Clypeaster

Clypeaster is a genus of sea urchins in the family Clypeasteridae, commonly known as “sand dollars.” These echinoderms are characterized by their flattened, disk-shaped bodies, resembling a coin or a dollar, and are often found in shallow marine environments. Clypeaster species are widely distributed across the world’s oceans, particularly in tropical and subtropical regions.

Clypeaster Australasiae – Clypeaster australasiae

Common Names

While the name "sand dollar" is the most widely recognized, Clypeaster species are also referred to as "sea cookies" or "pancake urchins." These descriptive names highlight the flat, coin-like appearance of these animals.

Characteristics

Clypeaster sea urchins possess several unique characteristics:

  • Flattened Body: The most prominent feature is their flattened, disk-shaped body, which allows them to burrow into sand and sediment.
  • Five-Point Symmetry: Like other sea urchins, Clypeaster exhibits five-point radial symmetry, with a distinct central point surrounded by five radiating lines.
  • Ambulacral Grooves: The upper surface of the test (the shell) displays five ambulacral grooves that run from the central point towards the edges. These grooves contain tube feet that aid in locomotion and feeding.
  • Petaloid Areas: The ambulacral grooves are often widened and bordered by petaloid areas, giving the test a distinct floral appearance.
  • Anus on the Dorsal Side: The anus is located on the dorsal (upper) side of the test, typically towards the center.
  • Mouth on the Ventral Side: The mouth is positioned on the ventral (bottom) side, equipped with five jaws and teeth for scraping algae and organic matter from the substrate.

Environments

Clypeaster species are typically found in shallow, sandy or muddy environments along coastlines. They prefer areas with moderate wave action and relatively stable sediments. These sea urchins can be found in both intertidal and subtidal zones, with some species inhabiting depths of up to 100 meters.

References

For more information on Clypeaster, refer to these reliable sources: