Sometimes you find this strange shell on the seashore, rather dirty, and
not always sweet-smelling. You might also find Sea-urchins half-dead,
washed into the rock-pools. The shells are wonderful objects, so you
should clean them in fresh water; they are well worth the trouble of
taking home.
All over the shell you will see little rounded knobs. These show where
the spines were fixed on; each spine fits into a hole in the shell, but
so loosely that it is able to move about. The Sea-urchin can walk by
moving its spines, tilting its body along from one place to another on
the bed of the sea. It can do much more than that. Like its cousin the
Starfish, it has numerous tube-feet, so you would not be surprised to
see this prickly ball walk up the face of a rock.
The tube-feet, or sucker-feet, are fixed to the shell in much the same
way as the spines. They can be bent this way or that. If the Urchin is
on a rock he clings tightly with these sucker-feet; then, if he wishes
to move away, you will see the long thin tubes stretch out and bend
about. They fix themselves to the rock, and the animal is drawn along.
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