Sand Dollars move on the sand with the help of their spines. It drives them against the sand. However, in water, the sand dollar utilizes its five petal-shaped pores to take water in the internal vascular system and move. It doesn’t use tube feet for locomotion.
In short, the spines and the pores make them mobile. Moreover, the movement of sand dollars differs from that of sea urchins.
Yearning to know more about the unique movements of these tiny echinoderms? Then, without any further ado, jump to the next section!
Sand Dollars cannot be categorized as sessile organisms like plants.
Instead, they belong to the mobile category of echinoderms.
They have two different locomotory organs to move on the sand and in water:
- Flower shaped pores
- Spines and Cilia
The Sand Dollars test is covered with hundreds of thousands of small, soft spines that grant it a velvety feel.
These spines are one of its locomotory organs.
They act as tiny spades that help sand dollars to move via coordinated movement in one direction.
This not only lets them move across the sea bed and coastal area. But it also allows them to dig and nestle into the sand.
The spines certainly can’t help sand dollars move in deep water and oceans.
So, it uses the internal water vascular system for locomotion in that situation.
The five pores are present on the upper surface of the exoskeleton of this minute creature.
It takes in water to the vascular system. Then it moves under the principles of hydrodynamics.
That is why sand dollars are known as hydrodynamically attuned organisms.
A common quizzing about Sand Dollars is how they settle at the bottom of the ocean and stand against the strong water currents and waves.
So, sand dollars have special adaptions for it.
They “weigh belt” themselves to become heavy and thus stand the strong waves.
Sand dollars sift small particles of magnetite and sand into them.
This helps them an anchor to the sand at the bottom of the sea floor.
Moreover, key sand dollars have a special adaptation to stand against harsh water currents. They have holes called lunules.
These holes help them remain burrowed in the sand and thus prevent them from lifting out due to any strong water current.
Not all the spines are for locomotory purposes. Some spines and cilia aid the tube feet in capturing food.
These numerous spines capture the phytoplankton and ferry them along the test until it reaches the Central mouth opening on the lower side of the body.
The movement of sand dollars is quite different from that of sea urchins.
We just brought to light that sand dollars use their spins and vascular system for motility.
However, in contrast, a sea urchin uses its long tube feet to crawl and move in addition to its spines.
Moreover, they have a ball and socket joint that helps attain coordinated spin and tube movements.
Although sand dollars also have tube feet, they aren’t for locomotion and movement.
Instead, it is used in filter feeding and capturing prey.
Unfortunately, an upside-down sand dollar can’t become straight by itself.
They dig themselves deep into the sand and then wait for water currents to flip them into the right position again.
So, if you see an inverted sand dollar on the sand, please put it slowly into the water back.
If you touch a live sand dollar, it moves as a result.
The reason is that they have sensory receptors on their test and spines.
So, every time you touch a sand dollar, it will move a wee bit.
However, be careful while touching one. They have numerous small, tiny spines that can puncture your skin.
If a sand dollar isn’t moving, there is a high chance that it is dead.
So, look for its spines and color. If you find
- The tiny echinoderm to be bleached out.
- Spines and cilia shed off.
It means that the sand dollar is no longer alive.
Sand Dollars have sensory organs and receptors that help them sense touch. They often move their tiny spines and tube feet in action.
Sand Dollars use two organs for locomotion:
- Spines and cilia present on the calcium carbonate test
- Five flower-shaped pores that allow movement through water distribution
Some sand dollars have special slot-shaped longitudinal holes in them called lunules.
These sand dollars are called keyhole sand dollars.
These holes help them burrow deep in the sand and prevent high-current waves from lifting them up.
Sand Dollar spends most of its life in the sea’s low and mid-tidal regions.
The reason is that it can easily breathe there using the oxygen of water.
Moreover, it finds multiple preys there to feed on.
Generally, sand dollars have a lifespan of 6 to 10 years.
After which, they start to shed their spins and die. Only a few manage to live up to 13 years.
The average size of the sand dollar ranges between 2 to 4 inches in diameter.
However, a sand dollar as large as 6.5 inches has been found.
Speaking of the point, sand dollars are mobile organisms.
They use their spines and five petal-shaped pores for locomotion.
The former helps to move on the sand, while the latter helps to attain mobility in water.
However, it doesn’t use tube feet for locomotion. Instead, they serve as feeding organs.