Clypeasteroida

Characteristics

Clypeasteroids have several distinct characteristics that set them apart from other sea urchins. These include:

• Flattened, disc-shaped body: This shape allows them to burrow into sand and avoid predators.
• Five-pointed symmetry: Like other echinoderms, they exhibit radial symmetry.
• Petaloid ambulacra: These are five rows of tube feet that run along the body, resembling petals.
• Reduced spines: Their spines are short and blunt, unlike the long, sharp spines of other sea urchins.
• Mouth on the oral (lower) surface: They have a mouth positioned on the underside of their body.
• Anus on the aboral (upper) surface: The anus is positioned on the top of the body.

Environments

Clypeasteroids are found in a variety of marine environments, including:

• Sandy shores: They are commonly found in shallow, sandy areas along coastlines.
• Coral reefs: Some species live among corals.
• Deep-sea trenches: A few species have adapted to deep-sea environments.

Ecology

Clypeasteroids are important members of marine ecosystems. They play a role in:

• Sediment turnover: Their burrowing activities help to mix and aerate sediment.
• Nutrient cycling: They consume organic matter and release nutrients back into the environment.
• Habitat provision: Their burrows provide shelter for other organisms.

Fossil Record

Clypeasteroids have a rich fossil record dating back to the Eocene epoch, about 56 million years ago. Their fossils are often found in sedimentary rocks.

References

For more information on Clypeasteroida, consult these references:

• Hendler, G., Miller, J. E., Pawson, D. L., & Kier, P. M. (2015). Echinodermata. In *Zoology of the Northwest Atlantic* (Vol. 1, pp. 1-201). CRC Press.
• Mortensen, Th. (1940). A monograph of the echinoderms of the Danish West Indies. Copenhagen.