48 



PORIFERA 



c. Leucon — external opening to canals, through orifices leading 

 through ectoderm to endoderm. The water comes in the 



incurrent canal, then 

 into the radial, then 

 to the paragastric 

 cavity. The radial 

 canals are lined with 

 Jiagella; all whip 

 down and suck the 

 water in. 

 3. The general symmetry 

 o f t h e embryonic 

 gastrula stage is re- 

 tained in the adult. 



Distribution. — The ma- 

 jority of the sponges are 

 marine, but there are a few 

 fresh water forms (Spon- 

 gillidae). They are found 

 attached to rocks, sea weed 

 and submerged objects. 

 The true horny sponges are 

 found in shallow water, not 

 deeper than 450 fathoms. 

 Other forms are found at 

 great depths. 



Pigment in Sponges. — 

 Many sponges contain pig- 

 jnent. The lipochrome 

 pigment zobyierythrin (seen 

 in lobsters) is common. 

 The green pigment of the 

 fresh water sponge, analo- 

 gous to chlorophyll, prob- 

 ably aids in holophytic 

 nutrition. 



Sponges vary in color 

 from red brown to bright 

 colors with pronounced 



Fig. 18. Top, commercial sponge. Center, 

 the finger sponge. Bottom, red sponge. (From 

 A. G. Mayer, SeasJiore Life. Courtesy of N. Y. 

 Zool. Soc.) 



