Report on the ecological survey of freshwater planarians in the Syakotan Peninsula and Niseko mountainous districts

Abstract

In this paper, the vertical distribution of freshwater planarians in the Syakotan Peninsula and Niseko mountainous districts in South Hokkaidô(Lat. 42°45'N. to Lat. 43°25'N. and Long. 140°20'E. to 141°00'E.) is reported. The Syakotan Peninsula is the lower mountainous land (the highest peak, Mt. Yobetsu-dake, is 1, 298 metres above sea level) and runs out to the Sea of Japan. The Niseko mountainous district is situated at the south of the Syakotan Peninsula. The district is characterized by volcanoes belonging to the Nasu Volcanic Zone, such as Mt. Nisekoan'nupuri (altitude, 1, 309 metres), Mt. Iwao'nupuri (1, 554 metres), Mt. Chise'nupuri (1, 135 metres) and Mt. Nito'nupuri (1, 082 metres). There are several hot springs at the foot of mountains. The main river systems of the area surveyed are the Yoichi, the Horikabu and the Shiribetsu. The surveys were made in July 30 to August 1, 1966.
In the area surveyed, four species of freshwater planarians, Dugesia japonica ICHIKAWA et KAWAKATSU, Polycelis sapporo (IJIMA et KABURAKI), Polycelis auriculata IJIMA et KABURAKI and Dendrocoelopsis lacteus ICHKAWA et OKUGAWA, were found. D. japonica and Den. lacteus were collected only in the stations in the seashore of the Syakotan Peninsula. Pol. Sapporo was common in the stations both in the seashore and the mountainous districts. The altitude of the upper limit of distribution of this species is about 730 metres (inhabitable water temperature range, 7.9-17.2°C). Pol. auriculata was rather common in the stations in the Niseko mountainous district within the altitude range from 220 to 730 metres (7.9-13.0°C). The type of the vertical distribution in the area surveyed is shown as JS-SA-A (J:D. japonica; S:Pol. sapporo; A:Pol. auriculata).