Opamyrma, Yamane, S., Bui, T. V. & Eguchi, K., 2008

Yamane, S., Bui, T. V. & Eguchi, K., 2008, Opamyrma hungvuong, a new genus and species of ant related to Apomyrma (Hymenoptera: Formicidae: Amblyoponinae), Zootaxa 1767, pp. 55-63 : 56

Opamyrma gen. n.

(Figs. 1-12)

Type species. Opamyrma hungvuong sp. n.

Worker description. Preoccipital carina complete, almost encircling the head slightly before its posterior margin (“poc” in Fig. 4). Venter of head with a distinct and complete median furrow, with each anterolateral corner forming a process (“alc” in Fig. 3). Clypeus posteriorly margined with a distinct continuous carina (“pcc” in Fig. 3); median part of clypeus rather clearly divided into posterior horizontal portion and anterior steep slope; the posterior portion broadly inserted between antennal sockets, extending anteriorly to the level of posterior margin of the sockets; lateral part of clypeus narrow from front to back. Mandibular base with closed trulleum (“trl” in Fig. 3). Labrum on its outer face with at least two rows of peg-like denticles, each with more than 10 denticles (“lpd” in Fig. 3). Eye absent. Frontal lobe absent. Antennal sockets completely exposed in full-face view, directing almost dorsad, located in a large, roundly excavated area whose anterior wall is steep just behind the posterior margin of clypeus; the area not clearly defined posteriorly. Antenna 12- segmented, gradually incrassate from segment II to XII.

Mesosoma elongate, with a single furrow (“msf” in Figs. 6 & 7) which is deep and flexible and separates pronotum from the remaining part of mesosoma. Metapleural gland bulla round, occupying posterior twofifths of ventrolateral part of the pleuron; metapleural trench running below the bulla. Junction of dorsal and posterior faces of propodeum round without any transverse carina; posterior face of propodeum laterally without spines/carinae. Propodeal spiracle situated relatively low on the side of propodeum, near the weak furrow separating metapleuron from lateral side of propodeum. Propodeal lobe present, low and round.

Mid- and hind tibiae each with a reduced barbulate anterior spur (“ats” in Fig. 8) and a well-developed pectinate posterior spur (“pts” in Fig. 8). Pretarsal claws simple, without teeth.

Waist consisting of a single segment (petiole); petiole elongate, narrowly attached to abdominal segment III (gastral segment I), virtually without anterior peduncle; tergo-sternal sutures of petiole present as longitudinal furrows on ventrolateral edges that meet medially at 1/3 length of petiole from the base (“tss” in Fig. 10); the sternite of petiole reduced to a small posteroventral sclerite, bounded by the conspicuous tergo-sternal sutures; petiolar spiracle located anteriorly on the lateral face of petiole at its mid-height.

Gaster very long, laterally compressed, especially in posterior portion, in profile highest at the posterior end of abdominal segment VI (“absg-VI” in Fig. 11). Segment III (“absg-III” in Fig. 11) seen from above longer than broad, narrowed basally, longer than segments I V, V and VI, having a free anterior face above the helcium; anteriormost part of abdominal sternite III (“abs-III” in Fig.11) produced anteriad to the same level as the anteriormost part of tergite III (“abt-III” in Fig. 11). Segment IV with differentiated presternite (“ps-IV” in Fig. 11). Spiracles on segments V -VII concealed by the preceding segments. Segment VII (“absg-VII” in Fig. 11) longest among the segments III -VII. Pygidium (“abt-VII” in Fig. 11) and hypopygium (“abs-VII” in Fig. 11) unarmed.

Discussion

Opamyrma is similar to Apomyrma with several shared characteristics: the outer face of the labrum bears peglike teeth; the frontal lobe is absent; the antennal socket is directed almost dorsad; the sternite of the petiole is reduced to a small posteroventral sclerite, bounded by the conspicuous tergo-sternal sutures; and the third abdominal segment above the helcium has a free anterior face. All this may support the inclusion of the new genus within the separate tribe Apomyrmini with Apomyrma (but see below for the current status of this tribe).

The features which support the erection of the new genus Opamyrma independent of Apomyrma (see Brown et al 1971; Bolton 1990, 2003 for characterization of Apomyrma ) are: preoccipital carina complete, almost encircling the head slightly before its posterior margin; clypeus posteriorly margined with a distinct continuous carina; petiole without a distinct anterior peduncle; abdominal segment III longer than I V, V and VI; segment VII longest among the segments III -VII; anteriormost part of abdominal sternite III produced anteriad to the same level as the anteriormost part of tergite III; segment IV with differentiated presternite.

Opamyrma also shares some features with members of Leptanillinae , which, however, clearly differ from all the amblyoponines sensu Saux et al. (2004) in having a 2-segmented waist. For example, the morphology of clypeus resembles that of Protanilla and Anomalomyrma , and the structure of the metapleural gland orifice and its surroundings is also rather similar to that seen in Leptanillinae . The extremely hypertrophied pygidium of Opamyrma also reminds us of the condition in some leptanillines.

The complicated history summarized below indicates the difficulty in deciding the systematic position of Apomyrma . Apomyrma was established as a monotypic genus under the subfamily Ponerinae by Brown et al. (1971) from Ivory Coast (Afrotropical region). Wheeler and Wheeler (1985) placed it under the tribe Amblyoponini of Ponerinae, and later Dlussky & Fedoseeva (1988) established the tribe Apomyrmini under Ponerinae. However, Bolton (1990) transferred Apomyrmini to Leptanillinae listing 16 characteristics shared by the traditional Leptanillinae and Apomyrma (but only with the size and location of the spiracle on abdominal segment III as apomorphies), and then Baroni Urbani et al. (1992) established the subfamily Apomyrminae . Bolton(2003), in his morphology-based classification of the family Formicidae, followed their treatment. More recently Saux et al. (2004), based on their molecular phylogenetic analysis, placed the genus under the subfamily Amblyoponinae , and partly modified Bolton's (2003) definition of Amblyoponinae . Although the three recent molecular analyses of these taxa (Saux et al. 2004, Moreau et al. 2006, Brady, et al. 2006) all gave different results, in each of them Apomyrma is the sister group of one or more genera of Amblyoponinae sensu Bolton (2003).

As mentioned above, and also as pointed out by Ward (2007), Apomyrma has some similarities in morphology and behavior with both Leptanillinae and Amblyoponinae (see also Brown et al. 1971, Bolton, 1990, Masuko 1990, Ward 1994). The discovery of the new genus Opamyrma would further require a reexamination of the relationship of these two subfamilies, since Opamyrma possesses additional features shared with Leptanillinae . Here we do not intend to propose any new classification system in which the position of this new genus is appropriately settled. Here Opamyrma is tentatively placed in Amblyoponinae . Since the resolution within Amblyponinae is still insufficient to address relationships among the genera (Saux et al., 2004), we follow the single tribe-rank classification for this subfamily.