Schizorchis yamashitai sp. n. (Cestoda: Anoplocephalidae) from the Northern Pika Ochotona hyperborea Pallas in Hokkaido

Abstract

Schizorchis yamashitai sp. n., from the northern pika in Hokkaido, is described and its morphological characteristics compared with those of the three previously known species of Schizorchis Hansen, 1948. The zoogeography of Schizorchis spp. in pikas is briefly discussed. Three species of cestodes, all from pikas, Ochotona spp. (Lagomorpha:Ochotonidae) are recognized in the genus Schizorchis Hansen, 1948. S. ochotonae Hansen, 1948, and S. caballeroi Rausch, 1960 are known from North America; while S. altaica Gvozdev, 1951, occurs in eastern Eurasia. Since the cestodes of this genus are highly host specific, additional species might be expected in other Palearctic regions where the helminth fauna of pikas has not been investigated. The geographically isolated populations of the northern pika Ochotona hyperborea Pallas on the islands of Hokkaido and Sakhalin are especially interesting from this standpoint. While collecting mammals in northern Japan during July to August 1962, I secured five specimens of O. hyperborea yesoensis Kishida in central Hokkaido. This paper describes a new species of Schizorchis found in three of these animals. The cestode is named in honor of Professor Jiro Yamashita, Head of the Department of Parasitology, Faculty of Veterinary Medicine, Hokkaido University, who provided laboratory space and invaluable assistance in connection with the field work in Japan. The material consisted of eight cestodes, of which six possessed gravid segments. One specimen, stained with 2% methyl-greenpyronin, was partially dissected; the others were stained with Semichon's acetic carmine or Ehrlich's acid hematoxylin and mounted in toto. Received for publication 1 October 1962. Schizorchis yamashitai sp. n. (Figs. 1 to 3) (All measurements in millimeters.) Diagnosis: Strobila 100 to 185 long, with as many as 338 segments; maximum width, 3.5 to 3.75, attained in gravid segments. Strobila widens abruptly just posterior to scolex, gradually increasing in width through about one-fifth of its length; thereafter, strobilar width essentially uniform. All segments wider than long; mature segments with length/width ratio of about 1:6; gravid segments, about 1:3. Gravid segments somewhat arched in dorsoventral view. Margins of strobila slightly serrate, with serrations more strongly defined toward posterior end of strobila. Scolex small and weakly developed, from 0.236 to 0.250 in width; suckers about 0.085 in diameter. Unsegmented neck very short or lacking. Accessory longitudinal excretory canals numerous. Genital pores irregularly alternate, situated in posterior half of segmental margin. Genital primordia appear very early; that of ovary visible within 1 mm of scolex, and those of male genital organs within 10 mm. Genital ducts dorsal to longitudinal excretory canals. Cirrus sac elongate, 0.286 to 0.428 long by 0.042 to 0.064 in maximum width (average 0.344 by 0.052) in mature segments; diameter greatest near distal end. Cirrus sac infrequently extending anteromediad as far as lateral margin of poral ventral excretory canal. Everted cirrus protruding about 0.130, with diameter of about 0.025; spines present. Internal seminal vesicle ovoid and small, situated in proximal portion of cirrus sac; external seminal vesicle much coiled, extending mediad from cirrus sac to level of ovary. Testes subspherical, averaging 0.050 in diameter in mature segments, and numbering 34 to 53 per segment (average 44). Testes distributed across segment near posterior margin and not separated into two discrete lateral groups; usually confluent posterior and dorsal to vitelline gland as best seen in postmature segments. Testes never extending laterally 479 This content downloaded from 157.55.39.104 on Mon, 20 Jun 2016 06:38:34 UTC All use subject to http://about.jstor.org/terms 480 THE JOURNAL OF PARASITOLOGY Vol. 49, No. 3