Isoperla altaica ŠÁMAL, 1939

Zwick, P & Surenkhorloo, P, 2005, The Mongolian Species Of Isoperlinae (Plecoptera: Perlodidae), Acta Zoologica Academiae Scientiarum Hungaricae 51 (3), pp. 253-276 : 259-262

Isoperla altaica ŠÁMAL, 1939

( Figs 3 , 4 , 5 b-d, 6a)

Isoperla altaica Šámal : 421, figs 4, 5.

Isoperla altaica - ZAPEKINA DULKEIT, 1955. 169, figs 5–9.

Material studied. MONGOLIA: Chovd aimak, ca 35 km N Somon Uenč, Mongol Altaj Gebirge , 1750m, kl. Nebenbach des Uenč gol, 8.VII.1966, 1 mm [KASZAB 646]. Selenge aimak, Mandal sum, Khonin nuga: Bar-Chuluut River [48°58’638N, 106°57’013E], tributary of Eroo River , 1 f, 07.IX.1999; 3 ff, 21.VIII.2001; 2 mm, 4 ff, 04.VIII.2003 (all leg. P. SURENKHORLOO). KAZACHSTAN, surroundings of Ust Kamenogorsk [49°58’N, 82°36’E], basin of River Gornaya Ulbinka , 11.6.2000, leg. & det. V. DEVYATKOV, 8 mm, 9 ff (in coll. ZWICK). RUSSIA, Kurile Islands , Iturup Island , 1 m, 1 f, 1.8.1998, Lake Iturup , River Blagodatnaya , leg. & det. V. TESLENKO .

The male type specimen was collected on the River Karas, outflow of Lake Kara-Koli , by the staff of the Hydrobiological State Institute in Leningrad and was given to J. ŠÁMAL for study. The type is not in the collection of the Zoological Institute St. Petersburg today ( ZHILTZOVA 1995) and may be lost. ŠÁMAL emphasized its slight brachyptery. His illustration shows a large ventral lobe on sternite 8. Tergite 10 was described and illustrated as “partly open” medially. However, this condition was probably an artifact, perhaps through drying because there is really only a weakly sclerotized median strip .

The original description of body pattern is not detailed. We accept the interpretation of the first revising author ( ZAPEKINA-DULKEIT, 1955; 1975) who distinguished I. altaica from a new species, I. eximia ; see also there. The central dark mark on the head is entire and extends to the front edge of the pronotum. In front of it, the head is pale to its front border. A less dark band-like transverse mark extends from the centre of head to the compound eyes. The median part of the meso- and methathoracic scuta is darker than the lateral portion ( Fig. 3a ).

Size. Fore wing length, mm 8.2–8.8 mm, ff 10.5 mm (specimens from Khonin nuga); mm 8.0– 8.2 mm, ff 10.3–11.2 mm (specimens from Kazakhstan).

Male. Specimens from Kazakhstan are slightly brachypterous, i.e., the wings extend barely beyond the abdominal tip while those from Khonin Nuga ( Mongolia, upper reaches of Eroo River) have normal wings. Abdomen dark brown both dorsally and ventrally, except the large ventral lobe on sternite 8 which is strikingly pale yellow, especially the rounded distal edge. Tergite 10, nal segments 6–9, ventral view paraprocts and general shape of subgenital plate normal ( Figs 3b, c ). Pilosity of dark brown cerci resembling those of I. asiatica ; see there. Penis membraneous, armed with a large asymmetrical sclerite ( Figs 3e, f ) which stands on the rear face of the everted organ, its slender, slightly twisted apical section points downward ( Fig. 3g ). Minute scales ( Fig. 3f ) cover most of the surrounding membrane.

The appearance of the asymmetrical penis sclerite differs depending on slight differences in the positioning of specimens. In side view, the basal part of the sclerite is broad, more than 3 times wider than the apical part. However, when viewed from the apex of the sclerite one notices that only that side of the sclerite is enlarged which lies on top when the curved apex points to the right hand side. The upper edge of this side forms a blunt crest, the opposite side is low and rounded ( Figs 3d, e , 6a ).

Female ( Fig. 3h ). Subgenital plate short, projecting only a little, distal margin shallowly indented in the middle, shiny, dark, finely pilose, like the rest of the segment.

Egg. Plump, regular oval with blunt poles. There is a prominent egg shoulder because a raised ring surrounds the plateau from which the collar rises ( Fig. 4 ). The collar lacks distinct meshes but has a finely crenulate margin. The base of the fungiform anchor in the deeply embedded center of the collar is straight and flat. Micropyles not observed.

Eggs from Khonin Nuga measure 360×250 µm and have a thin, structureless chorion of uniform width (7–8 µm). In contrast, eggs from near Ust Kamenogorsk are smaller (295×235 µm), their chorion is finely punctured, in optical section a fine radial striation extends across the chorion which is almost 13 µm thick near the equator of the egg, but only about 9 µm near the opercular pole or next to the ring around the collar.

Larva ( Fig. 5b ). We illustrate a pharate male in its larval skin which had the penis sclerite already developed. It differs from the larva previously assigned to I. altaica ( ZAPEKINA-DULKEIT, 1955) ; see under I. lunigera .

Notes and affinities. The penial sclerites of all specimens are similar. However, there are differences in wing length, egg size and egg chorion thickness between populations. Future studies based on more material are desirable.

I. lunigera , I. altaica and I. eximia belong to the I. sordida species-group distinguished by a large unpaired penis sclerite freely projecting from the membrane. At this time, the present three are the only known Palaearctic members of the group which includes a number of species in western North America ( SZCZYTKO & STEWART 1979). The asymmetry of the sclerite suggests that I. altaica and I. eximia are close allies.

Figures

Fig. 3. Isoperla altaica Šámal. a = head and prothorax, b, c = male abdominal tip in ventral and dorsal views, respectively; d, e = penis sclerite in lateral and caudal views, respectively, f = spicules on penial membrane next to large sclerite, g = male with everted penis, lateral view, h = female abdomi-

Fig. 4. Isoperla altaica ŠÁMAL, egg and details of collar; specimen from Khonin Nuga

Fig. 5. Larvae of Isoperla spp. a =I.lunigera (KLAPÁLEK), b–d = I.altaica ŠÁMAL, with details of labium and labial segment

Fig. 6. Isoperla altaica ŠÁMAL (a) and I. eximia ZAPEKINA-DULKEIT (b, c). Penis sclerites (a, b; to same scale) and fore body (c; not to scale)