GRANTIA (A Marine Sponge). 



Phylum II, PORIFERA; class i, PORIFERA; order 2, HETEROCOELA. 



HABITAT. Sponges are found in all seas, and at all depths from 

 low tide mark to the deepest abysses yet dredged. The group is also 

 represented in fresh-water streams and lakes by one family (Spongil- 

 lidae). Grantia is a non-colonial sponge common along the New 

 England coast. It is attached to rocks, submerged piles, or other 

 objects. 



Technical Note. Specimens of Grantia for laboratory use can be pre- 

 served in alcohol or formaldehyde. Place one of the sponges in a 

 watch glass partly filled with water and examine under a low power 

 of the dissecting microscope. 



EXTERNAL FEATURES. It will be observed that this type of sponge 

 is nearly cylindrical, though usually tapering somewhat toward the 

 base the end which was attached. The free end is crowned by a 

 circlet of glistening spicules surrounding the excurrent opening or 

 osculum. The entire surface of the sponge seems to be covered 

 with a fuzzy growth, which is in reality a bristling mass of finer and 

 shorter spicules arranged in tufts forming polygonal patterns, as will 

 be seen under higher magnification. These spicules and others which 

 are imbedded in the walls of the sponge form its skeleton or supporting 

 frame-work, the real living substance being of a gelatinous nature. 



Growing out from the side of some of the larger specimens, especially 

 near the base, you may notice one or more buds outpushings of the 

 three layers of the body wall which will in time become separate 

 individuals. 



Exercise i. Draw a sponge natural size and one enlarged two or three 

 times. 



Technical Note. With a sharp scalpel or a section razor split a sponge 

 lengthwise into two halves. A dried specimen will be best for this 

 purpose. Study the cut surface and note: 



2 II 



