GENERAL ZOOLOGY 



Sclerosepta 



Skeleton 



Fig. 10.15. An individual stony coral, showing the relationship between the animal and its 

 calcareous skeleton. (Adapted from K. von Frisch, 1953, Biolooie, vol. 2, by permission of 

 Bayerischer Schulbuch-Verlag.) 



Other representative anthozoans are the true corals, such as Astrangia danae, 

 a northern coral (Fig. 10.14), and the many species abounding in tropical 

 seas. The coral individual resembles a small sea anemone lying in a limy, 

 cup-like skeleton secreted by its epidermal cells. The stony mass of a coral 

 head or reef, covered completely by the living substance of its polyps, is 

 contributed to by the secretory activites of large numbers of these individuals, 

 producing skeletal material beneath them and forming new polyps by bud- 

 ding or subdivision as the size of the mass increases. The living individuals 

 are found only at the surface (Fig. 10.15); the underlying stony material is 

 uninhabited, except as it may be invaded by a variety of worms, crustaceans, 

 bivalves, and other animals of the reef. The part played by corals (Fig. 

 10.16) in the formation of coral islands and of the limestone in various 

 deposits has given these coelenterates an important role in geologic history. 



Other anthozoan types are numerous, such as the sea pens, sea fans, and 

 many others (Fig. 10.16). All are marine, and many produce skeletons to a 

 considerable degree, of either organic or inorganic materials. Anthozoans 

 have in common the fact that no free-swimming medusoid stage is found in 

 their life cycles. In se.xual reproduction gametes are produced by the sessile 

 polyps, and a new generation develops from the resultant planulae. 



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