Revision of the oriental ant genus Cladomyrma, with an outline of the higher classification of the Formicinae (Hymenoptera: Formicidae)

Abstract. The Oriental ant genus Cladomyrma is revised and possible phylogenetic relationships are discussed. Cladomyrma hewitti and hobbyi are newly synonymized with andrei. Cladomyrma cryptata, maschwitzi, mossyna and petalae are described as new species. A lectotype for Cladomyrma hewitti is designated. A synopsis of the classification of Formicinae, based on new morphological characters, is provided. New morphological characters at the generic level are described and the relationships of Cladomyrma within Formicinae are discussed.


Introduction
This study was initiated by a discussion of the phylogenetic relationships of the old world genera Aphomomyrrnex, Cladomyrma and Petalomyrmex and the new world genus Myrmelachista; all, except some in Myrmelachista, obligatory inhabitants of internodes of rainforest trees, especially legumes (McKey, 1991). Their life style, living in branches and hollow internodes of climbers and trees, which are actively opened by the queen, is a possible synapomorphy for these genera (U. Maschwitz and D. McKey, pers. comm.), All the queens of these ant genera show a similar flattened head and alitrunk, which has been interpreted as an adaptation to their life in plant cavities (Wheeler, 1910;Snelling, 1979;McKey, 1991), and therefore the question has been raised as to whether they form a monophyletic taxon D. McKey, pers. comm.).
The old world genera of this assemblage of arboreal ant genera (i.e. Aphomomyrmex, Cladomyrma and Petalomyrmex) are all rarely collected and thus are poorly represented in our Correspondence: Dr Donat Agosti, Tagerackerstr. 16, CH-861O Uster , Switzerland. collections. Furthermore, the descriptions of the three Cladomyrma species are based on queens, which are mainly caught by light traps. This makes the association of recently collected workers with the described queens difficult. Samples collected during recent biological studies of Cladomyrma in Malaysia , could not be identified to species level, and it became apparent that there were several undescribed species. This paper has three purposes: to discuss the phylogenetic placement of Cladomyrma within the Formicinae; to assess possible relationships of Cladomyrma with Aphomomyrmex, Myrmelachista and Petalomyrmex; and to provide a revision of Cladomyrma species needed by workers currently studying their biology.
The Formicinae includes forty-eight recent genera, with approximately 3000 described species mostly in tropical regions. Members of this subfamily are diagnosed by the acidopore at the apex of the terminal gastral sternite, by the reduction of the sting apparatus to two lateral spiracular plates, a median connection and an anal are, and a replacement of the sting with an acid-spraying system, and by a highly modified proventriculus (Emery, 1925;Eisner, 1957). Beside the proventricular structure, no external morphological characters are known to diagnose the males of Formicinae. Nevertheless, the Formicinae are considered a monophyletic taxon, with the above-mentioned characters as autapomorphies. Keys to the subfamilies and the genera, a synopsis of the genera and an overview of formicine behaviour and ecology is provided by Holldobler & Wilson (1990); the distribution of the genera is summarized by Brown (1973).
Cladomyrma was described by Wheeler (1920) as a myrmelachistine genus with eight-to tensegmented antennae in the queen and worker caste, ten to eleven in the male sex, and the proventriculus with only short sepals. Wheeler also included in the same tribe Aphomomyrmex, Brachymyrmex and Myrmelachista. Emery (1925) redefined Myrmelachistini to include only the two genera Myrmelachista and Stigmacros, both with the female castes with less than twelve antennal segments and a distinct antennal club formed by the three to four terminal segments. He placed Aphomomyrmex, Brachymyrmex, Cladomyrma, Dimorphomyrmex and Gesomyrmex in Dimorphomyrmicini based on the eight-to nine-segmented antennae, the large eyes and the short frontal carinae.
Based on a combination of larval characters Wheeler & Wheeler (1976& Wheeler ( , 1985 included Aphomomyrmex, Brachymyrmex, Cladomyrma and Petalomyrmex in Brachymyrmecini and Myrmelachista in Myrmelachistini. This arrangement in two different tribes excluded Aphomomyrmex+ Cladomyrma + Myrmelachista + Petalomyrmex as a monophyletic group and, furthermore, did not resolve the relationships of these arboreal genera. This is not reflected in Holldobler & Wilson's (1990) classification, where they included Aphomomyrmex, Brachymyrmex, Cladomyrma, Myrmelachista, Petalomyrmex and Pseudaphomomyrmex in the tribe Myrmelachistini and therefore did not exclude a possible monophyletic origin for those genera. Snelling (1979) confirmed, after the examination of one queen syntype of Cladomyrma hewitti and the comparison of it with Petalomyrmex phylax and Aphomomyrmex after, that Cladomyrma and Aphomomyrmex represent distinct ant genera. Snelling did not comment on possible relationships.

Measurements and indices
Morphological terminology in the text follows Holldobler & Wilson (1990).
Alitrunk length (AL). The diagonal length of the alitrunk in profile from the point at which the pronotum meets the cervical shield to the posterior base of the metapleuron.
Head length (HL). The length of the head proper, excluding the mandibles, measured from the mid-point of the anterior c1ypeal margin to the mid-point of the occipital margin, in full-face view.
Head width (HW). The maximum width ofthe head in full-face view, measured below the eyes.
Palp formula (P F). Number of maxillary palp segments followed by number of labial palp segments; e.g. PF 6,4. Scape index (Sl). SLx l00/HW. Scape length (SL). The maximum straight line length of the antennal scape excluding the basal constriction or neck to the condylar bulb.
All measurements are given as minimum, maximum and in parentheses the median, the unit is mrn; e.g. AL 1. 23-1.45 (1.40).
The following characters are of potential significance for the phylogeny of this subfamily, and were used in defining the genus-groups.
Hind coxae. In ventral view, the petiolar insertion either is not extended anterior to an imaginary line between the two anteriorrnost points of the hind coxal cavity (Fig. IB) or reaches anterior to the imaginary line (Figs 2B, 3B; Agosti & Bolton, 1991: Figs 3, 4). In parallel, the hind coxae are closely set in the first (Fig. lA) or widely separted (Fig. 3A). This is obscured when the anterior part of the petiolar cavity is covered with a non-sci erotized membrane (Fig. 2). When the hind coxae are widely separated, the mesocoxae meet medially, forming a If-shaped concavity ( Fig. 3A) to accomodate the petiole when the latter is downflexed.
Ventralside ofthe petiole. In profile the ventral face of the petiole is v-shaped or u-shaped, corresponding to the respective position of the hind coxae.
Functionally the position of the hind coxae and the shape of the ventral side of the petiole seem to be two differently evolved methods for keeping the petiole in a defined position, e.g. during defensive behaviour of Formica species, where the ant is spraying poison gland compounds by pulling the gaster under the ventral side of the alitrunk in the direction of the enemy.
He/dum. The helcium or collar-like pretergite and presternite of the third abdominal segment (Bolton, 1990) is situated either in the tergite, or between tergite and sternite, or in the sternite of the first gastral segment, and is .either simple or bipartite. In the case where the helcium is situated in the tergite, the ventral part of the helcium is separated from the adjacent sternite by a distinct transverse groove, which is easily seen as a brighter strip across the anteriorrnost part of the segment (Fig. 4).
The position of the helcium is, in all genera except Oecophylla, ventral on the anterior face of the first gastral segment. In the Formica genus-group the helcium is never concealed by the segment as is the case in most of the genera of the Lasius and the Pseudolasius genus-group.
First gastral segment. The ventral position of the helcium coincides with three main structural types of the first gastral segment. The Lasiustype ( Fig. 5) has the helcium surrounded by the sternite, but the anteriormost part of the tergite is extended ventrally, so that the lateral sides of the helcium are effectively part of the pretergite

Revision of Cladomyrma 295
and only the ventral side part of the presternite. The gastral tergites conceal the sternites laterally. The Pseudolasius-type ( Fig. 6) has the helcium entirely in the sternite and the first gastral tergite and sternite are anteriorly fused. The gastral tergites and sternites meet laterally. The Formica- (Fig. 4) and Oecophylla-type ( Fig. 7) have the helcium entirely within the first gastral tergite, which is much more extended than the sternite, which is restricted to the ventral face. The helcium of the Oecophylla-type (Fig. 7) is bipartite, with the presternite forming the ventral face. The Formica-type ( Fig. 4) has the helcium separated by a suture from the sternite. The combination of those characters diagnose the following four genus-groups within the Forrnicinae: Oecophylla genus-group DIAGNOSIS. Hind coxae closely set (as in Fig. 1); in profile petiole ventrally v-shaped; helcium bipartite; helcium set medially with the sternite and the tergite of about the same size or ventrally with an enlarged tergite; tergite and sternite not fused anteriorly (Fig. 7).
Formica genus-group DIAGNOSIS. Hind coxae closely set ( Fig. 1); in profile petiole ventrally v-shaped; helcium simple, the sternite separated from the helcium by a suture; helcium set ventrally with an enlarged tergite; tergite and sternite not fused anteriorly (Fig. 4).  tergite which is extended anteriorly to the ventral side of the helcium; tergite and sternite not fused anteriorly (Fig. 5).

Overbeckia, Santschiella, Stigmacros, Pseudostigmacros.
A comparison of the above-described characters with those within the Dolichoderinae, the supposed sister group of the Formicinae, indicates that the Oecophylla type of the first gastral segment and the petiolar articulation which does not reach in front of a line spanned between the two anteriormost points of the hind coxal cavities are the plesiomorphic states. The occurrence of the first gastral structures of the Pseudolasius and the Lasius type might be independently derived as they are present in highly derived dolichoderine genera, such as Frogatella and Turneria, and Bothriomyrmex respectively (S. O. Shattuck, pers. comm.).
This classification contradicts the old system (e.g. Emery, 1925), which has mainly been based on the structure of the proventriculus, from an asepalous state in the Melophorini to a long sepalous state in Camponotini or Formicini (i.e. Euformicinae). The last two tribes are characterized by two different types of proventriculus (Eisner, 1957) inferring that those two structures are not homologous and that possibly there have been further transformations from an asepalous to a sepalous proventriculus. This supports the proposed arrangement, with the Melophorini split between the Formicaand the Lasius-group.
The use of larval characters supports Emery's system, with minor changes (Wheeler & Wheeler, 1976,1985, but a complete assessment of larval characters for the Formicinae needs to be done to understand the main points of discordance. The classification of Holldobler & Wilson (1990) would support the suggested monophyly of those arboreal ants; however, they did not provide a diagnosis for their classification.
The genus groups presented in this paper contradict previous classifications. A complete cladistic analysis of the Formicinae will be provided later. However, the proposed placement of Cladomyrma in the Lasius genus-group and Aphomomyrmex, Myrmelachista and Petalomyrmex in the Pseudolasius genus-group, inferred by the use of the above-mentioned characters, make the monophyly of Aphomomyrmex, Cladomyrma, Myrmelachista and Petalomyrmex highly unlikely.
Within the Lasius genus-group Acropyga could be considered as the possible sister group of Cladomyrma. The similar alitrunk structure and head shape of the workers of species such as Acropyga acutiventris could also be convergences, as a similarly structured alitrunk is also present in some species groups of Camponotus (e.g. subgenus Tanaemyrmex).

DIAGNOSIS
Worker. Arboreal formicine ants with the following diagnostic characters.
1 Dimorphic worker caste (see comments); AL of major workers 0.8-1.7 mm, AL of minor workers 0.6-1.0 mm; robust ants. 2 Foramen magnum set close to the centre of the ventral surface of the head. 3 Mandible with 7 to 9 teeth in minor workers, 4 teeth in major workers. In major workers with an angulate anterior margin (Fig. 8).
Queen. As major worker, but with the following additional diagnostic characters.
Male. Formicine ant with the following diagnostic characters.
1 Of intermediate size between major workers and queens. 2 Mandible pointed, with a small cleft anteriorly (Figs 15, 16).  Comment. The workers of Cladomyrma seem to be strictly dimorphic; nevertheless, in a few cases minor workers have been found having the same head length as the major workers.
Characters given in the phylogenetic section (above) place Cladomyrma in the Lasius genus-group. The combination of eight antennal segments, the club-shaped funiculus including the terminal six segments, the eyes set laterally to the frontal carinae in the worker and female castes (Figs 9-11), the filiform long antennae with nine segments, the scape shorter than the basal three funicular segments and the presence of a distal process of the subgenital plate, reaching ventrally of the genitalia in situ in the male sex (Figs 23-25) differentiate Cladomyrma from all the other Formicinae genera.
Distribution. Cladomyrma is a Malaysian ant genus and has, so far, only been recorded from Borneo and the Malaysian peninsula. The only record from Sumatra (Roepke, 1930) is probably a misidentification of an Acropyga sp., as within the Formicinae only the queens of Acropyga are known to carry mealybugs in their mandibles during the mating flight (Bunzli, 1935;Buschinger et al., 1987;Agosti, unpubl.), and eight antennal segments are also present in some undescribed Acropyga spp. (Agosti, unpubl.). In RNHL some material labeled 'Roepke' from Sumatra is present but none could be identified either as Acropyga or Cladomyrma species.
Biology. Species of Cladomyrma are purely arboreal. The nests are excavated in the internodes of trees and the different species have been found nesting in a single species of either woody climber, Cicryptata in Milletia nieuwenhuisii (Papilionaceae), or tree species: maschwitzi in Crypteronia griffithii (Crypteroniaceae) and mossyna and petalae in Saraca thaipingensis (Caesalpiniaceae) . The nests are actively excavated by the ants themselves (Maschwitz et al., 1989).
Winged sexuals have been found in January, February, April and August to November, but might be produced through the year as during the other months nobody went out to collect Cladomyrma (Maschwitz, pers. comm.). Queens fly at night and are attracted to light but have also been observed in daytime, searching for a nesting place. Maschwitz et al. (1991) described the nesting place searching behaviour of the queens as sphecid wasp-like.
Little is known about the behaviour. The workers generally seem to be shy (Wheeler, 1910;Bolton, pers. comm.;Maschwitz et al., in prep.), but can be very aggressive after disturbance and even cause small irritated spots on the human skin (Maschwitz et al., 1989).
1. Metapleural gland orifice large, engaging the ventrad part of the metapleuron along entire length of the posteriorly directed section of the metapleuron to the articulation of the petiole (as in Fig. 19 almondshaped opening with a dorsoventral diameter the same length as the distance from the ventral side to the margin above the hind coxae; few scattered hairs below the orifice pointing anteriad. 7. Front coxae reaching beyond the anepisternum (as in Fig. 13).

Male. Unknown.
Comment. The type of Dimorphomyrmex andrei was not available for study. Nevertheless, the drawing following the original descriptions is accurate enough to see the elongate head, typical for this species.
The queen and major worker of andrei have a longer head and the clypeus is posteromedially shining and smoother than in cryptata.
Ciandrei, cryptata and maschwitzi all have a wide open metapleural gland orifice in the worker caste, by which they can easily be separated from the other two species.
From the type series of hewiui, only one minor and two major workers are available. The designated lectotype is a major worker and, based on the long head, hewitti is synonymized with andrei. The minor worker of the type series is a Myrmelachista species, and it is doubtful whether it was collected together with the major workers in the internode of a shrub in South-East Asia, as Myrmelachista is restricted to the Neotropics.
Distribution. C.andrei is restricted to Borneo. The known distribution is from the lowland forest up to 1500 m in moss forest.
Biology. All the queen samples have been collected either at light, by fogging, or from an unnamed shrub (Wheeler, 1910), and the workers have either been .collected with the queen in the above-mentioned shrub, or by using a beating tray (D. H. Burckhardt, pers. comm.), in secondary forest.
Alate queen. Anterior part of the head and antennae yellowish, gaster shining, yellowish brown, otherwise body dark brown. Pubescence on the dorsal part of the first two gastral ter-gites thicker, fading on the subsequent tergites, appressed as on the dorsum of the alitrunk. Erect hairs on the propodeum and the dorsal sides of the petiole and first gastral tergite of equal length.
Paratypes .  Comment. Cicryptata differs from andrei by the shorter head in the female caste and the longer alitrunk in the. worker caste. The metapleural gland is wide open, as in andrei but not as in the other species with brown workers, petalae and mossyna.
One queen from Balikpapan has a higher, domed petiole as cryptata.
Distribution. This species is restricted to Borneo and has only been recorded from Sabah,