THE PHYLUM PORIFERA 



173 



Captured.- 



food 



pcLTticle 



Food particle 



being 



digested. 



Figure 9.1. Choanocytes from a sponge. The choanocyte at the left has just captured 

 a food particle. Adjacent cells show the movement of the food vacuole to the cell base 

 and its eventual transfer to an amebocyte. 



openings to regulate their size. Amebocytes accept food vacuoles (Fig. 

 9.1) from the choanocytes, and appear to play a dominant role in diges- 

 tion. As they crawl around, the nutrients are distributed throughout the 

 sponge. 



Sponges appear to have just two kinds of cells, the choanocytes and 

 the amebocytes. Some investigators describe as a third type persistent 

 embryonic cells that can become choanocytes, amebocytes or sex cells. 

 It is also possible that sex cells arise from amebocytes or choanocytes. 



Structural Types. The arrangement and complexity of the internal 

 channels vary considerably in different sponges. For convenience sponges 

 have been grouped in three structural types: (1) the asconoid sponges, 

 having the simplest organization, exemplified by the genus Ascon; (2) 

 the syconoid sponges, resembling in structure the genus Sycon; and (3) 

 the leuconoid sponges, having the most complex organization, named 

 after the genus Leuconia (Fig. 9.2). 



Osculum 



Incurnznt 

 / pores 



Internal 

 pore 



Fla^ellaied. 

 cha.Tntier 



E recurrent 

 channels 



Radia-l 

 canal 



Choa.nociyteS 



Pros opy les 



Apopyles 



Le-u-Conoid- 



AsconoidL Syconoid 



Figure 9.2. The three structural types of sponges. In each the choanocytes are shown 

 in black. 



