THE INVERTEBRATE LEGIONS 89 



live in symbiotic relationship in the tissues of a wide variety of invertebrates, 

 especially in corals, jellyfishes, and radiolarians. These species are known 

 collectively as "zooxanthellae" and are small, degenerate, photosynthetic animals 

 which live and multiply in the tissues of their host. They are able to live free 

 of the host, but rarely do so. Zooxanthellae use the carbon dioxide, phosphorus, 

 and nitrogen wastes of the hosts in order to synthesize food. They yield oxygen 

 to the host and may even be digested by the host when the latter is hungry 

 (Hyman, 1940). The brownish or yellowish color of corals and radiolarians 

 is due to the presence of zooxanthellae. Some coral animals are greenish, and 

 this is due to the presence of zoochlorellae, small, single-celled green algae that 

 live in the hosts' tissues in the same way as do zooxanthellae. 



Amoebalike Protozoans: Class Sarcodina or Rhizopoda — Figure 23 



Among the most delicate and beautiful objects of the sea as well as the 

 largest protozoans belong to this group. All of the species have extensions of 

 their bodies called "pseudopodia " ("false feet") by which they move and 

 capture food. Pseudopodia are neither constant in form nor number, but are 

 best thought of as being tentaclelike extensions which may appear or disappear 

 at any place on the body. How pseudopodia are formed by the protozoan is 

 not known. 



The foraminiferans ("hole bearers") are a group of amoebalike protozoans 

 that build calcareous skeletons which are perforated by many minute holes 

 through which the slender pseudopodia extend. The animal starts life with a 

 small shell of one chamber. New chambers of ever-increasing size are added, 

 usually in a spiral fashion (like the growth of snails) until the time of death. 

 Foraminiferans are found in immense numbers from surface waters to the 

 abyssal zone. Their skeletons have accumulated in huge quantities in oozes 

 on the sea bottom. One form, Glohigerina, has covered 30 per cent of the 

 forty million square miles of ocean floor with its shells (Buchsbaum, 1948). 

 The chalk of England's Dover cliffs, a thousand feet thick, is composed largely 

 of foraminiferan shells. If one considers that upwards of fifty million shells may 

 occur in one pound of bottom ooze, the number of shells on the sea bottom 

 becomes inconceivably great. 



Radiolarians are like foraminiferans, but have siliceous skeletons. They have 

 yellow-brown zooxanthellae in them, which probably contribute to their 

 nutrition. The delicate and frequently very beautiful skeletons, as well as oil 

 or fat droplets in the body, and the fine pseudopodia aid these animals in floating 

 at the surface of the ocean. In the very deep parts of the ocean (over 15,000 

 feet), radiolarian oozes are formed of the skeletons of these animals. Somewhat 

 less than 5 per cent of the ocean floor is carpeted by this ooze. At these depths, 

 the calcareous skeletons of foraminiferans dissolve, leaving onlv the relatively 

 insoluble siliceous skeletons of radiolarians. 



Giliates: Class Ciliata — Figure 23 



Ciliates are named and distinguished from all other protozoans by the 

 possession of little hairlike processes called "cilia" which cover their bodies. 

 Most are free-swimming, but some live attached to substrate or are colonial. 



