CLADOCERA. 



299 



ij seg- 



Fig. 240.— Actheres of the trout 



The highest members of the group of sucking Entomo- 



straca are Caligus and Argulus, in which the body 



mented, with antennae and free 



mouth-parts and legs ; the latter 



genus with compound eyes. Cali- 

 gus curtus MtlUer lives on the cod, 



and Argulus alosce Gould on the 



alewife. 



Order 3. Brancliiopoda. — This 



order includes such Crustacea as 



in the higher forms breathe by 



rather broad feet. There is a con- 

 siderable range of 

 form from the 

 Ostracoda, repre- 

 sented by Cypris, 

 in which the feet 

 are much as in Cy- 

 clops, through Daphnia and Sida (Fig. 242) 

 which represent the Cladocera, up to the 

 Phyllopods. The suborder of Ostracoda 

 {Cypiris) arebivalved, the shell often thick. 

 They have two eyes, two pairs of autennse, 

 a pair of mandibles with a jointed feeler 

 (palpus) and a gill, and four pairs of feet, 

 the second pair often carrying a small gill. 

 The shells of certain species allied to Cypris 

 abound in the lowest Silurian strata. The 

 species live in fresh-water pools and in the 

 ocean at various depths. They undergo no 

 metamorphosis, the youngest stage being a 

 shelled Nauplius. 



The suborder Cladocera is represented by 

 fresh and salt-water species. The higher 

 forms are Sida and Daphnia. They are 

 called water-fleas from their jerky motions. 

 The eggs of Baplmia are borne about by 

 the females in so-called brood-cavities on 

 the back under the shell. There are two 





Fig 241.— Penella of 

 the sword-fish, female. 



sorts of 



I. e. 



the " summer" eggs, which are laid by 



