CHAPTER II 



The Sponges 



{P/iylfif// Porijcni) 



Limy and glass sponges 



k_7PONGES are more widely known from their 

 cleaned and dried skeletons than they are as living 

 creatures that flourish in all the seas of the world or 

 encrust rocks and sticks in fresh waters. Familiarity 

 with sponges through enjoying the luxury of a fine 

 soft Mediterranean bath sponge or scrubbing a wall 

 with a sturdy but elastic sheepswool sponge from 

 Florida waters is hardly good preparation for recog- 

 nizing such animals in the flesh. Peering over the 

 edge of a boat in twenty feet of water, one sees on 

 the clear, sunlit bottom an ugly black ball, somewhat 

 larger than a grapefruit and with an uneven bumpy 

 surface. If there is someone aboard who can manipu- 

 late a twenty-five-foot pole without being pulled 

 overside, it becomes a simple matter to hook onto 

 the sponge with the curved metal prongs that pro- 

 trude from the far end of the pole and to pull the 

 living animal from its firm mooring on the sea bot- 

 tom, delivering it wet and glistening into the boat. 

 Now it is seen to have a number of large openings 

 through the jet-black leathery membrane that cov- 

 ers the surface. And if the sponge is sliced open the 

 halves reveal cut surfaces that look like nothing so 

 much as raw, slimy, dark-brown beef liver. What 

 superficially resemble bile ducts are tangential sec- 

 tions of the main channels through which water is 

 ejected out the large openings noted at the top of the 

 sponge. Not apparent except on very close examina- 



tion are the millions of microscopic pores that pierce 

 the whole of the outer surface and through which 

 water is sucked into the sponge when it is on the sea 

 bottom and feeding by straining microscopic plants 

 and animals out of the water. The steady stream that 

 passes through the body into the many small pores 

 and out the few large vents at the top also serves to 

 bring oxygen to the internal cells of the sponge and 

 to carry away their wastes. 



The volume of water filtered by a good-sized 

 sponge is tremendous. One estimate set the rate of 

 active flow for a Bahaman wool sponge at about two 

 quarts a minute, and perhaps several hundred gal- 

 lons in twenty-four hours. To add one ounce to the 

 weight of a growing sponge, as much as a ton of wa- 

 ter may have to be filtered. The rate of flow can be 

 diminished or stepped up, depending upon the condi- 

 tion of the water, by contraction of the vents or by 

 opening them wide. The surface pores are less re- 

 sponsive than the vents and usually close only under 

 injurious conditions. 



The external pores, for which the phylum of 

 sponges has been named the Porifera or "pore bear- 

 ers," are represented in the dried bath sponge only 

 by the few large vents, the small apertures having 

 been stripped away with the removal of the flesh. 

 And the extraordinary porosity of the skeletal net- 

 work represents only the remnants of the complex 



561 



