Respiration 109 



I. Water Crabs with Large Inhalent Opening: portunids such as Scylla, 



Neptunus, Thalamita. 

 II. Transition Breathers without Large Inhalent Opening: 



L Pumpers: Pump water out of branchial chamber. Sesarma, Ilyoplax, 



Metaplax, Macrophthalmus. 

 2. Non-pumpers: Circulate air through water in branchial chamber. 



a. Having normal course through branchial chamber. Grapsus, 

 Potamon. 



b. Having special respiratory openings between 3rcl and 4th legs. 

 Uca, Ocypode. 



There are land crabs (Gecarcinus, Cardisoma) which do not carry 

 water in their gill chambers, and the respiratory cavities of Ocypode 

 are not completely filled with water (Pearse, 1929) . 



As aquatic crabs take up life on land, various changes take place 

 in their respiratory organs (von Raben, 1934). Often the gill cover 

 takes on greater respiratory functions and in some cases becomes 

 quite vascular, even developing lacunar systems which are sur- 

 rounded by capillaries. The chitinous covering of the gills tends 

 to become thicker. There are mechanisms for keeping the gill plates 

 moist; in some cases water passes from the mouth through a special 

 canal to the gills. Some land crabs breathe through vascular areas 

 on the abdomen. And beach-skipping gobies breathe in part through 

 their tails (Roughley, 1947). 



Marine mollusks are for the most part gill-breathers, but a few 

 littoral species have become air-breathers. River snails are com- 

 monly water-breathing, but in swamps and marshes air-breathing is 

 the rule, and land snails are generally pulmonates. 



Annelids which live in tubes or in stagnant water often develop 

 gills, which are comm.only evaginations of the skin. In the swamps 

 of the Gran Chaco, Carter & Beadle (1931a) studied methods of 

 respiration in eight species of oligochaetes. They do not believe that 

 any of these worms can live anaerobically, but that all are able to 

 endure low oxygen contents in the medium in which they live. Ont 

 Aelosoma lived in the narrow oxygenated surface stratum, building 

 a tube attached to plants. One large species (Drilocrius) burrowed 



