北見山脈ウエンシリ岳附近の淡水産プラナリアの生態調査報告

抄録

In the present paper, the vertical distribution of freshwater planarians in the Mt. Wenshiri district, the Kitami Mountains in North Hokkaido, is reported. The highest peak, Mt. Wenshiri, is 1142 metres above sea level (Lat. 44°13′N. and Long. 142°53′E.). The main river systems of the area surveyed are the Okunayoro, the Okoppe, the Mookoppe and the Shokotsu. The Okunayoro River, the upper part of the Teshio River, discharges into the Sea of Japan ; the other three rivers empty into the Okhotsk Sea (fig. 1). The surveys were made in August 1962 and August 1963. In the district, the four species of freshwater planarians, Polycelis sapporo (IJIMA et KABURAKI), Polycelis akkeshi ICHIKAWA et KAWAKATSU, Polycelis schmidti (ZABUSOV) and Dendrocoelopsis lacteus ICHIKAWA et OKUGAWA, were found. Pol. sapporo, the commonest numerous-eyed white flatworm in Hokkaido in North Japan, was distributed in the localities below the altitude of about 420 metres. It was common in rivers, creeks, brooks and brooklets. Pol. schmidti was, however, common in the cold-water streams and springs within the altitude range from 300 to 560 metres. The animal is the common dark colored Polycelis species in North Hokkaido and is the most stenothermic among the Japanese freshwater planarians (cf. Kawakatsu 1964,1965). Pol. akkeshi, another numerous-eyed white flatworm in Hokkaido, was collected in some localities near Oshorokko (Okoppe River System). Den. lacteus was only found in two localities at Nishiokoppe and Kamiokoppe (alt. 100〜140 m). The inhabitable water temperature range of the above-mentioned four species found in the Mt. Wenshiri district is as follows ; Pol. sapporo (8.0〜16.0℃ ; including the data of Pol. akkeshi) ; Pol. schmidti (7.0〜14.0℃) ; Den. lacteus (7.6〜11.7℃). Pol. sapporo and Pol. schmidti were found together where their inhabitable water temperature overlapped. The habitats of planarians are also described in detail. No planarian was found in any localities of the Sakuru Waste Land, an argillaceous zone along the upper part of the Shokotsu River (fig. 1,table 1). The type of vertical distribution of the district is S-SC-C (S : Pol. sapporo ; C : Pol. schmidti). The result of the present investigation shows that the planarian fauna and the type of vertical distribution in the Kitami Mountains differ from that of the Mt. Daisetsu district in Middle Hokkaido(cf. YAMADA 1962 ; YAMADA & TANJI 1962,1964).