在牠们身体顶部和底部的中央，是钮扣状的吸盘。
In the middle of their bodies on both the top and bottom, are button-shaped disks.
它们身体中间上下长有钮扣状的吸盘，用来吸进或排出海水。
In the middle of their bodies on both the top and bottom, are button-shaped disks. Through these disks they draw in or expel sea water.
它们身体中间上下长有钮扣状的吸盘，用来吸进或排出海水。
In the middle of their bodies on both the top and bottom, are button-shaped disks. Through these disks they draw in or expel sea water.
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