Sand dollars Facts

Sand dollars Facts
Sand dollars are marine invertebrates that belongs to the group of echinoderms. They are closely related to starfish, sea cucumbers and sea urchins. Sand dollars can be found in the temperate and tropical parts of Atlantic and Pacific Ocean. They live on the sandy sea floor, usually in the intertidal zone (near the beaches), or (rarely) away from the shore, on a depth of 30 feet. Pollution of the sea, habitat destruction and by-catch (they end up trapped in the shrimp trawls by accident) are the major threats for the survival of sand dollars in the wild. Despite these factors, sand dollars are numerous and widespread in the ocean.
Interesting Sand dollars Facts:
Sand dollars have round-shaped body that is usually 3 inches wide.
Sand dollars can be blue, purple, green, brown or black colored, depending on the species.
Sand dollars have flattened, rigid exoskeleton (called "test") with star-shaped mark on the surface. Their body is covered with numerous, small dark purple spines. Coin-like shells (of dead animals) are reason why they are known as sand dollars.
Skeleton can be light or heavy, depending on the habitat (heavy skeleton ensures survival in fast-flowing, turbulent waters). Young sand dollars swallow grains of sand to increase their weight.
Sand dollars move across the ocean floor using their miniature spines.
Mouth apparatus of sand dollars, better known as "Aristotle's lantern", consists of tiny teeth-like structures arranged in five sections designed for grinding of food particles. It is located on the bottom side of the body.
Sand dollars use spines and tiny appendages (cilia and tube feet) to collect food and guide it toward the mouth. They sometimes chew food 15 minutes before it becomes ready for swallowing and further digestion.
Sand dollars eat detritus, plankton, crustacean larvae, copepods, algae and diatoms.
Sand dollars use spines on the upper side of the body for breathing (like gills).
Sand dollars often gather in large groups. One square meter of sand can be covered with more than 625 sand dollars.
Natural enemies of sand dollars are predatory snails, sea stars and various fish (skates, starry flounders and wrasses).
Sand dollars will try to avoid predators by hiding in the sandy seafloor. They use spines to dig sand.
Sand dollars spawn during the spring (usually from May to July). Males and females release their reproductive cells directly into the water (external fertilization). Larvae swim freely and undergo several developmental stages. As soon as exoskeleton starts to form, sand dollars are ready to permanently settle on the sea floor.
Exoskeleton of sand dollars is made of plates of calcium carbonate. Number of growth rings on the plates indicates the age of sand dollar.
Sand dollars can survive 6 to 10 years in the wild.

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