52 PORIFERA 



A compact orange-colored sponge {Suberites domunculd), of 

 peculiar odor, grows around the shell inhabited by a hermit crab 

 and dissolves the shell substance. Algae live in sy?nbiosis with some 

 sponges. A cuttlefish {Rossia glaucopis) (see MoUusca, p. 154) puts 

 its eggs in pockets in the substance of a siliceous sponge. 



Economic Importance. Positive. — i . The uses of the sponge are 

 too well known to more than mention that they are of great im- 

 portance in hospitals, homes, factories and garages. 



2. As an industry, sponge fisheries are of great value, probably 

 being worth nearly two million dollars annually. In 1926 they 

 brought in (Florida fisheries alone) $666,093.00. 



3. The siliceous sponges form flint deposits. 



Negative. — i. Sponges may kill oysters by boring into them. 

 (Boring sponges.) 



2. They may attach to the oysters and starve them by taking the 

 food first. 



3. They may actually reduce the oxygen of the water in their 

 immediate vicinity by using currents first. 



4. Sometimes /r^j-A water sponges are of serious injury in that 

 they attach to the walls of reservoirs and water pipes, and oflFer 

 lodgment for fresh water mussels and Bryozoa. Various algae 

 accumulate and the debris lodging against the miscellaneous or- 

 ganisms produces a felt-like mass called " pipe-moss." 



5. The United States Department of Agriculture has published 

 a bulletin on the reclamation of soil in Florida marshes showing that 

 the sponge spicules wear away the hoofs of the mules used in plow- 

 ing, while the shoes of the plowmen are worn through and their feet 

 rendered raw in one day. 



Fossil Relatives. — Fossil sponges similar to existing groups have 

 been found in formations from the Cambrian period down. They 

 are chiefly found in chalk and flint. 



It has been estimated that a mass of sponge skeletons may give 

 rise to beds of flint nodules in the space of fifty years. Siliceous 

 sponges derive their spicules from small quantities of silicate in the 

 sea water, originating from the decomposition of igneous rocks such 

 as granite. The sponges and the Radiolaria (see page 44) furnish 

 siliceous skeletons to aid in flint formation. The siliceous chalks 

 are the first stage in the formation of flint. There is evidence from 

 the casts of spicules found that the silica of sponge skeletons 

 actually dissolved and was then redeposited. 



