By Bob Goemans
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Polyp Lab 

Sand Dollars

 Clypeaster reticulatus (Reticulated Sea Biscuit)

Clypeaster reticulatus
(Linnaeus, 1758)

Reticulated Sea Biscuit

Likely Reef Tank Suitable

Likely Fish-Only Tank Suitable


Sand dollars are in the Order Clypeasteroida and are basically nothing more than flattened sea urchins and sometimes referred as 'irregular' urchins. Their spines are extremely short, i.e., about 2 mm long and since they are so close together they feel smooth to the touch. Small tube feet are also found among the spines.

Feeding habits are generally determined by its position in the sand. When moving through sand, it feeds on detritus and diatoms by sweeping the food through its food grooves into the mouth by using cilia. It also can take a somewhat vertically position with only part of its body embedded in the substrate. In this position it becomes a suspension feeder using its spines and tube feet.

Most are found in protected sandy flat areas. If a low tide leaves the sand dollar somewhat exposed, they will be found lying flat on the sand and still, i.e., without movement. When they are under the still waters of a sheltered bay, they also lie flat on the bottom but move around a lot. In areas where there is even slight water movement, sand dollars can stand vertically with a third or more of their test/exoskeleton buried in the sand. Their inclination to the substrate and their orientation to the current varies with the strength of the current. In areas of very rough water, sand dollars again lie flat and generally prefer to be mostly buried.

Family Astriclypeidae

Family Clypeasteridae

Family Clypeasteridae

Family Dendrasteridae

Family Mellitidae

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