著者

森 主一

出版者

東京動物學會

雑誌

動物学雑誌

巻号頁・発行日

vol.50, no.1, pp.1-12, 1938

被引用文献数

4

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1. Donax semignosus DUNKER (Fig. 1), a mussel living at the sandy beach of the sea, manifests a characteristic tidal rhythmic migration. The observation of this rhythmic migration and the experimental analysis of the behaviour at the flood tide were performed at the coast of Okinosu in Tokusima-Si (Fig. 2), during late August and early September in 1937. 2. This animal lives beneath the sand of the beach washed by the waves (Fig. 11 and 12), and at the flood tide it makes shoreward migration inn accord with the rising of the surface of the sea, and at the ebb tide offshore retreat with the lowering of the sea level. The animal thus shows up-and-down movements synchronus with those of the tides. The distance of the migration was 3-6m at the neap tide, but at the spring tide it was often over 30m (Table 1, Figs. 3 and 4). 3. The method of the migration is characteristic. At the flood tide, the mussels lurked beneath the sand suddenly jump out to the surface of the sand just in front of the top of the surf (this motion requires 0.5-1.5 sec.) to be carried shoreward by it and then quickly insure the supporting point by inserting the foot into the sand so as not to be carried back again by the retreating current, nad in the next moment they disappear beneath the sand with quickly repeating motions of the foot (this movement requires 3-6 sec.). By repeating these movements the animals can perform the migration towards the higher parts of the beach (Figs. 5 and 6). On the contrary, at the ebb tide, they suddenly jump out to the surface when the lapped wave just begins to retreat to find themselves in the next moment at the lower parts of the shore, and then burrowing into the sand, disappear from the surface. By repeating these movements the mussels can accomplish the migration towards the lower parts of the shore (Fig. 6). 4. By several experiments and observations, it was proved that the jumping-out behaviout in front of the top of the surf at the flood tide was due to the shock or the vibration of the sand given by the wave when it beats the shore (Figs. 7-10). 5. This migrating behaviour seems to be concerned with food habit of the mussel. It feeds on minute living organisms at the beach and it is convenient for the animal to remain throughout the day at the beach where sand grains and consequently many minute organisms attached to them are always stirred by lapping waves. 6. The wedge-shaped triangular shell and the arrow-headed foot are all well adapted to execute the migration which needs the quick motion of the animal (Fig. 13). Accessory notes: 7. A king of the crab, Remipes truncatifrons MIERS (Fig. 14), which lives abundantly at the same beach mentioned above, shows up-and-down movements synchronous with those of the tides. The quick motion of this animal remembers that of the said mussel.