FEEDING, LOCOMOTION AND RESPIRATION 37 



Yet another method is used by Porcellana longicoriiis, which has 

 its third maxilliped fringed with long featherlike hairs which 

 stand out to form a spoon-shaped scoop. The crab swings these 

 scoops out sideways and spreads the setae out wide, then brings 

 them smartly back towards the other mouthparts entangling any 

 particles which happen to be suspended in the water. The second 

 maxillipeds brush the entangled particles out of the scoop and pass 

 them towards the mouth. 



A return to the production of a water current which has to pass 

 through a filter is made by Upogebia pugattensis. This species lives 

 in burrows and it produces a water current by the beating of its 

 pleopods. The filter is borne on the first trunk limb behind the 

 maxillipeds. Food trapped on this filter is combed off by the third 

 maxillipeds which in turn are cleaned by the second maxillipeds 

 and so on towards the mouth. 



The history of crustacean feeding mechanisms and attendant 

 modifications of locomotion and respiration, as outlined above, has 

 provided a complicated picture. The alternate losing and regaining 

 of filtering mechanisms make it look as if the Crustacea could not 

 make up their mind about which method of feeding they wanted 

 to specialise in. They have however been most successful in feeding 

 on both large and small particles, and the occasional return to 

 filter feeding by a representative of a group which feeds predomin- 

 antly on large particles is an indication of great ability to radiate 

 and to utilise all the assets that the environment can provide, rather 

 than of indecision about an evolutionary trend. 



LITERATURE 



Cannon, H. G. (1927). On the feeding mechanism of Neb alia bipes. 



Trans, roy. Soc. Edinb. 55: 355-369. 

 Cannon, H. G. (1928). On the feeding mechanism of the copepods, 



Calanus finmarchicus and Diaptomus gracilis. Brit. J. exp. 



Biol. 6: 131-144. 

 Cannon, H. G. (1933). On the feeding mechanisms of certain marine 



ostracods. Trans, roy. Soc. Edinb. 57 : 739-764. 

 Cannon, H. G. (1933). On the feeding mechanism of the Branchio- 



poda. Phil. Trans. B. 222 : 267-352. 

 Cannon, H. G. (1946). Nebaliopsis typica. Discovery Repts. 23: 213- 



222. 



