The Echinoids consist of the sea urchins and sand dollars, with bodies shaped like globes or discs. Characteristically they have a hard shell and spines. Many are herbivores, feeding on algae, but others are predators. Sea urchins move by their podia or tubular feet and also their movable spines and many burrow. Sand dollars also burrow into soft sediments and may bury themselves completely, digging with their movable spines.

Related categories 1

ADW: Class Echinoidea
Photographs and information on the heart urchins, sand dollars and sea urchins from the Animal Diversity Web.
Calcareous Flowers: Tests and Cross-sections of Sea Urchin Spines.
Photographic study by Richard Howey with some fine photographs of the intricate beauty of these structures.
Echinoid Directory
Biology, phylogeny, and classification of sea urchins.
The Echinoids
Information about sea urchins, such as how they live, feed, and reproduce. There is also an alphabetic listing of their taxa. From The Natural History Museum, London.
Edible Sea Urchin: Echinus esculentus
Photographs and information from ARKive including classification, status, description, range, habitat, biology, threats and conservation.
Loxechinus albus
Factsheet from the FAO on the Chilean Sea Urchin which is eaten in Chile and Peru, its distinguishing features, distribution, habitat and biology.
Purple Sea Urchin: Strongylocentrotus purpuratus
Photographs and information from ARKive including classification, status, description, range, habitat, biology, threats and conservation.
Red Sea Urchin
Information from Wikipedia on this species, Strongylocentrotus franciscanus, including its description, feeding habits, behavior and reproduction.
Sea Urchin Embryo
A page from the Laboratory of Embryonic Gene Expression, included here for three beautiful photographs.
Sea Urchin Embryology
Laboratory modules using sea urchin eggs to explore fertilization and development.
Sea Urchin: A Stinging but Amazing Animal
Article by Jean-Marie Cavanihac on these animals with many photographs of their development.
Sea Urchins Revisited
Photographic study by Jean-Marie Cavanihac of the sea urchin with some microscopic features of interest to the amateur naturalist.
Strongylocentrotus purpuratus
Photograph and information on the purple sea urchin.
Who is in Charge Here?
Illustrated article by Richard L. Howey considering how creatures with no brains, such as the sea urchin, react appropriately to their surroundings.
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