PHYLUM PORIFERA 129 



Economic Relations 



Many sponges are beneficial to man, and there are a few wliich 

 are detrimental. Oysters and some other Mollusca are injured or 

 destroyed by certain sponges which attach themselves to the mol- 

 lusc's body or by others which bore through its shell and thus 

 kill it. 



Of positive importance, lesser items include the large flint de- 

 posits from siliceous spicules of some species and those used for 

 ornaments. The chief importance lies in the use of the spongin 

 skeletons of certain groups for bath and surgical sponges. With 

 rapid industrial development sponges have also become useful as 

 a fabric material. The demand has brought about the establishment 

 of sponge farms where they are raised from fragments about an 

 inch square or slips, like plants. Selected sponges of good quality 

 are cut up, and the pieces fastened to hooks or wire on a weighted 

 frame. The "seeded" frame is sunk in the ocean and left for a 

 year or two for the sponges to grow. If everything has gone as 

 expected, the slips will then be marketable. 



Sponges are usually harvested by diving or hooking between May 

 and October. Dredges which are sometimes used for this purpose 

 are not very satisfactory, because they drag down and kill so many 

 young sponges. Sponges die quickly when taken. They are allowed 

 to rot for a day or two, then beaten and squeezed under water, 

 washed, dried, and sometimes bleached. Next they are trimmed, 

 sorted, and placed on the market. The value of the crop each year 

 is at least $5,000,000. Most of the commercial sponges come from 

 the Mediterrajiean Sea, Red Sea, coasts of Florida, the Bahamas, 

 the West Indies, and Central America. 



Phylog-enetic Advances of Sponges Wlien Compared With Protozoa 



This group appears to be somewhat advanced over the Choano- 

 flagellata of the Genus Proterospongia in Class Mastigophora. In 

 sponges the cells are partially organized into layers and are differ- 

 entiated for separate functions. Sexual reproduction is developed 

 here in a simple way. The group has advanced so little that little 

 else can be said. 



