Clypeasteridae

Common Names

Members of the Clypeasteridae family are commonly called "sand dollars" due to their resemblance to the silver coins used in the past. Some species are also known as "sea cookies" or "pancake urchins" due to their flattened, disc-like appearance.

Characteristics

Clypeasteridae possess several distinctive features that differentiate them from other sea urchin groups:

• Flattened, Disc-Shaped Body: Sand dollars are flattened dorsoventrally, giving them their characteristic coin-like appearance.
• Radial Symmetry: Like other echinoderms, sand dollars exhibit five-fold radial symmetry. Their bodies are divided into five equal segments, each containing a row of tube feet.
• Reduced Spines: Unlike many other sea urchins, sand dollars have short, flattened spines that lie close to their bodies. These spines help with camouflage and movement in the sand.
• Five Ambulacral Grooves: On the oral surface (the underside of the body), they have five grooves called ambulacral grooves. These grooves are lined with tube feet used for locomotion and feeding.
• Lunariform Petals: On the aboral surface (the upper side), sand dollars have five prominent, lunariform (crescent-shaped) petals that radiate outwards. These petals are made up of ambulacral plates and house the tube feet.

Environments

Clypeasteridae are primarily found in shallow, sandy bottoms of tropical and subtropical marine environments. They often burrow into the sand to hide from predators and to access food sources. The distribution of different species within the family can be influenced by factors such as water temperature, salinity, and sediment characteristics.

References

For further information on Clypeasteridae, refer to the following online resources:

• World Register of Marine Species (WoRMS)
• PubMed