How
a Horseshoe Crab Moves
A horseshoe crab usually crawls on the bottom of the sea, but it
can also crawl on land. It has four pairs of walking (and feeding) legs
and one pair of longer walking legs in the back that push it forward, like
it's skiiing.
photo
permission: Hiroaki Sugita
Horseshoe
crabs can also swim, but they mostly swim at night when sea gulls and other
birds won't attack them. To move from walking to swimming, a horseshoe
crab does much like an airplane does when it is taking off. It slowly starts
running. It uses its legs to push its body up as high as possible, and
it beats its gill plates to help it move. Then the front of the shell slants
upward,
and the crab
does a backward somersault in slow motion. It keeps moving in a slanted
direction until it finally reaches the surface of the water. There it levels
off and starts to swim. It may seem strange, but a horseshoe crab swims
on it back! After swimming for several minutes, the horseshoe crab needs
to rest. It slowly starts to sink back down to the bottom. If it decides
it doesn't want to go to the bottom, it will start moving its feet and
gill plates and start swimming up to the surface again. If it falls all
the way to the bottom, it will use its tail and turn itself over.
photo permission: Hiroaki Sugita
The shape of the horseshoe crab's shell helps it both when it is swimming
and when it is walking. When it is swimming, the crab is like a boat with
a round bottom, and it can move through the water easily. When it is crawling
on sand, the shape of the shell keeps the waves from turning it over
so easily.
Horseshoe crabs can also bury in the sandy and muddy bottoms.
photo
permission: Assateague Naturalist
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