BRANCHIOPODA 363 



with the lower Branchiopoda in that their trunk limbs, of which there 

 are six pairs, are all alike and all strain food from the water, the 

 gnathobase projects, and the heart is elongate. The shell is well 

 developed and covers the trunk limbs. Sida, which may be taken 



add 



ram. 



ThA 



Fig. 243. Estheria ohliqua. From Caiman, after Sars. A, Shell of female, 

 from the left side. B, Male seen from the side after removal of left valve of 

 shell, add. adductor muscle; aw.' antennule; an." antenna; md. mandible; 

 ram. caudal ramus; Th. i, first thoracic limb. 



among weeds in pools in various, parts of Britain, is one of the 

 Ctenopoda. Penilia, one of the few marine cladocera, is another. 



The second tribe of the Cladocera, known as Anomopoda, contains 

 most of the genera of the suborder. Its members retain a well- 

 developed shell, but the trunk limbs, of which there are often only- 

 five, and sometimes only four, pairs, are highly differentiated for 



