Probolomyrmex, Taylor, R. W., 1965

Taylor, R. W., 1965, A monographic revision of the rare tropicopolitan ant genus Probolomyrmex Mayr (Hymenoptera: Formicidae)., Transactions of the Royal Entomological Society of London 117, pp. 345-365 : 363-364

VI. A Species Properly Excluded from Probolomyrmex : (?) Leptanilla palauensis (M. R. Smith) , comb. n.

Probolomyrmex palauensis M. R. Smith , 1953, J. N. Y. ent. Soc. 61: 127 - 129, figs. 1 - 2. [[ male ]]. Type locality: S. W. of Ulimang, Babelthaup I., Palau Islands, Micronesia. Holotype: United States National Museum (examined).

This species was described from a single male collected without associated workers or queens. The general habitus is somewhat like that of the female castes of Probolomyrmex , but knowledge of the male of P. greavesi precludes the possibility that palauensis belongs in that genus.

A completely satisfactory generic assignment for palauensisis not possible at present. Inclusion in the Formicidae is acceptable on the basis of the nodal form and other general characters, although metapleural glands are not visible on the specimen. The presence of these organs is apparently a universal and definitive character in female ants, but their presence among the males has never been objectively surveyed. A spot check in the Museum of Comparative Zoology collection shows that metapleural glands are lacking, or externally indiscernible, in the males of many genera. Placement in the subfamily Ponerinae is not tenable, since all known ponerine ants, of all castes, have the tergum and sternum of the second post-petiolar (fourth true abdominal) segment fused laterally to form a strong tubular structure and this is not so in the holotype of palauensis .

I have concluded that a queried assignment to the genus Leptanilla (subfamily Leptanillinae ) provides the best placement for palauensis . A number of male-based species have been described in Leptanilla or in the possibly synonymous genus Phaulomyrma by Santschi (1907, 1908) and by G. C. & E. W. Wheeler (1930). However, none of the known leptanilline males were collected in definite association with workers, and until such specimens are available the status of the Wheeler and Santschi species must be questioned. The only presumed leptanilline male available here for comparison with palauensis is the holotype of Phaulomyrma javana Wheeler and Wheeler. The two specimens agree sufficiently well for relationship between them to be reasonably assumed: if Phaulomyrma is truly a leptanilline ant, then palauensis probably is also.

The holotype of palauensis resembles the presumed Leptanilla-Phaulomyrma males in the following features:

(1) The structure of the head, mandibles, frontoclypeal region, antennae, eyes and ocelJi. The oral palpi are unfortunately not visible in palauensis .

(2) The torn wing fragments appear to have had extremely reduced venation, as in the leptanillines.

(3) The presence of one apical spur on the middle tibia and two on the posterior one, a feature characteristic of several of the described " Leptanilla " males.

(4) Fusion of the lateral mesosomal sclerites is more marked in palauensis than in the leptanillines, but the form of this tagma and of the petiole and gaster, is similar.

(5) The apparent absence of metapleural glands, which are not visible in the slidemounted type of Phaulomyrma , even under phase-contrast examination.

(6) Workers and queens of available Leptanilla species do not have the sclerites of the fourth abdominal segment fused laterally. This is so in the Phaulomyrma male, and apparently also in the described Leptanilla males, as well as in the type of palauensis .

(7) The peculiar structure of the terminalia, especially that of the much enlarged non-retractile genital capsule, with its greatly elongated aedeagus. Wheeler & Wheeler (1930: fig. 2 c) show a ventral view of the genital capsule of Phaulomyrma . In the specimen illustrated the apices of the gonoforceps are folded inwards in an apparently unnatural position; if they were unfolded the genital apex would closely resemble that of palauensis , as shown in Smith's figure 2. A similar folding of the gonoforceps evidently occurred in the specimens illustrated by Santschi, and with appropriate correction they too would resemble palauensis .

According to the diagnoses of Wheeler & Wheeler (1930), palauensis appears closer to Phaulomyrma in some features than to Leptanilla . However, placement of this species in Leptanilla seems sensible in view of the uncertainty surrounding the status of all these forms.