150 



THE BIOLOGY OF MARINE ANIMALS 



have also been described in various crabs for renewing air in the branchial 

 lungs (24, 122). 



Adaptations for aerial respiration are not infrequent among freshwater 

 fish inhabiting waters which are periodically subject to oxygen depletion, 

 but in marine fishes they are limited to some inhabitants of tropical shores. 

 Shore gobies {Periophthalmus and allies) are commonly seen in mangrove 

 swamps jumping actively over the mud when the tide is out. In conjunc- 

 tion with their partially terrestrial habits the branchial chamber is enlarged 

 and modified as a gas storage organ for aerating the gills. Gill surface 

 relative to body surface is reduced in littoral gobies compared with aquatic 



TABLE 4.2 

 Gill Reduction in Crustacea from Aquatic to Terrestrial Species 



(After Pearse) 



1 Determined from material hardened in chromic acid. 



forms. In Periophthalmus the gills are supplemented by branchial diverti- 

 cula, and the mucous epithelium of mouth, pharynx and branchial cham- 

 bers is well vascularized. By rhythmic movements of the buccal region the 

 air stored in the bucco-pharyngeal cavities can be renewed. Paired pharyn- 

 geal sacs are found in the cuchia Amphipnous, a brackish- and freshwater 

 fish of tropical Asia. The gills are greatly reduced in this animal, which 

 apparently depends upon aerial respiration (108, 118, 166). 



RESPIRATORY EXCHANGE 



Apart from anaerobes, animals ultimately require oxygen for oxidizing 

 reactions yielding energy during catabolism. Metabolism embraces the sum 

 total of energy transformations taking place within an organism. In aerobic 

 animals, therefore, the level of oxygen consumption provides an indirect 

 index of metabolic rate (indirect calorimetry). The standard term for des- 

 cribing metabolism is the calorie; direct determination of metabolism in- 



