Leptanilla exigua

Distribution based on Regional Taxon Lists
Palaearctic Region: Tunisia.

Nomenclature

 *  exigua. Leptanilla exigua Santschi, 1908: 519, figs. 1, 3 (m.) TUNISIA.

Taxonomic Notes
Petersen (1968) - I have been able to study the surviving specimens of the male-based Leptanilla species described by Santchi (1907, 1908). These belong to Naturhistorisches Museum, Basel and consist of a single type-labelled specimen and two additional specimens of each of the four species, e. g. Leptanilla tenuis, Leptanilla minuscula, and Leptanilla tanit described in 1907, and Leptanilla exigua described in 1908. All of these specimens were labelled by Santchi but not all of them belong to the true type material. Thus the two additional specimens, labelled as L. tenuis, are not from the type locality, Kairouan, and they do not seem to be that species but rather they represent respectively L. tanit (locality: Hammaref, Tunesie) and an apparently new species (locality: Le Kef, Tunesie, Dr. Normand). Also one of the Santchi labelled specimens of tanit is probably wrongly identified and seems close to the apparently new species just mentioned from Le Kef.

Unfortunately, except for the two additional specimens of tenuis mentioned above, all specimens are mounted in balsam between cover-glasses and thus difficult to examine due to ackward positions and sometimes severe shrinking. A revision and redescription of the Santchi species, therefore, must await the capture of fresh material. However, since Santchi's papers contain several errors and his figures are especially unreliable, it is in order to make some remarks, first of all on two features of generic interest, the wing venation and the terminalia.

Petersen 1968

Wing venation. In the fore wing Santchi recognized the presence of a vein only in one of his species, namely L. tanit, but his figure of it is far from correct (fig. 2a in his 1907 paper, not fig. 3a which shows minuscula, the figure texts are transposed). It shows a straight vein which in all its length runs obliquely to the costal margin of the wing. In fact the venation, although very much reduced, is more complicated as can be seen from fig. 14. The main vein complex consists of 1) a narrow but very distinct subcosta, 2) a very long marginalis, 3) a straight radialis, and 4) a short, upper basal vein; in addition a weakly indicated analis is present. A true pterostigma is lacking; it is obvious transformed into the long marginal vein. The proximal part of the marginalis and the basal vein have a brownish pigmentation of a conspicuous, cracked appearance. Subcosta bears a few long setae.

This type of venation is also found in the other Santchi species, although in a still more reduced form. Only in L. minuscula a complete wing could be studied. It lacks the radialis and the basal vein, but the subcosta and the long marginalis, with the characteristic pigmentation, are both present. Apparently L. tenuis and L. exigua have the same venation but I have only been able to study the proximal part of the fore wing in these species. Apart from a clearly shorter radialis, the above-mentined Leptanilla specimen from Le Kef has a venation similar to that of L. tanit.

The reduced venation in species like L. minuscula represents one of the extremities of a morphological cline within the Leptanillinae. The other extremity of the cline is the relatively rich venation of Noonilla copiosa (fig. 6), whereas the conditions in species like Scyphodon anomalum (fig. 15), Phaulomyrma javana (fig. 16), and L. tanit (fig. 14) are connecting links in the chain.

Terminalia. Santchi was especially unlucky when he figured the abdomen of his species. It is not very serious that his figures show, erroneously, that L. tenuis (1907, fig. 1) and L. minuscula (1907, fig. 3) have a long and slender abdomen, but it is a bad error and very confusing to have turned the genitalia upside down obviously in all four species. In reality the distal flattened part of the aedeagus is dorsal in all species, and not ventral as shown by Santchi in all figures of his paper from 1907. In other features of the genitalia his drawings arc by no means perfect, but on the other hand, not too bad, as they show roughly what can be seen in the preparations of the specimens. However the bad standard of preservation allowed only the larger parts of the genitalia to be drawn with some confidence, whereas the more delicate structures, such as the volsellae, could not be reliably reproduced. Fortunately an unmounted specimen from Santchi's collection could be dissected and studied in some detail and a better understanding of the general build of the terminalia could be obtained. The specimen studied is the above-mentioned one from Le Kef.

The abdominal segment 9 is shown in fig. 13. The sternum is a small rhomboidal or triangular plate with a bifurcated posterior tip. It is in firm connection with the much larger, posteriorly very weakly sclerotized tergum, the lateral portions of which bend over on to the venter and fuse for a short distance. As in L. astilina n. sp. described above, segment 9 is thus a socket into which the genital capsule is fitted. Pygostyli are lacking. A row of setae on tergum 9 may indicate the line where tergum 10 could be fused to tergum 9.

The genital capsule is shown in figs. 11 and 12. A gonobase is totally lacking. The gonocoxites are large valve-like structures with free margins all the way round; they are widely separated dorsally, but ventrally they meet each other. The gonostyli are apically bifurcated and turned inward under the aedeagus. The inner side of the gonocoxites below the gonostyli is moderately convex and setaceous. The volsellar plates are not fully recognizable as they are very delicate; they are probably inflected dorsally into the lumen of the proximal part of the aedeagus from the ventral margins of the gonocoxites. A pair of large, rod-like lobes are the volsellar digiti; they are provided with rather long setae on the free distal portion. Volsellar cuspital lobes are not recognizable. The aedeagus is broad and its proximal part is thick and sub-cylindrical whereas the distal part is flattened and covers the volsellar digiti and the inflected gonostyli like a shield. The tip of the aedeagus is divided as shown in the figures.

As far as they could be studied the terminalia of the four Santchi species are built in the same way as described above in the Leptanilla specimen from Le Kef, but the elements of the terminalia vary in shape from species to species and are of taxonomic value. This appears already from Santchi's papers and I can mainly confirm what he says about the form of the aedeagus and the tips of the gonostyli in the different species, for example, but his descriptions of the volsellae and his figures of these structures are not reliable, as already mentioned above. Unfortunately the study of Santchi's material does not give much new information on these structures. The volsellar digiti of L. exigua are build almost as in the specimen from Le Kef; the lobes are somewhat longer, richly setaceous and relatively well sclerotized. In the remaining species the digiti are apparently much smaller. This is definitely so in L. minuscula as already can be seen from the figure by Santchi (1907, fig. 3c).

The Leptanilla species from Tunesia, Africa, obviously make up a rather uniform group which can be differentiated from other leptanilline taxa on the basis of the structure of the genitalia. Surprisingly enough the investigations on the material from the collection of Santchi have shown me that all four Santchi species are good species, and a fifth species (from Le Kef) may be added.

These five species are distinguishable by features of the genitalia, but also characters of the head capsule, the antennae and the petiole provide good landmarks for the recognition of the species.

L. tenuis and L. tanit both have a short head (about one third longer than wide) in combination with long flagellar joints (about twice as long as wide), whereas L. minuscula, L. exigua and the Leptanilla species from Le Kef have a long head (at least more than 1.75 times longer than wide) and short, quadrate flagellar joints. L. tanit is readily distinguished from the other species by the shape of the node of the petiole; in profile the node in this species is very strongly convex anterodorsally rather than evenly slanting as in the other species, in dorsal view the anterior margin of the node looks slightly bilobate due to the advanced lateral parts, faintly recalling the condition in the queen of L. theryi Forel as described by Santchi (1915, p. 57, fig. 3).

References based on Global Ant Biodiversity Informatics

 * Baroni Urbani C. 1977. Katalog der Typen von Formicidae (Hymenoptera) der Sammlung des Naturhistorischen Museums Basel (2. Teil). Mitt. Entomol. Ges. Basel (n.s.) 27: 61-102.
 * Baroni Urbani C. 1977. Materiali per una revisione della sottofamiglia Leptanillinae Emery (Hymenoptera: Formicidae). Entomologica Basiliensia 2: 427-488.
 * Santschi, F. 1908. Nouvelles fourmis de l'Afrique du Nord (Égypte, Canaries, Tunisie). Annales de la Société Entomologique de France 77: 517-534.
 * Scupola A., and R. Ballarin. 2009. The genus Leptanilla Emery, 1870 in Sicily (Hymenoptera: Formicidae). Myrmecologische Nachrichten 12: 129-132.
 * Yasumatsu K. 1960. The occurrence of the subfamily Leptanillinae in Japan (Hymenoptera, Formicidae). Esakia 1:17-20.
 * Zolessi, L.C. de and Y.P. de Abenante. 1973. Nidification y mesoetologia de Acromyrmex en el Uruguay III. Acromyrmex (A.) hispidus Santschi 1925 (Hymenoptera: Formicidae) Revista de Biologia del Uruguay 1(2):151-165