Dr. Murai Éva - Gubányi András szerk.: Parasitologia Hungarica 29-30. (Budapest, 1997)

with a mean of 0.290 mm; the mean length of blade and handle is 0.164 mm (0.132-0.190) and 0.129 (0.112-0.159), respectively. The measurements of small hooks are as follow: mean length 0.189 mm (0.155-0.212); mean blade and handle lengths 0.101 mm (0.0900.111) and 0.097 mm (0.069-0.127), respectively. Morphologically, the larvae were characterised by long hooks with relatively long blade and short base. Most of the adult stage parasitic worms found in pikas are strictly host specific (cf. Gvozdev 1962, Hobbs 1980). However, those parasitic as larval stages have been recorded as common to rodents. A review of the literature indicates that pikas harbour T mustelae (cf. Gubanov 1964, Saveliev 1972), T. polyacantha (cf. Fedorov and Potapkina 1975), 7! krepkogorskii (1c. Babaev and Sapargeldyev 1970), some unknown species of Taenia with strobilocercus and Cysticercus type larvae (cf. Barrett and Worley 1970) found in North America, Taenia=Hydatigera sp. Gvozdev, 1962 (lc. Yun-Lyan 1963; cf. Gvozdev 1962, Sulimov etal. 1974, Sulimov and Obukhov 1974, Gvozdev and Orlov 1985) found in Asia, Echinococccus multilocularis (cf. Tokobaev and Erkulov 1966, Sulimov et al. 1974, Sulimov and Obukhov 1974, Gvozdev and Orlov 1985), and T. hydatigena (cf. Fedorov and Potapkina 1975). This last one is common in ruminants, and perhaps represents accidental infection in the pika. Only Taenia sp. larvae Gvozdev, 1962 are believed to be specific for pika. Of these cestodes, T. polyacantha, T. krepkogorskii and Taenia sp. Gvozdev, 1962 possess pseudostrobila-like larvae. Unfortunately, the morphology of North American specimens of strobilocercus and Cysticercus type larvae, found in O. princeps, has not been described (see Barrett and Worley 1970). The present larvae can be distinguished from those of other species by their characteristic shape and hook morphology and their dimensions (Table 1). A comparison of larvae collected from pikas of Mongolia and Kazakhstan showed that their hooks differ in length and shape. The Taenia sp. larvae Gvozdev, 1962 showed greater resemblance to the larvae of T. mart is. Kornyushin and Sharpilo(l 986) synonymised them with T martis. Pseudostrobila-like larvae with an armed scolex may be divided into three groups, namely armatetrathyridium (T. polyacantha, T. martis), strobilocercus (T. taeniaeformis)

, and polycephalic metacestodes that are known Fig. 2. The crown of rostellar hooks of Taenia rétracta. Scale bar: 0.3 mm. Fig. 3. Large and small hooks of Taenia rétracta. Scale bar: 0.2 mm. DISCUSSION