CTENOPHORA 31 



The Octocorcd'la, or those forms which have eight tentacles, are found 

 in all seas, both in shallow water and at great depths. They include 

 the organ-pipe coral, the precious red coral (Corallium rubrum) of the Medi- 

 terranean Sea, and the sea-pens and the sea-fans. The mesoglea of many 

 octocoralla contains irregular calcareous spicules. 



The sea-pens (Pennatula'cea) usually form an elongated colony. The 

 stem, one end of which is embedded in the sand or mud of the sea bottom, 

 is supported by a calcareous or horny skeleton. The distal portion is dis- 

 tended like a feather and bears the dimorphic polyps. 



Fig. 22. Photograph taken with the camera submerged, to show 

 aquatic animals in their natural environment. In the background are seen 

 sea-fan and branching gorgonian. (Bull. U. S. B. F., 1907.) 



The sea-fans (Gorgona'cea) (Fig. 21) have a branched colonial axis formed 

 of horny or calcareous substance from the ectoderm, with spicules in the 

 mesoglea. 



In some cases the skeleton formed by the spicules forms a branched 

 axis, as in Corallium rubrum, or it may form a " series of connected tubes 

 for the individual, as in the organ-pipe coral (Tubip'ora) ." " The red coral 

 is found only in the Mediterranean Sea at a depth of from 10 to 20 fathoms." 1 



CLASS IV. CTENOPHORA 



The Ctenoph'ora, or " comb-jellies/' are so-called from 

 eight bands of comb-like cilia fused at their bases, which sur- 

 round their nearly transparent bodies. The body is non-con- 



1 Parker and Haswell's "Zoology." 



