Abstract
The vertical distribution of the freshwater planarians in the Teshio Mountains (the Uryu mountainous district) and its adjacent seaboard district on the Sea of Japan in central and North Hokkaido is reported. The Teshio Mountains are rather low mountains and the highest peak, Mt. Pissiri, is 1031.5 metres above sea level. The seaboard district on the Sea of Japan consists of two topographical units, one is the low land (the district between Wakkanai and Rumoi) and the other is the Mashike mountainous district (the main peak, Mt. Shokanbetsudake, is 1491 m high). The area surveyed is situated in Lat. 43°30′N. to 45°30′N. and Long. 141°20′E. to 142°30′E. The main river systems of the districts are the Ishikari, the Teshio and several short rivers (the Enbetsu, the Kotanbetsu, the Obirashibe and the Shokanbetsu). Surveys were made chiefly in the summers of 1962,1963,1964 and 1965. In the area surveyed, nine species of freshwater planarians, Dugesia japonica ICHIKAWA et KAWAKATSU, Phagocata vivida (IJIMA et KABURAKI), Phagocata iwamai ICHIKAWA et KAWAKATSU, Phagocata albata ICHIKAWA et KAWAKATSU, Polycelis sapporo (IJIMA et KABURAKI), Polycelis schmidti (ZABUSOV), Dendrocoelopsis lacteus ICHIDAWA et OKUGAWA, Dendrocoelopsis ezensis ICHIKAWA et OKUGAWA and Dendrocoelopsis sp. of Otoineppu, were found (including the data of Dr. KAWAKATSU). Pol. sapporo was found everywhere in the streams and springs both in the seashore district and the stations below the altitude of about 460 metres. Pol. schmidti was rather common in the cold-water localities in the Teshio Mountains and at Teshio-cho (alt. 15-740 m). Ph. vivida was collected only in the cold-water spring at On'nenai (the northernmost locality of this species). The other six species were found chiefly in the localities in the plain. The inhabitable water temperature range of the main species of freshwater planarians is as follows : Pol. sapporo (6.2-18.3℃) ; Pol. schmidti (7.0-10.2℃). The type of vertical distribution in the area surveyed is JSC-SC-C. The geographical distribution of Ph. vivida, Pol. auriculata and Pol. schmidti in Hokkaido is also described (modification of the deduction of the Dr. KAWAKATSU's 1965 article). 1. The northern limit of distribution of Ph. vivida : the Oshima Peninsula〜Sapporo〜Mt. Teshio〜the Shiretoko Peninsula. 2. The northern limit of distribution of Polycelis auriculata : the Oshima Peninsula〜Sapporo〜Mt. Teshio〜Kushiro. 3. The southern limit of distribution of Pol. schmidti : Mt. Pisshiri〜Mt. Teshio〜Akan〜the Shiretoko Peninsula.
