2 6o CLASSIFICATION OF ANIMALS 



is also frequently applied to the group because the chitinous 

 cuticula is impregnated with salts of lime which render it very 

 hard. The appendages are forked (biramous) and at least 

 three pairs are modified as mouth parts and two pairs, the 

 antennae, have a sensory function. 



559. The orders Phyllopoda, Ostracoda, Branchiura and Copepoda com- 

 prise only small forms, seldom more than an inch in length and usually 

 minute. The Phyllopoda are characterized by their broad, leaf-like swim- 

 ming appendages. The Ostracoda have a carapace in the form of two 

 valves, like the shell of a clam, which can be opened and closed. The 

 Copepoda are cigar shaped and have a single median eye. The Ostracoda 

 and Copepoda are very common in our fresh-water ponds. The Bran- 

 chiura are parasitic in the gill chambers of other Crustacea and on fishes. 

 There are also many parasites among the Copepoda. 



FIG. 149. A shrimp, Palaemonetes vulgaris. (From Galloway, after Verrill.) 



560. Order 5. The Cirripedia are the barnacles. They are all marine. 

 The young are free swimming but they come to rest and attach them- 

 selves to some object. A series of calcareous plates are formed by folds 

 of the skin. Some of these are hinged and can be moved by muscles. 

 The animal may be entirely enclosed by the shell. The appendages are 

 long and slender and are fringed with hairs. These organs are thrust out 

 into the water and by a sweeping motion currents carrying food particles 

 are directed toward the mouth. The eyes are degenerate in the adult 

 but the reproductive organs are highly developed. The barnacles are 

 usually hermaphrodytic. Several families belonging to this group are 

 parasitic. The sacculina described in Part III is a notable example. 



