The Genitalia of the Mnesarchaeidae.

Transactions and Proceedings of the Royal Society of New Zealand, Volume 57, 1927, Page 710

The Genitalia of the Mnesarchaeidae. By Alfred Philpott, Hon. Research Student in Lepidoptera, Cawthron Institute, Nelson. [Read before the Nelson Philosophical Society, 2nd September, 1925; received by Editor, 10th September, 1925; issued separately, 19th February, 1927.] Plate 57. The Mnesarchaeidae are a small and highly specialized endemic family of the Lepidoptera Homoneura. At present the group consists of the type genus only, of which six species have been described. These are here tabulated in the order of the publication of their descriptions. Mnesarchaea paracosma Meyr., Trans. N.Z. Inst., vol. 18, p. 180 (1886). Mnesarchaea loxoscia Meyr., Trans. N.Z. Inst., vol. 20, p. 90 (1888). Mnesarchaea hamadelpha Meyr., Trans. N.Z. Inst., vol. 20, p. 91 (1888). Mnesarchaea fusca Philp., N.Z. Journ. of Sci. and Tech., vol. 5, p. 82 (1922). Mnesarchaea similis Philp., Trans. N.Z. Inst., vol. 55, p. 667 (1924). Mnesarchaea fallax Philp. This volume (1926). The group presents very striking differences in the male genitalia, characters, abundantly sufficient, indeed, to justify generic division in the opinion of those systematists who attach primary importance to these structures. But, though the six species fall into three very well-defined sections based on the characters of the male genitalia, I have not found that other structural characters satisfactorily support such divisions. For instance, hamadelpha, loxoscia, and similis have all the same type of genitalia and are obviously nearly related species, yet in venation the latter two are closer to paracosma, which has an altogether different type of genitalia, than to hamadelpha. Again, M. paracosma is nearer in genitalia characters to M. fusca than to M. fallax, but in venation M. paracosma and M. fallax are seen to resemble each other most nearly.

Description of the Male Genitalia.*In the present paper I have made some changes in the nomenclature of the parts formerly used by me, following in the main the system adopted by Eyer in the publication cited below. I here indicate these changes. Vinculum = the ninth sternite. Harpes = the clasping organs which articulate within the vinculum; formerly termed valvae. Sacculus = the lower lobe of the harpes; cucullus = the upper lobe of the harpes; frequently the harpes are not divided into these two parts. Aedeagus = the central organ which encloses the usually membranous penis. Penis = the continuation of the ductus ejaculatorius, ending in the eversible vesica. Owing to the marked differences between the species it is not practicable to give a general description of the genitalia characters. It may be noted, however, that the juxta is absent in all the species, and that the aedeagus consists only of the membranous ductus ejaculatorius. The species will now be considered separately. Mnesarchaea hamadelpha Meyr. Vinculum well developed, broadly U-shaped, upper angles rather produced. Harpes, sacculus triangular, armed within with a dense median patch of short hair and some more scattered hairs on the apical portion; cucullus as long as sacculus, finger-like, abruptly contracted into a fine point at apex, a few hairs along inner surface. The tegumen is represented by a pair of weakly chitinized flat lobes, the apical portions of which are rather hairy. These lobes curve towards each other apically and thus, in some measure, protect the anal tube. From the lower part of the lobes there is a curved extension inwards, which meets and fuses completely on the median line, forming a concave plate beneath the penis. Eyer has termed a somewhat similar organ in the Hepialidae a “suspensorium” and I adopt his name. The upper part of this structure is extremely strongly chitinized—a condition well shown in the photograph—and on the upper margin is a well-marked median incision. Behind this plate lie the anal and genital openings, the latter having two longitudinal spiny areas (cornuti) beneath it. The uncus is absent, as is also any chitinization representing the dorsal portion of the tegumen. Mnesarchaea similis Philp. Vinculum broad, quadrate, with produced upper angles. Harpes, sacculus triangular but curved scroll-wise in normal position, armature similar to that of hamadelpha, cucullus nearly as long as sacculus, finger-like, apex truncate and slightly expanded. Suspensorium somewhat heart-shaped, its apex widely and deeply emarginate, round the emargination the edge is irregular and more strongly chitinized. Beneath this stronger chitinization, in a median position, there is a rather large circular aperture. Mnesarchaea loxoscia Meyr. Vinculum intermediate between those of similis and hamadelpha. Harpes, sacculus bluntly triangular, smaller than in the two preceding species, cucullus slightly longer than sacculus, rather narrow at

base, thence slightly dilated, apex obtuse. Suspensorium subquadrate, broad basally, upper angles produced, a strongly chitinized band along upper margin, broadest at middle and narrowing rapidly to angles. Lobes of tegumen shorter and broaded than in the preceding species, apices broadly round-pointed. Mnesarchaea paracosma Meyr. The three species already dealt with illustrate varieties of a common type, but in paracosma we come to a widely different development of the organs. This species provides a very interesting example of asymmetry in genitalia structure, the two sides of the tegumen, the uncus, and the anal tube being the parts affected. Vinculum broad, but widely and deeply emarginate basally; from the median distal area two strong processes project beneath the harpes. Harpes, sacculus an irregular lobe with an armature of weak scattered hairs, cucullus finger-like, curved closely round apex of sacculus. From the base of the harpes, and membranously attached thereto, a narrow chitinous piece engages with the base of the suspensorium. This may be regarded, probably, as originally the lateral part of the vinculum which, owing to the throwing back of its attachment to the lower part of the tegumen, developed a convenient hinge at the most suitable point. Suspensorium enormously developed, projecting basally as a swollen lobed structure and distally as two long thin prongs which exceed in length the other parts of the genitalia. Tegumen consisting of left and right asymmetrical pieces, not fused dorsally. These pieces project in the general line of the body as thin stiff prongs. That on the left is fairly straight but the right prong is sharply angled outwards near its base, after which it resumes its original direction. This bend throws it quite clear of the rest of the genitalia, as is well shown in the dorsal and ventral views of the organs. Rising from where the lateral pieces of the tegumen approach each other dorsally, a thin curved prong, of about the same length as the prongs of the tegumen, bends over to the left. This I take to be a development of the dorsal portion of the tegumen and its curved apical part may be regarded as the uncus. The anal tube is attached to this apical part and is thus carried over to the left also, clear of its usual position in the median line. Mnesarchaea fusca Philp. Mnesarchaea fusca exhibits a type of genitalia structure quite different from that of any of the preceding species. The vinculum is shield-shaped. The harpes consist of a short, three-lobed outer piece and a low rounded basal extension inwards. From the base there proceeds a flat lateral piece which articulates loosely with the tegumen, thus taking on the function of the lateral arms of the vinculum. It will be seen, from the lateral view of the genitalia, that the vinculum, in this instance, could not without extreme modification carry out the function referred to. The tegumen has become a horizontal structure, its basal part deeply embedded in the abdomen and its apex divided into two strongly chitinized diverging prongs. These prongs apparently function as the uncus, but are probably

not homologous with that part in other Lepidoptera. Ventral of the tegumen is a membranous triangular plate supported by chitinized lateral rod-like pieces, which fuse basally with the ventral surface of the tegumen. This may be regarded as an outgrowth of the tegumen, a but slightly chitinized suspensorium. Between it and the uncus is the anal outlet, but there is here no extruded anal tube. Mnesarchaea fallax Philp. Vinculum large, lateral pieces broad and tapering to a blunt point. Harpes, sacculus short, broad, rounded; cucullus finger-like, stout, curved completely over apex of sacculus, apical half very strongly chitinized and bearing a number of short hairs. The tegumen appears to have taken up a horizontal position as in M. fusca. It forms a pair of lateral pieces to a weakly chitinized deeply bifid central structure, which appears to be a development of the closing membrane into a false gnathos. The anal tube lies immediately above this structure and there is no uncus or chitinized dorsal part. Only one specimen of this species was available for dissection, and the conclusions must therefore be regarded as tentative. The Female Genitalia. As the females of this genus are much more rarely taken than the males, I have only been able to secure material of two species for examination. These two, however, differ considerably, and require separate description. The abdomen consists of a very much reduced first segment, followed by six normal ones. In Mnesarchaea hama-delpha Meyr. the eighth sternite takes the form of a curved ventral plate, the basal part of which extends back into the seventh. The ductus bursae opens in the concavity of this piece. Above lies the eighth tergite, to which succeeds the not clearly separated ninth. Apically the ninth is slightly bifid and incurved. The ductus bursae is short and merges into the tube-like bursa copulatrix, which extends almost to the base of the abdomen, its apical third being minutely scobinate. In Mnesarchaea fusca Philp. the terminal tergite is much narrower than in Mnesarchaea hamadelpha; it is also more indented in the median line, forming two strongly chitinized hairy lobes. The eighth sternite is broad, apically somewhat indented and curved slightly downwards. The ductus bursae is a rather fine tube well defined from the globular bursa copulatrix. There is no trace of the segmental rods in either species, and from the appearance of the parts concerned in the deposition of the eggs it seems most probable that these are dropped indiscriminately, as in the Hepialidae. The study of the genitalia of the Mnesarchaeidae throws little light on the relationships of the family. Meyrick (Genera Insectorum, fascicule 132, p. 3), from a consideration of other characters, assigns the group to an intermediate position between the Micropterygidae, and the Plutellidae and Tineidae, though not on the direct line of descent. The genitalia characters, however, bear hardly any

resemblance to either of these three families. Eyer (Annals of the Entomological Society of America, vol. 17, p. 306) considers that the Mnesarchaeidae, as far as the genitalia are concerned, lie between the Hepialidae on the one hand and the Micropterygidae, Ericcraniidae, and Aculeate Tineoidea on the other. With the relationship to the Hepialidae (and consequently to the Prototheoridae) the present writer agrees, but can see very little approach to any of the other groups referred to. Nor does he accept Dr. Eyer's interpretation of some of the parts; the extreme specialization of the structures makes it a difficult matter to homologise them with more normal examples. For the photographic plate I desire to express my gratitude to Mr. Wm. C. Davies, of the Cawthron Institute, whose patience and skill are responsible for the excellent result.

Genitalia of Mnesarchaea species. (From mounts in glycerine jelly, ventral views, harpes folded out.) Fig. 22.—M. similis Philp. ♂ Fig. 23.—M. hamadelpha Meyr. ♂ Fig. 24.—M. loxoscia Meyr. ♂ Fig. 25.—M. paracosma Meyr. ♂ Fig. 26.—M. fusca Philp. ♂ Fig. 27.—M. fusca Philp. ♀

List of Figures. Fig. 1.—Mnesarchaea hamadelpha Meyr. ♀. Genitalia ventral view. Fig. 2.—M. hamadelpha Meyr. ♀ Abdomen, lateral view. Fig. 3.—M. fusca Philp. ♀. Genitalia, lateral view. Fig. 4.—M. similis Philp. ♂. Vinculum and harpes, ventral view. Fig. 5.—M. hamadelpha Meyr. ♂. Vinculum. Fig. 6.—M. hamadelpha Meyr. ♂. Vinculum and harpes, ventral view. Fig. 7.—M. similis Philp. ♂. Vinculum. Fig. 8.—M. paracosma Meyr. ♂. Genitalia, dorsal view. Fig. 9.—M. paracosma Meyr. ♂. Genitalia, ventral view. Fig. 10.—M. paracosma Meyr. ♂ Genitalia, right lateral view. Fig. 11.—M. fusca Philp. ♂ Vinculum. Fig. 12.—M. loxoscia Meyr. ♂ Vinculum. Fig. 13.—M. paracosma Meyr. ♂ Suspensorium, ventral view. Fig. 14.—M. paracosma Meyr. ♂ Right half of tegumen. Fig. 15.—M. paracosma Meyr. ♂. Left half of tegumen. Fig. 16.—M. fusca Philp. ♂. Harpes. Fig. 17.—M. fusca Philip. ♂. Genitalia, lateral view. Fig. 18.—M. paracosma Meyr. ♂. Harpe, from within. Fig. 19.—M. fallax Philp. ♂. Vinculum. Fig. 20.—M. fallax Philp. ♂. Tegumen and suspensorium, ventral view under coverslip. Fig. 21.—M. fallax Philp. ♂. Genitalia, lateral view. Lettering. a, anus. at, anal tube. be, bursa copulatrix. bs, basal part of suspensorium. cc, cucullus. db, ductus bursae. de, ductus ejaculatorius. dt, dorsal piece of tegumen. fbp, free basal piece of harpes. go, genital opening. h, harpe. 1pt, left prong of tegumen. It, lobes of tegumen. ps, prongs of suspensorium. rpt, right prong of tegumen. s, suspensorium. sc, sacculus. t, tegumen. u, uncus. v, vinculum. es, eighth sternite.