B-1 



OCTOCORALLIA 

 (=Alcyonaria) 



Octocorals are colonial anthozoan coelenterates. They differ 

 from other coelenterates in that their polyps have an octamerous 

 biradial symmetry, and (with a few exceptions) their coenenchymal 

 tissue contains minute calcareous structural elements called 

 spicules. Unless secondarily modified, the polyps typically have 

 eight pinnately branched tentacles, eight complete septa with septal 

 filaments, and one siphonoglyph. Such polyps are termed autozooids. 

 In some species there is also a second type of polyp called a 

 siphonozooid. Siphonozooids are smaller than autozooids, they have 

 only a single pair of septal filaments, and their tentacles are 

 greatly reduced in size or absent. Species with both polyp forms 

 are said to be dimorphic. 



Octocoral polyps vary in appearance depending on their state 

 of contraction or retraction. When alive the polyps are often 

 observed with the body and tentacles fully expanded; however, the 

 tentacles can also be contracted and curled in over the mouth of 

 the polyp while the body of the zooid remains extended (permanently 

 so in some species). Furthermore, in some species the entire 

 upper portion of each polyp (anthocodia) is retractible into the 

 lower portion (anthostele) . The anthosteles are often raised up 

 on cylindrical, or conical wart-like prominences called calyces, 

 which are distinguishable on the surface of the colony even when 

 the polyps are completely retracted. The calyces are usually 



