Class Echinoidea (sand dollars, sea urchins, heart urchins, cake urchins)

1. Radially symmetrical.
2. Skeleton well suited for fossil preservation and is strongly developed.
3. All are benthic.
4. Most species retain the anus at the aboral pole and have a circular circumference.
5. Fertilization is external and development is via an echinopluteus larva in most species.
6. Feed by selective or indiscriminate grazing and scavenging or by gross sediment ingestion.
7. Growth is related to temperature and very dependent on diet.

Echinoidea is a class that belongs to the phylum Echinodermata. Species that belong to this class are the sand dollars, cake urchins, sea urchins, and heart urchins. Echinoids have an egg shaped, circular body which is hemispherical. They have skeletal plates that bear many movable spines and three jawed pedicellariae. Echninoids also have tubed feet, however they do not have arms. Located just inside of the mouth of echinoids is Aristotle's Lantern which is used for feeding and movement. Echinoids are marine animals that are common on sea bottoms.

• Echinoid skeletons are well suited for fossil preservation.
• The relative abundance of echinoid fossils gives the taxon a complete fossil history.
• A few species including most antarctic species have yolky eggs withdirect development. Most antarctic and subantarctic species brood their young,some in marsupial indents on the females.
• The maximum age of echinoids is about 10 years. Predators of echinoids are seagulls, fish, sea otters, asteriods, gastropods, crustaceans, and ofcourse humans.

1. Banister, Dr. Keith and Dr. Andrew Campbell. 1985. The Encyclopedia of Aquatic Life. New York: Facts on File.
2. Bertin, Leon. 1967. Larousse Encyclopedia of Animal Life. New York: The Hamlyn Publishing Group Limited.