98 



THE BIOLOGY OF MARINE ANIMALS 



coelomic pressures of Holothuria with those recorded for Thyone and 

 Caudina indicates that the stronger muscular contractions of these animals 

 during the course of burrowing necessitate the development of much 

 higher coelomic pressures. 



In holothurians which possess Cuvierian organs, e.g. Holothuria, strong 



■740 | 



< 



745^ 

 "o 



750^ 

 O 



755 £ 

 -160£ 



Time (minutes) 

 Fig. 3.4. Periodic Changes in the Volume of an Intact Holothuria grisea 



Time scale in minutes. Each cycle in the curve represents a series of about ten cloacal 

 contractions, increasing the body volume by 10-15 ml, followed by a contraction of the 

 body wall. Each contraction of the cloaca drives in about 1 ml; when the body wall 

 contracts, all of the accumulated water is driven out and the volume falls. (From 

 Pantin and Sawaya (101).) 



'-0 



-i-J 



3 - 



Maxima./ response 

 to touch 



Active 

 elongation 



Bending and 

 elongation 



10 15 



Time (minutes) 



20 



25 



Fig. 3.5. Graph of Changes in Coelomic Pressure of 

 Holothuria grisea (From Pantin and Sawaya (101).) 



contractions of the body wall can lead to rupture of the cloaca and extru- 

 sion of the Cuvierian organs. This is usually attended by high coelomic 

 pressures (12-18 cm H 2 0). But extrusion of the gut can sometimes occur 

 at moderate pressures, and does not invariably involve high pressures. 

 Consequently other factors besides development of high coelomic pres- 

 sures must be involved (29, 36a, 101, 108). 



