ARTHROPGbA, ; : ;; .";,-, 



a gizzardlike stomach containing teeth, and a straight 

 intestine. 



Crustaceans pass through a series of strange metamor- 

 phoses before reaching their adult form. They also 

 periodically cast the shell, or molt, every part of the 

 integument together with the lining of the gullet and 

 stomach being renewed ; and another remarkable endow- 

 ment is the spontaneous rejection of limbs and their 

 complete- 'restoration. Many species are found in 

 fresh water, but the class is essentially marine and 

 carnivorous. 



Of the numerous orders of this great class we will 

 mention only the following : 



1 . Phyllopoda ; small, almost microscopic, aquatic 

 Crustacea, with the appendages showing very little 



differentiation, no gastric teeth, the 

 body distinctly segmented and cov- 

 ered by a cephalic shield. The 

 a appendages posterior to the head 

 are leaflike, hence the name of the 



FIG. 56. - Water Fleas: a, 



Cyclops (after Vosseier) ; order. Included here are the brine 



b, Daphnia (after Vos- . . f . . N ' . 



seier); c, Cypris (after shrimp (Artemia), and the fresh- 

 water forms Branchipus and Daph- 

 nia, the bivalve shell of the latter giving it the appear- 

 ance of a mollusk (Fig. 56). 



2. Ostracoda; minute Crustacea with an unsegmented 

 body inclosed in a bivalve carapace or shell. This 

 order is represented in fresh water by Cypris (Fig. 56). 



3. Copepoda ; . mostly of small size, with an elongated 

 and, usually, a distinctly segmented body without dorsal 

 shell. In this order belong the fish lice, and the water 

 flea (Cyclops} of fresh water, the female of which is 

 often seen darting about in aquarium jars bearing its 

 two egg masses attached to the abdomen (Fig. 56). 



4. Cirripedia ; marine Crustacea, imperfectly seg- 



