179. 貝蝦分布の氣候條件と其の形態特性との關係

抄録

With the exception of 4 species of Caenestheria and 2 of Cyzicus occurring between the isotherms of N 10°C and 20°C in July and a species of Caenestheria farther north beyond the isotherm of 10°C, all of the living estherids are distributed between the Northern and Southern isotherms of 20°C in July and January respectively, but the number of species tends to decrease in regions that are warmer than 30°C in July. Furthermore, the fact that many species are crowded in the basins along the Donau, Nile and other rivers cannot be overlooked. It may therefore be concluded that a temperate climate (+20°C in Summer) in the continental basin is the optimum for the estherids. Among the seven genera of estherids, Caenestheria, Caenestheriella and Leptestheria are eurythermal and Eoleptestheria and Cyzicus stenothermal, the remainder being intermediate.
When the four species of Caenestheria known from the Tundra region are morphically compared with 4 species of stenothermal Cyzicus and 4 species of Eohrtestheria, also stenothermal, living in the Hungarian besin, the climate of which is quite suitable for estherids, it is found that the estherids in such unsuitable climatic condition as in the Tundra are commonly diminutive in form, with smaller number of growth lines. The ornamentation between the growth lines is independent of climatic conditions but of value in attempting classification of this group as demonstrated in the joint paper by the senior author and HIIZITA.
From these observations, it can easily be presumed that glaciation of the past in Central Asia must have offered a barrier to their distribution. In this connection it is noteworthy that 8 of the 14 species known in Eastern Asia belong to eurypic genera while stenopic genera are represented by only 2 species.
Of Mesozoic Estherites in Koreo-Manchuria it is known that the large ones are most common in the Jehol fauna, the reverse being true in the case of the Daido fauna. In the Kyöngsang and Sungari faunas the size is mostly medium, growth lines being however, commonly more numerous in the Kyöngsang forms. This fact together with others on the palaeogeography and palaeoclimatology suggests that the climatic conditions were the optimum for Estherites in the Jehol period while it was most unfavourable in the Daido period.