Echinoderms

General

• Greek “Echinos” meaning “spiny” and “dermos” meaning “skin"
• Approximately 7,000 species
• Includes starfish, sea urchins, sand dollars, sea cucumbers, sea lillies

 Distribution

• Exclusively marine animals, no freshwater

Habitat

• Benthic animals
• Found usually on the sea floor in every marine habitat from the intertidal zone to ocean depths

 Body

• They are triploblastic.
• Larval form show bilateral symmetry and adult forms show radial symmetry
• Body is unsegmented without a head
• The body is uniquely shaped. It can be star like, elongated or spherical

 Reproduction

• Sexes are separate, Echinoderms are either male or female
• Become sexually mature after about two to three years
• Most release their eggs and sperm into the water where they are fertilized externally
• A female can release one hundred million eggs at once

Divided into:

 Subphylum:  Asterozoa

•      Class  Asteroidea            Sea Stars & starfishes 
•      Class  Ophiuroidea         Brittle Stars

 Subphylum:  Crinozoa

•      Class  Crinoidea              Sea Lilies & Feather Stars

 Subphylum:  Echinozoa

•      Class  Echinoidea           Sea Urchins and Sand Dollar
•      Class  Holothuroidea     Sea Cucumbers