Biologic evolution

The jackknife clam was put in the water tank in the house.
The action in jackknife clam's seawater
It saw while confirming it because it was being written in "Shellfish and
living thing of water" book in detail.
The jackknife clam enters sand walking.
The jackknife clam dives as having stood in sand.
Because the amount of sand in the water tank of the house is shorter than
the length of the jackknife clam (It is few), it is impossible that the
jackknife clam stands in sand.
The part of jackknife clam's water pipe and foot can be seen in the
photograph.

As for the jackknife clam, entering in sand was not, and was dead this morning.