Report on the ecological survey of freshwater planarians in Sapporo City and its adjacent district

Abstract

In this paper, the vertical distribution of freshwater planarians in Sapporo City and its adjacent district in Central Hokkaidô is reported. Sapporo City is situated at the northern part of the Ishikari lowland area. Its adjacent district is the lower mountainous land (the highest peak, Mt. Yoichi-dake, is 1488 metres above sea level). The main river system in the area surveyed is the Toyohira River (the large tributary of the Ishikari River which enters into the Ishikari Bay, the Sea of Japan). Surveys of the stations in Sapporo City were made during the years 1956-1965. Surveys of the majority of the other stations were made in July and August, 1965.
In the area surveyed, seven species of freshwater planarians, Dugesia japonica IGHIKAWA et KAWAKATSU, Phagocata vivida (IJIMA et KABURAKI), Phagocata iwamai ICHIKAWA et KAWAKATSU, Polycelis Sapporo (IJIMA et KABURAKI), Polycelis auriculata IJIMA et KABURAKI, Dendrocoelopsis lacteus ICHIKAWA et OKUCAWA and Dendrocoelopsis ezensis ICHIKAWA et OKUGAWA, were found. Ph. iwamai, Den. lacteus and Den. ezensis were found only in the biotopes in the Ishikari lowland area. D.japonica was found in the biotopes below the altitude of about 285 metres. Ph. vivida, one of the common planarian species in South and Central Hokkaidô, was found only in the brooks, brooklets and springs in the Ashiribetsu River (one of the tributary of the Toyohira River). Pol. sapporo was most common in the biotopes both in the plain and the mountainous district. Pol. auriculata was rather common in the biotopes within the altitude range from about 160 to 1019 metres.
The inhabitable water temperature ranges of the above-mentioned species of freshwater planarians which were found in Sapporo City and its adjacent district are follows : D.japonica (2.0-19.8°C); Ph.vivida (7.8-10.8°C); Ph.iwamai (2.0-19.6°C) ; Pol. sapporo (2.0-23.5°C); Pol auriculata (4.5-15.7°C); Den. locteus(2.0-19.6°C) ; Den. ezensis (2.0-19.6°C).
The type of the vertical distribution in the area surveyed is shown as JSV-SVA (Ashiribetsu River) or JS-SA (the other district). The typical type of the vertical distribution in South and Central Hokkaido is shown as JSV-SVA-VA-A (cf. KAWAKATSU 1965, Table I). It seems that the types JSV-SVA and JS-SA are the part of the original type.