. The photographs are derisory as illustrations supporting the inadequate descriptions. Cerapachys keralensis Karmaly, 2012 is here considered to be a species inquirenda.
Two unpublished new species (C. browni and C. costatus; Bharti and Wachkoo (in press)) are excluded from this paper. The two species can be easily separates from other reported Indian species. C. browni shares most affinities with C. aitkenii but with black colour (unicolorous), rugo-reticulate sculpture and strongly constricted cintus of gaster. C. costatus with remarkable costate sculpture, which is not reported in any other Indian species.