Pilotrochus besmerus, Brown, W. L., 1978

Brown, W. L., 1978, An aberrant new genus of myrmicine ant from Madagascar., Psyche 84, pp. 218-224 : 221-224

Pilotrochus besmerus new species

Figs. 1,2.

Holotype worker: Total length (TL) 2.9, head length (HL) 0.68, head width (HW) 0.60, mandibles extend beyond median clypeal free margin (ML) 0.11 mm; when head is tilted back a little from full-face view, mandibles may extend beyond clypeus as much as 0.18 mm; trunk length (WL) 0.64, scape L (excluding radicle) 0.32, greatest length of eye 0.07 mm. Petiole length (chord of arc) 0.45, hind femur length 0.43, hind tibia length 0.34, hind tarsus length 0.60 mm, of which metatarsus is half.

Details of form and sculpture are well shown in the figures. As seen in dorsal view, eyes hidden in full-face view, barely visible when head is tilted back slightly, as in fig. 1. Pronotum slightly broader than long (width 0.38 mm), rounded in front, excised behind; mesonotum subquadratic, about 0.20 mm wide, with feebly convex borders on all four sides. Petiolar node 0.17 mm wide, postpetiolar node with rounded sides, slightly wider behind (width 0.21 mm, length 0.20 mm).

Pronotum smooth and shining, with about 10 costulae running longitudinally at different lengths; mesonotum with 5 longitudinal costulae on rugulae. About 5 longitudinal rugules each on petiolar and postpetiolar nodes, but weaker on the postpetiole, so that its disc is primarily smooth and shining like the gaster.

Hairs mostly a little less than 0.1 mm long on anterior head and scapes, a little more than 0.1 mm on posterior vertex; 0.15 - 0.25 on trunk, petiole, postpetiole and gaster, becoming shorter again at gastric apex; about 0.1 to about 0.3 mm on legs; flagelliform, many with tips reflexed or even looped back.

Holotype (Museum of Comparative Zoology at Harvard University) a unique worker taken in a Berlese sample of forest humus and litter from along the road to Anosibe, 33 km south of Mora-manga, in east central Madagascar, 4 - 12 April 1975 (A. Peyrieras).

The relationships of Pilotrochus are obscure. The shape of the head, with its broad and deep scrobes and small ventrolateral eyes, recalls that of Dacetinops , or the Codiomyrmex group of Dacetini , or even Tatuidris , but Pilotrochus differs strongly from all of these in its 8 - segmented antennae, in the form of its mandibles and their teeth, and in the form of its trunk and petiole. The lateral " hairwheel " organs are also striking, and so far as I am aware are unmatched among the ants, although the region of the ventral furrow between pro- and mesothorax is sometimes modified and apparently glandular in some dacetines and a few other myrmicines.

The 2 - segmented antennal club, together with some points of habitus (especially coarse sculpture and long, flexuous pilosity, plus the antennal scrobes), recalls the neotropical genus Lachnomyrmex , but the shape of the trunk in Pilotrochus is completely different, the propodeal teeth so prominent in Lachnomyrmex are completely absent, and the mandibles in the two genera are very different.

At the moment, all one can say without seeing the winged forms and larvae of Pilotrochus , and without knowing something of its lifeway, is that it is a member of subfamily Myrmicinae , but one not belonging to any of the well-circumscribed " higher " tribes ( Crematogastrini , Dacetini , Basicerotini , Cataulacini , Attini , etc.). Thus, it falls among the mass of generic complexes related to Myrmica , Pheidole , Myrmecina , Rogeria , etc., among which tribal boundaries are impossible to define for the present, or at least are in dispute.

Considering the revisionary work that must be done before we have a rational tribal classification of Myrmicinae , it seems to me that nothing would be gained by erecting a new tribe for Pilotrochus , even though for the time being I am able to fit it comfortably into any existing myrmicine tribe.

The generic name is derived from the Greek ' pilos' (hair) + ' tro-chos' (wheel), while the specific name besmerus combines the Latin ' bes' (eight of twelve) with the Greek ' meros' (part), in reference to the 8 - segmented antennae as compared to the primitive myrmicine (and formicid) 12 - merous condition.