20 



A BIOLOGY OF CRUSTACEA 



by the fine setae which project backwards from the inner edges of 

 the limbs to form a strainer between the median space and the 

 interlimb spaces. The main filtering region is near the bases of the 

 limbs where the flow into the interlimb spaces is greatest. 



During the backstroke (towards the tail) water is pressed out of 

 the interlimb spaces; much escapes via the tips and outer edges, 

 providing the thrust which propels the animal through the water. 

 Some water is also forced back into the median space, blowing 

 food particles off the setae. At the end of a backstroke two succes- 

 sive limbs become pressed closely together, because the rear limb 

 starts its forward stroke while the front limb is still moving back- 



FILTER SBTAE 



EXITS 

 OA OUTER FLAP 



Fig. i 6. Trunk limb of Artemia salina (Anostraca). The 

 limb is shown as it appears when flattened, but in life 

 it is bent as shown in the section in fig. 17. Note the 

 numerous intrinsic muscles which can alter the shape of 

 the limb. The detailed structure of the filter setae is too 

 fine to be shown. The line A-B gives the approximate 

 level of the section shown in fig. 17. 



