Scyphodon

A mysterious genus that has been described from and is only known from the male caste of Scyphodon anomalum. The only known material was collected in Wai Lima, Lampongs, Sumatra and these males are so unusual that this taxon was not initially placed in the Formicidae. Brues (1925) had this to say in the introduction to the description: The strange Hymenopteron described below was included among some insects collected in southern Sumatra by H. Karny and H. C. Siebers. Although I have been unable to determine its systematic relationships with any degree of satisfaction, the insect presents such striking characters that it will be very easily recognizable by anyone who may have opportunity to study its habits or to discover the other sex.

Identification
Petersen (1968) - Scyphodon should no doubt be retained as a separate genus within the Leptanillinae, characterized mainly by three apomorphic features: 1) the large paddle-shaped mandibles, 2) the long apparently fourth segment of the abdomen, which I consider to represent the fused segments 4 and 5 of the abdomen, and 3) the unique genital structure. The mandibles and the genitalia are quite unique among the Hymenoptera.

Nomenclature

 *  SCYPHODON [Leptanillinae]
 * Scyphodon Brues, 1925: 93. Type-species: Scyphodon anomalum, by original designation.
 * Scyphodon in Leptanillinae: Petersen, 1968: 591; Baroni Urbani, 1977c: 482; Dlussky & Fedoseeva, 1988: 79; Bolton, 1990b: 277; Hölldobler & Wilson, 1990: 12; Bolton, 1994: 70.
 * Scyphodon incertae sedis in Formicidae: Wheeler, G.C. & Wheeler, J. 1985: 259.
 * Scyphodon excluded from Formicidae, incertae sedis in Aculeata: Ogata, Terayama & Masuko, 1995: 33.
 * Scyphodon in Leptanillinae: Boudinot, 2015: 32.

Petersen (1968) - This peculiar hymenopteron was described by Charles T. Brues in 1925 on the basis of two specimens from Sumatra.

As Brues himself said, he was unable to determine the systematic position of the species with any degree of satisfaction, and the well-known hymenopterologists Rohwer and Fagan, whom he consulted, were also unable to solve the question; all three could not even definitely determine the sex of the specimen. As far as can be judged from the short and somewhat unconvincing discussion in his paper, Brues thought that his striking species would find its place in the Bethyloidea or Proctotrupoidea or perhaps in a family of its own. (Surprisingly enough, Brues at first found a position near Braconidae reasonable).

The systematic position of Scyphodon has apparently not been discussed since the original description, though Brues himself probably indulged in some reflections on the question when, as editor of “Psyche,” he processed the paper by G. C. & E. W. Wheeler (1930) on the leptanilline ant species Phaulomyrma javana. Although there are some striking differences between the mandibles and terminalia of Scyphodon and Phaulomyrma it is clear that they are related in such a way that Brues could have transferred his species to the Formicidae, with the male-based species then placed in the subfamily Leptanillinae. This transfer is hereby formally made, on the basis of the description and figures by Brues, and a redescription may be presented later if the types are found; (they are not in the Museum of Comparative Zoology, Cambridge, according to Dr. Howard E. Evans, and Dr. David R. Smith has been unable to find them in the U.S. National Museum, Washington; Dr. M. A. Lieftinck, Leiden, informs me that the collectors very likely gave the specimens to Brues).

Scyphodon should no doubt be retained as a separate genus within the Leptanillinae, characterized mainly by three apomorphic features: 1) the large paddle-shaped mandibles, 2) the long apparently fourth segment of the abdomen, which I consider to represent the fused segments 4 and 5 of the abdomen, and 3) the unique genital structure. The mandibles and the genitalia are quite unique among the Hymenoptera.

It is impossible to interpret the genital structure with confidence from the description and figures of Brues (reproduced in figs. 15A, C, D). According to him the genitalia proper constitute the tubular piece with the large oval aperture anterior to the acutely pointed tip. This tube is supported by, and fused to, the long sternum 9. Such a fusion of the genitalia and the hypopygium would be most unusual and it seems unlikely that it has actually taken place. I hazard the guess that the terminal structure of Scyphodon is somewhat like that of Noonilla as described above, and therefore the dorsal tube is interpreted as the aedeagus, with a dorsal, oval, phallotreme as in Noonilla. The ventral supporting sclerite is interpreted as a modification of the proximal shaft of the genital organ, which in Noonilla is composed of the strongly reduced gonocoxites and the volsellar plates, and the pair of longitudinal thickenings near the apex (fig. 15C) may be homologous with volsellar digiti. Sternum 9 is apparently strongly reduced, as is tergite 9 (+10). However, as long as the actual specimens cannot be studied this interpretation of these peculiar genitalia is mere guess-work.

The wing structure and venation of Scyphodon are closest to Noonilla (fig. 6), but in other general characters the species is more similar to the Leptanilla-Phaulomyrma complex, due especially to the horizontal head and laterally compressed thorax.

It is quite understandable that Brues did not consider Scyphodon anomalum to be an ant. This species is less ant-like than e.g. Leptanilla palauensis (Smith, 1925), and Dr. Robert W. Taylor (i. l.) informs me from his experience working with palauensis in 1964, that “though Drs. Evans, Burks and Krombein all felt that Smith's palauensis was definitely an ant; Brown, Wilson and myself, as ant specialists were, at least initially, somewhat dubious.” Dr. Taylor now considers that placement of these species, and the others discussed here, in the subfamily Leptanillinae is acceptable, but emphasises the need for collection of such males in association with workers or queens before the assignment are conclusively proved.

Male
Trochanters one-jointed. Abdomen consisting of six segments in addition to an apical stylus, subpetiolate, the first segment campanulate, separated from the second by a slight but distinct constriction, third segment the longest, hypopygium greatly prolonged. Antennae 13-jointed, filiform; scape moderately lengthened. Prothorax extending to the tegulae, short above. All coxae contiguous, tibial spurs 1, 2, 2. Anterior wing with a subcostal cell, long marginal vein, an incompletely closed radial cell, and one indistinctly defined basal cell; otherwise veinless. Mandibles broadly paddle-shaped, not dentate.

Head nearly twice as broad as the thorax, much constricted behind, the temples broadly rounded. Eyes small, rounded, highly convex, densely hairy. Mandibles large oval, paddle- or spoon-shaped, convex and concave internally, fringed with hair and hairy on the convex surface, with a tooth-like projection above at the base. Oral aperture large; maxillae apparently consisti'1g each of a finger-shaped stalk bearing a minute 1-jointed palpus. Antennae as long as the head and thorax, inserted at the anterior end of the long horizontal front; scape twice as long as any of the flagellar joints which are longer than the pedicel. Ocelli well developed, in a minute triangle close to the occiput. Thorax long and narrow, pronotum visible from above, but very short medially; mesonotum twice as broad as long, gradually broader behind; scutellum separated by a transverse .groove at the base, longer than wide, obtusely pointed behind. Propodeum small, rather evenly sloping and without separated upper and posterior faces; its surface smooth, without carinae; spiracle small, circular. Propleurae very long, extending backwards almost to the regulae. Mesopleurae and mesosternum very large, mesothorax swollen below so that the mesopleura is below the level of the tip of the front coxae. Abdomen, exclusive of the hypopygium, as long as the remainder of the body, consisting of six segments, the first two short, of about equal length, third more than twice as long; fourth and fifth shorter, but still longer than the second; sixth as long as the third but much narrower and obtusely pointed at the tip. Hypopygial structure arising beneath the base of the sixth segment, as long as the entire thorax or the five basal abdominal segments; seen from above (Fig. 1, D) it contains a median tubular piece with a large oval aperture just before the tip which is acutely pointed, to the sides of the median piece the sternite is visible. In lateral view the upper part of the dorsal median piece appears above the sternite to which it is seen to be, fused; from below (Fig. 1, C) the whole structure appears as a long tube with a pair of longitudinal thickenings near the apex. Legs slender, the anterior femora somewhat thickened; tarsal claws simple. Wings large; submarginal vein twice as long as the marginal; radial vein straight, except at extreme base, as long as the marginal.