464 EVOLUTION OF ANIMALS Part V 



oscula 



mBm^ 





Fig. 22.10. Commercial sponge, Hippospongia, a typical sponge of commerce. 

 When cut open, living sponge looks like raw liver. The chief American region for 

 sponges is the west coast of Florida, centering at Tarpon Springs. The skeletons 

 of commercial sponges are composed entirely of spongin fibers that are horny and 

 elastic. The preparation for market consists of removing all soft matter and bleach- 

 ing the skeleton. (Courtesy, Brown: Invertebrate Types. New York, John Wiley 

 and Sons, 1950.) 



greatly reduced. The sponge-fishing grounds of Florida and the Bahamas have 

 been overfished and sponges are subject to diseases which occasionally reduce 

 the growth for long periods. 



Comparisons with Other Phyla 



Likenesses 



Simple sponges resemble the colonial protozoan, Proterospongia. 



Collared cells of sponges are similar to those in Proterospongia and some 

 other protozoans. They occur nowhere else among animals. 



The wandering amebocytes of the mesenchyme of sponges are similar in 

 habit and form to amebas. 



The tube-shaped body, the colonial habit and attached state of sponges are 

 suggestive of the corals (Phylum Coelenterata). 



Differences 



The characteristic spicules of sponges are different from skeletal structures 

 in any other animals. Sponges differ from protozoans in that their cells are 

 more dependent upon one another than the cells of colonial protozoans. They 

 differ from other multicellular animals in that their cells are less dependent 

 upon one another. 



