They
are wonderful
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A mussel digging into the sand
- With small light movements of the foot, the mussel makes a hole in
the sand. Powerful movements would cause it to fly away because it is
so light in the water.
- When the mussel has dug itself down a bit into the sand, it relaxes
its adductor muscle and the two shell halves go apart so the surrounding
sand is compressed and packed harder. The mussel is then well anchored
for when it digs deeper with its foot. Excavation is made easier when
water is squirted out of the shell casing around the foot.
- By pumping blood down to the foot it is able
to function as an anchor. When the mussel constricts its foot, the lateral
muscles pull the rest of the body downwards. This is made easier by
small shell movements that cause trixotropi around them.
Try sticking different objects in the sand - in different ways - and in
different types of bottoms. Try observing how different animals dig down
into the sediment.
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Figure
3
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