William L. Brown, Jr. and Walter W. Kempf.
A Revision of the Neotropical Dacetine Ant Genus Acanthognathus (Hymenoptera: Formicidae).
Psyche 76:87-109, 1969.

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PSYCHE
Vol. 76 June, 1969 No. 2
A REVISION OF THE NEOTROPICAL DACETINE
ANT GENUS ACANTHOGNAT'HUS
(HYMENOPTERA: FORMICIDAE
BY WILLIAM L. BROWN, JR.~ and WALTER W. KEMPF' At the time it was last reviewed (by M. R. Smith in 1g44), Acanthognathus contained three species: ocellatus, lentus and brevicornis, known from Central America and a few localities along the eastern edge of South America. In the present paper we are able to add three distinctive new species-one from the heart of Amazonia, one from the Pacific Slope of Colombia, and one from Southeastern Brasil; and a male of the genus is described for the first time. We present fragmentary observations on living colonies of A. rudk and A. ocellatus to confirm M. R. Smith's surmise that the genus is predaceous, at least to some extent on Collembola. Acanthognathus is a very distinctive genus within the tribe Dacetini, to which it dearly belongs, and within which it is one of the two most primitive living genera (Brown and Wilson, 1959). The other primitive member is Daceton, containing a single spectacular species confined to hylaean South America (Wilson, I 962). Though Daceton and Acanthognathus workers share a number of primitive characters (antenna1 segments I I ; palpal segments 5, 3 ; compound eyes large; antenna! scrobes absent; humeri armed), they are very different in size, habitus, and choice of nest site, and thus may have diverged a long time ago. Acanthognathus has the aspect of a genus that has begun a shift from epigaeic to cryptic foraging. Its retention of large eyes, multisegmented antennae and palpi, and long mandibles suggests that much of its foraging must still be done in the open, department of Entomology and Limnology, New York State College of Agriculture at Cornell University, Ithaca, New York 14850, USA. 'Convento de Sio Francisco, Caixa Postal 5,650, Siio Paulo, S. P., Brasil. Manuscript received by the editor January 2,1969



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Psyche
Figures 1 - 3.
Acanthognathus spp., workers from type series in outline, sculpture and most pilosity omitted. Fig. 1, A. rudis sp. n. from type locality (Jardim Botanico, Agua Funda, Siio Paulo), dorsal view of head and mandibles. Fig. 2, A. rudis (Guararema, SGo Paulo), petiole and postpetiole from side. Fig. 3, A. stipulosus sp. n., holotype petiole and postpetiole in side view. Fig. 1 drawn by Brown, Figs. 2 and 3 by Kempf and Brown.




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19691 Brown and KempfÌ Acanthognathus 89 even though its nests tend to be cryptically situated in the ground or rotten wood. Like most or all Orectognathus, the related Australian genus, its species probably forage mainly at night. Acanthognathus Mayr, 1887:578. Type species A(anthognathus ocellatus, monobasic.
Acanthognathus: Emery, 1922, Gen. Insect., I74c :3l7-3 18.- M. R. Smith, 1944:150-152, key to spp.- Brown, 1948:125, in generic key.- Brown and Wilson, 1959 :28 1-283, phylogeny, biology. Worker: Size small (TL 3.5-4.6 mm). Habitus of strumigeni- form Dacetini, i.e., with head much longer than broad, more or less depressed dorsoventrally, and much narrowed and drawn out anteriad, with a deep posterior excision (Figs. I, I I ) ; mandibles greatly elongate, narrow and linear, straight or nearly so, each with 3 spini- form apical teeth. Somewhat beyond the midlength of each mandible, there is often a small welt 01- convexity on the inner margin, whence issues a long, fine hair, the trigger hair, which lies flat against the margin when the mandible is closed, but which stands erect when the mandible is open, pointing straight forward, and serving as a tactile range-finder. Preapical teeth or denticles also occur on the mandibles of some species. Near the base of each mandible a long, slender basal process arises from its ventral surface and runs obliquely basoventrad, crossing its opposite number when the mandibles are closed (Fig. I) ; the apices of these processes are split into a pair of short acute teeth, by means of which they engage one another when serving as props to hold the mandibles widely open. (The basal pro- cesses have also been observed by Moeller and ourselves to be used in carrying brood in d i s and ocellatus, with mandibles opened widely. )
Frontal lobes form small convex shields over the antennal inser- tions. Eyes large, near or slightly in front of middle of sides of head, only moderately convex, normally with 40 to 70 or more facets. Clypeus narrowly bell-shaped, flat, with long posterior lobe inserted between frontal lobes. Antennae long and slender, 11- segmented (Figs. I ,4, s s ) , with the scapes oddly bent and usually constricted near apex. Small antennal segments III through IX in a rigid straight line, and may sometimes be fused internally, cor- responding (as Santschi has already pointed out) to the long segment I11 in the Australasian genus Orectognc~~hzis. Antenna1 scrobes lacking. Occipital area deeply and broadly concave, set off from vertex by a sharply rounded angle.




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90 Psyche [June
Maxilla with 5, labium with 3 segments in each palpus. Labrum reduced to a small piece shaped like an inverted V. Truncus strongly constricted and deeply impressed at metanotal groove; pro- and mesonotum fused together; humeral angles dis- tinct and often more or less toothlike. Propodeum armed with a pair of slender oblique spines; declivity flat or weakly concave, smooth, at most feebly carinate on sides ; inferior propodeal plates small, subacutely angled to rounded; propodeal spiracles circular, situated close under the bases of the spines, directed posterolaterad; atrum of ~netapleural gland with dark borders visible through in- tegument, large, elliptical, oblique. Petiole with a long, slender, anteriorly tapered peduncle in front, a distinct, at least discally smooth and shining node, and a short posterior peduncle (Figs. 2-4). Postpetiole rounded, not very different in width from petiolar node, smooth and shining, at least on summit. No spongiform tissues on nodes or elsewhere. Gaster broadly oval, smooth and shining. Legs long and slender, femora moderately incrassate in apical half; no spurs on middle and posterior tibiae; claws slender, simple. Sting
slender, rigid, with very acute tip ; exsertile, functional. Sculpture ranging from almost entirely smooth and shining (teledectus) to rugulose and opaque over dorsum of head and truncus (rudis), with at least some coarse but shallow, round tuberculate fossae on the head, and often a few on promesonotum as well. The tubercles of these fossae often each bear a single, short, slender, curved or reclinate clavate hair, these clavate hairs also more or less generally distributed over scapes, mandibles, femora and tibiae, promesonotum, propodeal spines, posterodorsal faces of both nodes, and sometimes underside of head. Short fine erect or reclinate hairs on mandibular apices, funiculi of antennae, tarsi and gastric apex; gastric dorsum also with very sparse, fine, short appressed hairs. Color prevailingly ferruginous.
Queen: Similar to worker in size and proportions, but with 3 ocelli, larger compound eyes, and the usual differences due to the prenuptial presence of well-developed wings and thoracic flight sclerites. Scutellum prominent and convex, propodeal spines well- developed and acute, but stouter than in worker. Male (known only for A. rudis, Figs. 5-10) : Habitus dacetine, but slender; node long and low; sculpture mostly smooth and shining with fine punctures. Mandibles reduced to minute rounded lobes, each with a single acute tooth; separated by labrum, which is larger than mandibles and has a lobe at each free corner, just above the



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Brown and KernpfÌÔA~antho~nathu
91




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slightly projecting, single-segmented labial palpi. Maxillary palpi
not seen in undissected mouth-parts, presumably reduced to a single small segment. Antennae long, 12-segmented; scape and pedicel subequal in length, each about twice as long as broad; flagellum filiform, only very slightly thicker at apex than at base. Compound eyes large and strongly convex, placed near the front of the sides and occupying about half the sides. Ocelli prominent, raised, sur- rounding a prominent indentation in the vertex. Truncus well-developed, mesonoturn with weak parapsidal furrows and notauli, the latter incomplete, not or at least not distinctly fused behind. Pronoturn and propodeum unarmed, rounded; inferior pro- podeal plates present.
Wings long, densely microtrichiate ; apical margin of fore wing and apical and hind margins of hind wing with a wide fringe of fine hairs.
Legs slender, long; tarsal claws simple, short, fine; tibiae of mid- dle and hind legs without apical spurs.
Genitalia (Figs. 8-10) formed on the same plan as Stmigenys; aedeagus valves subtruncate apically, cuspis of volsella slender ; mesa1 face of paramere broadly excavated opposite volsella. Hypopygium elongate-triangular, with concave sides tapering to a narrowly rounded apex.
Pilosity abundant and widely distributed, consisting of short, fine soft brown hairs, mostly decumbent, but erect on propodeum. Color dark brown to probably blackish in fully-colored specimens; ap- pendages pale.
Larva: To be described separately by G. C. and J. Wheeler. As now known from definite records, Acanthognathus ranges from Honduras in the north to Rio Grande do Sul in the south. It seems very likely that its range reaches into northeastern Argentina and to Bolivia, and it would not be surprising to find the genus in southern Mexico. Two of the new species described here extend the records into the Amazonian heartland and to Trans-Andean Colombia, while a new collection of A. ocellatus is the first for the genus from Trinidad.
The great increase in collections of Acanthognathus in recent years is due in large part to the rise in use of the Berlese funnel and similar methods of extraction of forest soil and litter, as well as to more intensive collecting in rotting twigs and similar microhabitats on the



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19691 Brown and Kempf - Acanthognathus 93 floor of tropical forests. All of the samples for which we have ecological data came from moist or wet forest of the tropical or subtropical type. Nests of isolated (possibly nest-founding) dealate queens of brevicornis, lentus, ocellatus and rudis have usually been taken in rotten twigs or small pieces of rotting wood in forest litter. The colonies are small, often with only 10-20 or fewer adult workers, and no nests with more than about 30 workers have been seen. Usually there is a single dealate queen per nest, though two have been found in a nest of A. rudis from Siio Paulo. The nests resemble greatly those of certain long-mandibulate Strumigenys, as already noted by Mann (1922), and like Strumigenys, the hnthognathus workers and queen move slowly and often curl up to play dead when jarred.
An observation of Moeller, repeated by Emery ( I 922) and others, showed that workers use the basal processes of the mandibles to carry their brood. We have been able to confirm this activity for A. ocellatus and A. rudis in captive colonies. We have also observed these same two species to capture, by means of a snap of the mandibles, entomobryid Collembola that were placed in the artificial nest with them. A colony of A. ocellatus from Cerro Carnpana Panama, fed a newly-captured entomobryid to a larva, after the fashion of Strumigenys. Limited tests of other small, soft-bodied arthropods were tried with both ocellatus and rudis, and though none of these was captured or even approached, the trials were too few to establish the breadth of prey specificity. Foraging workers of these two species, and the holotype of A. teledectus before its capture in the leaf litter, held their mandibles open to about 180å when threatened or when approaching prey. This is apparently accomplished by locking to- gether the apices of the opposed basal processes, but the details are not altogether clear, especially the role, if any, of the labrum in the process. As with Strumigenys, the sting is employed to quiet strug- gling prey.
A worker of A. ocellatus taken by Mark! on Trinidad is accom- panied by the note, "at night," indicating what the relatively large eyes suggest- that foraging is epigaeic, perhaps subarboreal, and largely crepuscular or even nocturnal. The similar Austi-alasian genus Orectognathus appears to follow this foraging pattern. THE SPECIES
Acanthognathus comprises six known species, of which five are very distinct, and one, A. lentus, is kept separate from A. ocelZatus with doubt for the time being.




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94 Psyche [June
The descriptions and measurements (Table I) utilize some ab- breviations kept standard in recent works on ants, particularly the tribe Dacetini. HL is the length of the head in full-face (dorsal) view, including occipital lobes and the entire clypeus. HW is the maximum measurable width of the head in full-face view. CI is cephalic index, or HW/HL X 100. ML is the exposed length of the closed mandibles beyond clypeal margin measured in full-face view. SL is the chord length of the antenna1 scape; SI (scape index) is SL/HW X 100. MI is the mandibulo-cephalic index, or ML/HL X 100. SMI, scape-mandibular index, is SL/ML X 100. All measurements are in millimeters, and have an approximate error of å 0.01 mm.
Abbreviations for the main collections in which deposit has been made are: (MCZ) Museum of Comparative Zoology, Harvard University, Cambridge, Massachusetts 02 138, USA; (USNM) United States National Museum, Washington, D. C. 20560, USA; (WWK) Collection of W. W. Kempf, including the Collection of Thomas Borgmeier, Caixa Postal 5,650, Siio Paulo, S. P. Brasil; ( DZSP) Departamento de Zoologia, Caixa Postal 7 I 72, Siio Paulo, Brasil. Other coIlections are given in full. The species are listed in alphabetical order.
Acanthognathus brevicornis
Acanthognathus brevicornis M. R. Smith, 1944: 150-152, worker, dealate queen. Type loc.; Barro Colorado Island, Panama Canal Zone. Holo- type worker and paratype queen in USNM; paratype queens in MCZ- Kempf, 1964:67, worker from Nova Petropolis, Rio Grande do Sul, Brasil.
Worker and queen: Distinguishable from the similar A. oceZZatus (see below) by 2 main characters :
I. Scapes shorter than those of other species of the same size; scape length (chord) about equal to head width in the worker, less in the queen (see Table I). Scape length markedly less than mandible length in both worker and queen; all other species have scapes as long as or longer than mandibles, except A. teledectus with its extra- ordinarily long mandibles.
2. Mandibles (0.86 mm long in holotype worker, teste Smith) with noticeable submedian welt on inner borders and 2-5 irregular, separated low denticles or minute tubercles in the space between the welt and the apical teeth on each mandible. No other species has these denticles so far as known.
In addition, the sculpture of A. brevicornis is more strongly effaced, more shining than in A. ocellatus, but not as much so as in A.



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19691 Brown and Kempf - A canthognathus 9 5 teledectus.
The brevicornis fossae on head and alitrunk tend to be smaller, shallower and more widely spaced, with interspaces cor- respondingly broader, smoother and more shining. Male unknown.
Material examined (in addition to type series- I worker and 3 queens from Panama Canal Zone) : BRASIL: State of Rio Grande do Sul:
Nova Petropolis, September 1959, F. Plaumann leg., I worker ( WWK) ; Morro Reuter, December 1964, F. Plaumann leg., I dealate queen (WWK). State of Para: Utinga Forest Tract, near Belkm, g August 1962, P. F. Darlington leg., dealate queen from hollow rotten twig on rain forest floor (MCZ) . Acanthognathus lentus
Acanthognathus lentus Mann, 1922:34-35, fig. 16, worker, queen. Type loc.: Progreso, Honduras. Syntypes in MCZ, USNM, WWK. Worker and queen: Measurements and proportions given in Table I, closely overlapping those of A. ocellatus, fossae of dorsum of head larger and more crowded, with some rugulae present between them even on the posterior half, weakly shining ; extreme posterior corners of cephalic dorsum smooth and shining. Otherwise very similar to A. ocellatus.
A. lentus probably is only a local sculptural variant of A. ocellatus. The scanty material available does not yet wholly bridge the differ- ence, but a Trinidad specimen of ocellatus (q.v.) shows a tendency to do so.
Male unknown.
Mann's description is sketchy, and there is apparently a confusing deletion of several lines coming near the middle of the last printed line on his p. 34. His artist's figure is also not very faithful in por- traying mandibular apices and head sculpture. Material examined: Only a few workers from the type series, collected by Mann in rotten wood (MCZ, USNM) . A~antho~nathus ocellatus
Acanthognathus ocellatus Mayr, 1887: 579, worker. Type loc.: Brasil, "St. Catharina."- Mann, 1916: 452, pi. 5, "fig. 38" (recte 39), queen, from Belim, Para, Brad.- M. R. Smith, 1944: 150, in key. Type worker currently in Museo Civico di Storia Naturale, Genoa, Italy, but pro- perly belongs in Naturhistorisches Museum, Vienna, Austria; not seen
by authors (discussed below).
Worker: If there is an "a,verage" or "typical" member of the genus, this is it. Head more convex dorsally than in A. rudis; posterior excision in full-face view evenly semicircular (rather than



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19691 Broutn and Kempf - Acanthognathus 9 7 V-shaped) ; ~osterior lobes very narrowly rounded. Mandibles slender and more than the head length (see Table I), with low we1ts or convexities developed on their inner margins beyond mid- length, but no ~rea~ical denticles. Compound eyes normally broad- elliptical, only weakly convex, with about 34-45 facets, greatest diameter 0.1 1-0.13 mm. One (Trinidad) specimen has the left eye abnormally small (diameter 0.08 mm) only about 9 facets)) whereas the opposite eye is nearly normal in size and facet number. The petiole is quite slender, especially as viewed from the side) and its node is a bit lower than in A. rudis; petiolar node widths of the available sample (n = 5 ) are 0.16-0.19 mm, modal at 0.17 ; while for A. mdis the width is 0.17-0.20 mm, modal at 0.18. The fossae of the sculpture are crowded on the anterior part of the cephalic dorsum, but are mostly well-separated on the posterior half of the head) with smooth or nearly smooth, shining interspaces. The fossae themselves have broad, shining bottoms. In the Trinidad worker, the posterior fossae are more often contiguous, and longitu- dinal rugulae begin to appear between some of them) making transi- tion toward the doubtfully distinct A. lentus. Sculpture of the truncus variable ; rugulose-punctulate, with interspersed small fossae ; sides of mesonotum usually smooth and shining, with scattered in- distinct fossae, as is sometimes also the anterior part of the propodea1 dorsum. Reticulo-punctulate sculpture of petiolar node confined to lowest parts of the sides (usually occupies most of side of node in A. mdis). Pilosity abundant on head and promesonotum, but not as abundant as in A. rudis. Color light to medium reddish-ferru- ginous, appendages lighter and more yeIlowish, gaster sometimes feebly infuscated,
Queen (dealate) from BelGm, Brasil. Greatest diameter of com- pound eye 0.19 mm ; petiolar and postpetiolar nodes relatively larger than in worker from same nest (petiolar node 0.20 mm wide). Pro- podeal teeth stout, but still long and acute. Mesonotum with crowded distinct fossae, contiguous and nearly so; interspaces and fossae smooth or nearly smooth, shining; scutum and scutel1um with median longitudinal carinula. Mesopleura smooth and shining, sides of pronotum rugose-fossulate, sides and dorsum of propodeurn in past finely rugulose-punctulate. Otherwise differing from the worker by the usual caste characters,
Male unknown.