372 



THE BIOLOGY OF MARINE ANIMALS 



Somewhat different kinds of effector organelles are found in certain 

 other protozoans. In the dinoflagellates Polykrikos and Nematodinium 

 there are trichocysts that have considerable resemblance to the nemato- 



Cirdle 



Fig. 9.2. Nematocysts of Protozoa 

 Nematocyst of dinoflagellate Polykrikos, (a) discharged, (6) undischarged, (c) ripe 

 spore of a myxosporidium Myxobolus, showing two nematocysts, left undischarged, 

 right discharged, (d) Nematodinium, a dinoflagellate containing nematocysts. (From 

 various sources.) 



cysts of coelenterates (Fig. 9.2). They are oval capsules surmounted by a 

 cap and containing a slender spirally coiled thread. Various chemical 

 agents cause these nematocysts to discharge, but their normal function is 

 unknown. The polar capsules of Cnidosporidia (Sporozoa) also resemble 

 the coelenterate nematocyst. They are oval bodies containing a long coiled 



