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Flora and Fauna
Pennatulacea
SUMMARY
Pennatulids or seapens are colonial cnidarians which have an stiff internal calcite rod - the rachis. They have two types of polyps: large feeding polyps (autozooids) armed with eight tentacles and smaller openings (syphonozooids) which regulate and maintain water currents within the body of the sea-pen. Zooids can be arranged individually over the body or as linear groups on 'leaves'.
Pennatulids stand erect anchored in the sediment by a long base section of the rachis buried in the sediment. Sea-pens are suspension feeders, the zooids capture plankton with their tentacles.