＜正＞A sand dollar is a type of sea urchin（海胆）.Many are flat,but others are more rounded.These rounded ones are called sea biscuits.Sand dollars are often found together on the ocean floor or seabed.They eat small sea creatures,algae（海藻）,and the remains of animals that reach the ocean floor.Sand dollars have spines,and thus,very few creatures are interested in them-too hard to bite!In the ocean,sand dollars can be different colors including brown,green,blue,and purple.People usually see them when they are washed up on the
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