CTENOPHORA 



31 



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

 in all seas, both in shallow water and at great dejjths. They inchule 

 the organ-pipe coral, the precious red coral {('(imllium rubniin) of the Medi- 

 terranean Sea, and the sca-jx'iis and the sea-fans. The mesoglea of many 

 octocoralla contains irri'^;iilar calcareous spicules. 



The sea-pens {Pvini(ili(l(i'nin 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 ectpderm, with spicules in the 

 mesoglea. 



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

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

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

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



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- 



^ Parker and Haswell'.'* "Zoology." 



