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Monday, April 11, 2016

Brittle Stars

Photo Credit: Fish and Karate
Brittle stars are echinoderms. They crawl across the sea floor using their flexible arms for locomotion. Brittle stars generally have five long, slender, whip-like arms which may reach up to 24 inches in length on the largest specimens. They are also known as serpent stars; the New Latin class name Ophiuroidea is derived from the Ancient Greek ὄφις, meaning "serpent".

Many of the brittle stars are rarely encountered in the relatively shallow depths normally visited by humans, but they are a diverse group. Over 2,000 species of brittle stars live today. More than 1200 of these species are found in deep waters, greater than 200 m deep.

The mouth is rimmed with five jaws, and serves as an anus (egestion), as well as a mouth (ingestion). Behind the jaws is a short esophagus and a large, blind stomach cavity which occupies much of the dorsal half of the disk. Brittle stars have neither a head nor an anus. Digestion occurs within 10 pouches or infolds of the stomach, which are essentially ceca, but unlike in sea stars, almost never extend into the arms.The stomach wall contains glandular hepatic cells.

Brittle stars can readily regenerate lost arms or arm segments unless all arms are lost. Ophiuroids use this ability to escape predators, in a way similar to lizards which deliberately shed (autotomy) the distal part of their tails to confuse pursuers. Moreover, the Amphiuridae can regenerate gut and gonad fragments lost along with the arms. Discarded arms have not been shown to have the ability to regenerate.

Did you know?
  • Brittle stars live in areas from the low-tide level downwards. 
  • Brittle stars use their arms for locomotion. They do not, like sea stars, depend on tube feet, which are mere sensory tentacles without suction. 
  • Brittle stars can live up to 5 years.

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