Isoperla asiatica RAUŠER, 1968

Zwick, P & Surenkhorloo, P, 2005, The Mongolian Species Of Isoperlinae (Plecoptera: Perlodidae), Acta Zoologica Academiae Scientiarum Hungaricae 51 (3), pp. 253-276 : 264-266

Isoperla asiatica RAUŠER, 1968

( Fig. 7 )

Isoperla asiatica Raušer, 1968: 364 .

Material studied. Male holotype and female allotype, in alcohol, labelled “No. 113, Mongolia, KASZAB / Isoperla asiatica nov. sp. det Raušer 1966” ( HNHM) [Comments. According to the publication, the locality data are as follows: Mongolia, CA: Songino (3), Tula, stream, 13 July 1963. J. Raušer detached and cleared the penis membrane and returned it into the cavity of the 10th sternite after study; so did we. The allotype contains no mature eggs.] .

Additional material. MONGOLIA, Selenge aimak, Mandal sum: Khonin Nuga, Eroo River [49°05’N, 107°17’E], 2 ff , 24. VI.1998; 4 ff, 23. VI.2001; 4 ff, 14. VI.2002; 1 f, 17. VI.2002; 3 ff, 18. VI.2002; 11 f, 24. VI.2002; 20 mm, 19 ff, 16. VI.2003; 1 f, 17. VI.2003; 13 mm, 12 ff, 18. VI.2003; 3 mm, 3 ff, 19. VI.2003; 6 mm, 1 f, 21. VI.2003; 1 m, 1 f, 26. VI.2003; 4 ff, 29. VI.2003; 1 f, 1. VII.2003; 1 m, 3. VII.2003; 3 ff, 4. VIII .2003 ; Khonin Nuga, Khongi River , 2 ff, 18. VI.2003; 2 mm, 5 ff, 24. VI.2001; 1 f, 20. VI .2002 ; Eroo Hot Spring [49°05’N, 107°17’E], Ar-Ilchlekh River, tributary of Sharlan River , 1 m, 20. VI.2001; 2 ff, 28. VI .2003 ; Uram River, tributary of Khongi River , 7 mm, 4 ff, 25. VI.2003; 2 ff, 15. VII .2003 . KAZACHSTAN, surroundings of Ust Kamenogorsk [49°58’N, 82°36’E], River Malaya Ulbinka , 22.5.2003, leg. & det. V . DEVYATKOV, 16 mm, 32 ff (in coll. ZWICK).

The original description by RAUŠER (1968) illustrates details of penial armature, the mesosternal ridge, and ventral views of male and female abdominal tips. We describe and illustrate head and pronotum with their previously undesribed pigment pattern and various structural details, especially those of the penis and egg ( Fig. 7 ).

Colour pattern. General colour light ochre except brown pattern on head and pronotum; terga dorsally brown. Head pale yellowish with a brown mark over the ocelli extending towards the antennae and the occiput. There is a pale spot between the ocelli. Pronotum with the usual brownish muscle attachment marks between the pale centre and the pale lateral edges. Extent of pale pigmentation in centre apparently varies with age; in well-pigmented specimens, only a narrow pale band remains. Legs dorsally brownish, abdominal terga brown, Segments 9 and 10 yellowish.

Size. Fore wing length, mm 10.2–10.5 mm, ff 11.2–12.7 mm.

Structure. Typical of genus Isoperla . Legs long, femur about 5 times as long as wide, without setae, tibia with several sparse setae ventrally ( Fig. 7b ). The very dark cerci with fine ground pilosity and a fine crown of setae, a single ventral seta is very long and erect ( Figs 7d, e ).

Male. 8th sternum without the normal lobe-like appendage, middle of posterior margin only slightly thickened, in side view extending a little backwards towards sternite 9 ( Fig. 7c ). Sternite 9 forms the subgenital plate which is not distinctive. Everted penis upcurved, turned towards dorsum. Membraneous apical section inflated, with a back-curved little dorsal finger ( Fig. 7c ). The kneeshaped bend of the everted penis appears as an elongate swelling on the dissected penis membrane and is covered with fine transparent interconnected spicules which RAUŠER regarded as distinctive. The rest of the membrane is covered with many minute oval and slightly pointed teeth ( Fig. 7f ).

shown in full view and in profile, g = egg

Female. Subgenital plate broad and rounded, projecting little ( RAUŠER 1968, his fig. 81).

Egg ( Fig. 7g ). Regularly oval, 351 µm long, collar included. Collar almost straight, rim barely curved outward, surface without impressions. Base of collar barely projecting into egg. Anchor fungiform, with massive stalk. Chorion about 5.5–6.0 µm thick, uniformly covered with deep groove-like punctures.

Diagnostic characters and affinities. RAUŠER (1968) emphasized the comblike interconnected spicules of I. asiatica which are, however, seen only in transmitted light, at magnifications>200. Moreover, they are not unique, similar microtrichia occurring, for example, on the penis of I. difformis (KLAPÁLEK) ( BRINCK 1952) . Lack of a proper vesicle on male sternite 8, and the penis membrane without major spines or modifications remind one of I. potanini . However, I. potanini has an even less developed vesicle on sternite 8; for additional differences, see under that species. The female subgenital plate is not distinctive, but the regularly oval, strongly punctate egg with straight collar is characteristic. It is not clear which species may be the closest relative of I. asiatica .

Distribution. The type locality is in the Central aimak of Mongolia, not far from Ulaanbataar; our fresh material is from Selenge, to the northwest. However, the species was also found in Kazakhstan, its actual range remains to be explored.

Figures

Fig. 7. Isoperla asiatica RAUŠER. a = adult head and prothorax, b = hind leg, c = lateral view of male abdominal tip with everted penis; d, e, distal cercus segments with single large ventro-apical seta; f, cleared dissected penis with enlarged details of spicules, the frazzled spicules on the swelling being