166 



THE BIOLOGY OF MARINE ANIMALS 



of acorn barnacles are not accelerated by decreased 2 or increased C0 2 

 tension in the water. Both decrease in 2 and increase in C0 2 quicken the 

 rhythm of respiratory movements in Gammarus locusta but the effects are 

 transitory. In amphipods and isopods generally, respiratory movements 

 are performed by beating of pleopods, and the rate is accelerated by low 

 2 and high C0 2 tensions in most subaquatic species examined (Cirolana, 

 Cymodoce, Idotea, Melita). 



Ventilation in stomatopods is accomplished both by beating of the 

 pleopods and movements of the thoracic branchiae, and in Squilla these 



sec 



12 3 4 5 6 



Time (hours) a.fter Low- tide Period 



Fig. 4.14. Curves Showing the Course of Oxygen Utilization and Velocity 

 of Respiratory Current after a Low-tide Period of 20 hours in the Gaper 



Mya arenaria 

 Current velocity = 1/streaming time. (From van Dam (29).) 



movements are quickened by lack of 2 and heightened C0 2 . In decapods 

 oxygen lack is sometimes effective as a stimulus increasing respiratory 

 movements (Pandalus, Eriocheir, et «/.), and increased C0 2 is also accelera- 

 tory. Exceptions are the shore crab Carcinus maenas and the lobster 

 Homarus vulgaris. Oxygen withdrawal (utilization) in general is rather 

 high, between 25-88% (average value about 50%) (Fig. 4.10) (76, 77, 90, 

 100, 120, 150, 151, 154). 



The abdominal appendages in Limulus perform ventilation movements 

 at a frequency of 25-50 beats per min. Respiratory movements are con- 

 trolled by branchial ganglia in the ventral nerve cord, and are influenced 

 by a variety of internal and external stimuli. Anoxia leads to a steady 



