The Dacetine Ant Genus Pentastruma (Hymenoptera: Formicidae)

The genus Pentastruma was established by Forel (loc. cit. infra) on the basis of a single Taiwanese worker specimen that he described (P. sauteri) as having 5 antennal segnents, a very unusual nmnber even for a nernber of the Dacetini, to which tribe he indicated that it belonged. In several ways, the description read as though based on a depilated species of Smithistruma, and when, several years ago, Dr. Masao Kubota sent specimens of a nearly hairless short-nandibulate dacetine frown Japan, WLB suspected that it tnight be close to Pentastruma sauteri, despite the fact that its antennae displayed the 6-tnerous condition usual in strurnigenite dacetines. Now we have finally discovered the location of the Hans Sauter Collection of Taiwanese ants, in the Instittit ftir Pflanzenschutzforschung (BZA) der Akadetnie der Landwirtschaftswissenschaften der Deutsche Detnokratik Republic in Eberswalde. Through the kind offices of Dr. G. Morge we have been able to borrow sotne critical fortnicid types from the Sauter tnaterial, atnong thetn the unique specitnen of Pentastruma sauteri. This worker proves to be close to the Japanese species received from Dr. Kubota, but it is specifically distinct. It does also have 6 antennotneres, with the nortnal strutnigenite proportions, and not 5 as stated by Forel. In its general fortn, P. sauteri is a rather typical Smithistruma, except for its complete lack of standing or other conspicuous hairs on head, trunk and petiole, and the new Japanese species tnatches it in these respects. It seetns logical that Pentastruma should eventually be tnerged with Smithistruma, but the latter genus is itself not stable at this


Psyche
[June-September time, because new species have been discovered (mostly unpublished) that seem likely to link it with such senior genera as Trichoscapa and Codiomyrmex.
Until more of these new species have been formally described and properly analyzed, no firtn classification of the short-rnandibulate strurnigenites is practicable, it seems best to retain some of the available generic names for now, if only to avoid excessive combinatorial changes as the classification develops.
Accordingly, we retain the name Pentastruma for the time being. We figure for the first time the type species, P. sauteri, and supplement its original description, and we describe a second species, P. canina, frorn Japan, based on all 3 castes.
Measurements and proportions, and their abbreviations, are those standard in papers on Dacetini, e.g., Brown, 1953, Arner. Midl. Nat. 50:7 ft., and1973, Pacific  Worker: Like Smithistruma in size, and form of head, mandibles and remainder of body, including the 6-rnerous antennae; small funicular segments II and II separate and distinct. Clypeus with median tumulus and broadly extended anterolateral apron; anterior margin concave in outline. Mandibles depressed, porrect, with rounded basal larnella and no diasterna, up to 15 acute teeth and denticles of varying length, including small apical tooth. Labrurn with 2 long, tapered lobes, as in Smithistruma.
Body densely reticulate-punctulate and opaque (feebly shining in some views), but postpetiolar disc and gaster smooth and shining, except for basigastric costulae. Head, trunk, petiole and appendages without erect hairs, and even the pubescence reduced to a virtually invisible (at 50) dilute vestiture of minute, appressed to decurnbent hairs. The under-mouthparts have some small standing hairs. Postpetiole and gaster with a few short, blunt-tipped or remiforrn, standing hairs, mostly arranged symmetrically. Color testaceous to light ferruginous.
Queen: Like the Smithistruma queen, but with differences corresponding to those of the worker. Thoracic dorsurn with a few short, slender but stiff, erect hairs. Pronoturn with a flat, C-shaped, rnarginate dorsal platforn; scutun rising abruptly above this.
Male: As in Smithistruma. Distribution as known: Japan (Honshu and southward); Taiwan.
Alnost certainly occurs on the Asian nainland, but not yet collected there. The figure shows well the full-face outline view of head and mandibles. The head is shorter, with vertex more convex, than in P. canina, and the mandibles are shorter and more "set into" the anterior clypeal concavity. Although we have been unable to view the mandibular dentition directly and in detail in the lone holotype specimen, it seems that a rounded basal larnella is present, and that a series of sharp teeth follows without a diastema. The nmnber of teeth (12?) may be slightly smaller than in P. eanina, and the sizes of the teeth seern to be more evenly graded.
Viewed from the side, P. sauteri is much as shown in the side view of P. canina (Fig. 4), except that in sauteri, the upper vertex is more prominent, so that the head is thicker at this point dorsoventrally, and the transition from frontal to occipital faces of vertex more abrupt. The truncal dorsmn is more strongly sinuate in side view; the propodeal teeth are also shorter and less acute than in canina, and the propodeal larnella wider. The erect pilosity of the gastric dorsurn and apex is even more reduced, in hair number and size, than in canina. In the sauteri type, the middle of the mesopleura is weakly shining, though still sculptured, and the dorsolateral margins of the trunk are cornpletely lacking. P. sauteri still remains known only from this single specimen frotn Habitus as shown for the paratype in Figs. 2 and 4. Note the depressed, flat mandibles and the 6-rnerous antennae, with segments proportioned as in Smithistruma, and also the broadly extended, sharp-edged, larnelliforrn, free lateral rnargins of the clypeus, translucent in bright light. Mandibular armament shown in detail in Fig.  3. After the broadly rounded basal larnella there follow without a diasterna 15 teeth, of which the first, fifth, and ninth are the longest.
Between these, 2 groups of 3 smaller teeth each, in each such triplet, the middle tooth a little longer than the 2 flanking it. A similar triplet follows the ninth tooth, and after this 2 small subapical teeth and a robust apical tooth. Labral lobes at rest extending beyond the rnidlength of the mandibles. Mandibular surface very finely sculptured, weakly sericeous-shining.
Pronoturn with rounded, strongly rnarginate anterior margin (excluding cervix), faintly indicated but rounded humeri, feebly tnarginate or subrnarginate dorsolateral margins, widest (W about 0.31 rnrn) behind rnidlength, tapering caudad into subparallel-sided posterior half of trunk (W about 0.16 mrn across propodeal dorsurn), which even widens again very slightly caudad. Metanotal groove obsolete or nearly so as viewed from above; propodeal teeth approxinately parallel. Faint margins extend the length of the dorsolateral borders of the trunk, but these are visible only in certain views and lights.
Petiolar node subquadrate (rounded in front), slightly wider (W about 0.15 rnrn) than long, its dorsal surface with sculpture partly effaced, weakly shining. Postpetiolar disc transversely elliptical, nearly twice as wide as long (L 0.15, W 0.27 rnrn), smooth and shining, with a widely spaced pair of inclined hairs near posterior border. Gaster with weak basidorsal costulae, effaced rnesad, the longest extending about a quarter of the length of the first tergum.
Erect, feebly enlarged hairs: 4 near base of first gastric tergite, a pair near rnidlength, and a pair near posterior border of first tergite; remaining segments with 2 or 4 hairs each on tergites, and a few fine ventral, erect hairs also on apical half of gaster. The fine, short, extremely dilute, appressed and decurnbent pubescence is invisible except at high magnifications (over 50) and in special, strong lights, and is best developed on mandibles, antennae, vertex, legs, and gaster, though nowhere evident without a special effort to find it.
Color rnediurn testaceous; spongiforn apendages sordid whitishtestaceous. With the usual differences frotn the worker. Pronotutn with flat dorsal pronotal platfortn, as seen from above, tnarkedly constricted before it joins the tnesothorax. Scutellutn rounded and bulging caudad. Petiolar node broader than in worker, and tending to be tnedially sulcate in front. Scututn irregularly reticulate-punctate, its surface weakly shining in sorne lights, opaque in others. Color testaceous to medium ferruginous, usually slightly darker than worker.
Color blackish-brown, gaster dark reddish-brown, legs and antennae sordid, pale, dull brown; wings hyaline. Mandibles slender, each with a weak tooth-like angle apicad of midlength, only slightly curved, probably not opposable, tapered to a very acute apex. Labrutn broad, the 2 lobes short and separately rounded.
Antennal scape broader and longer than pedicel, and about as broad as the apical antennal segrnent; segrnents III through XII slender and cylindrical, all longer than scape or pedicel. Pronotutn forrning a flattened, C-shaped platforrn, sornething like that of female. Mesonotum large and bulging; notauli present but short, and not rneeting behind to fortn a V or Y; parapsidal lines present.
Scutellurn bulging, rounded caudad. Propodeal teeth low, subacute, with narrow, concave infradental larnellae. Mesokatepisternutn and a patch on the side of the propodeum with sculpture effaced, nearly or quite stnooth and shining. Petiole clavifortn, with low, rounded, scarcely differentiated node that is rnainly stnooth and shining above; spongiforrn appendages reduced to a narrow rnid-ventral strip and a fine, cariniforrn posterodorsal collar. Postpetiole broader than long, rounded, srnooth and shining, with a narrow, posterior collar of transparent larnella and an anteroventral spur trirnrned narrowly with transparent lamella. Gaster unadorned at base, smooth and shining, with an extretnely sparse, inconspicuous sprinkling of tiny, appressed The variation of worker paratypes is tnost tnarked in body size, relative head width, acuteness and width of propodeal teeth and trailing latnellae, and in depth of ferruginous coloration, often varying to faded straw color (in callows?). TL 2.5-2.9, HL 0.68-0.78, HW 0.48-0.56, ML 0.14-0.16, Eye L 0.04-0.06, WL 0.62-0.72 tmn; CI 66-74 (tnean 71 for n 16), MI 19-22. P. canina, widespread in central and southern Japan, is readily distinguishable frotn P. sauteri by the forn of the head and tnandibles (Figs. and 2). Frotn the known Smithistruma and Trichoscapa species of eastern Asia, the canina worker tnay be separated by its head shape and by the total lack of standing pilosity on head, scapes and trunk.
Dr. Masao Kubota, of Odawara, Kanagawa Prefecture, Japan, deserves thanks, not only for the opportunity to study the many excellently prepared specimens of P. can&a, but also for notes on the biology of the species summarized below. P. canina is an uncommon species, found in the Kant6 District and southward. It inhabits the floor of coastal evergreen broadleafed forest, which is generally subtropical. Nests are found in small pieces of rotten wood, rotten fallen branches, under moist leaf litter, or at a slight depth in the humus. The largest colony censused contained one queen and 57 workers.