The Yufuin hot-spring is located at the foot of Mt. Yufu (450-500m above the sea) in Oita Prefecture. In the vicinity of this spring, there are many hot-springs, namely, Takemoto, Yunotsuho, Tanakaichi, Hachiyama and Ishimatsu, all of which belong to the simple carbonate springs. I found the following animals in both Takemoto and Yunotsubo on May 13th and 14th, 1937:
Takemoto I: 37.5°C, pH 7.25……………Stenothyra sp.
Takemoto II: 34.5°C, pH 7.2……………Aplocheilus latipes (Temminck & Schlegel), Phoxinus steindachneri Sauvage.
Takemoto III: 30-35.2°C, pH. 7.25…Caridina denticulate de Haan, Sernisudcospira libertina Gould.
Takemoto IV: 45.8°C, pH 7.4……………Laccobius sp.
Yunotsubo I: 40.2°C, pH 7.7……………Gerris lacustris (Linné)
Yunotsuho II: 32.37°C, pH 8.5-8.75…Rana, japonica Günther, (tadpole), Aplocheilus latipes, Stratiomyia. japonica Van der Wulp (larva), Gerris lacustris, Lycosa pseudoannulata (Roesenberg & Strand), Lymnaea japonica Jay and Stenothyra sp.
Rana, Laccobius, Stratiornyia and Lymnaea are commonly found in hot-springs, while Caridina and Stenothyra occur rarely. During the present study too Caridina are found in the limited thermal pools. It is very peculiar that many kinds of animals are found in alkaline springs at 1 unotsubo, as in the case reported by Brues (1932) that the insects usually occur in alkaline thermal waters, the pH-values of which range from 8.0 to 8.5.
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