224 



SYSTEMATIC ZOOLOGY. 



FIG. 51. Cypris herricki, an 

 ostracode, enlarged After 

 Turner. 



ORDER III. OSTRACODA. 



These forms are enclosed in a 

 firm bivalve shell into which all 

 parts can be retracted and the 

 valves closed like those of an 

 oyster or clam. These forms are 



<?rnQ -|l nn l v Q fr^pfinn of an irir>h 

 Small, ' miy a . 



in length. They abound in the 

 bottoms of fresh-water ponds and in brackish water. 



ORDER IV. CIRRIPEDIA (Barnacles). 



In the Barnacles the body is usually enclosed in a 

 calcareous shell composed of a number of parts, the shell 

 being directly attached to some 

 solid support, as in the acorn bar- 

 nacles so common on the rocks at the 

 shore, or there is a fleshy stalk, as 

 in the goose - barnacles (fig. 52). 

 At one place the shell gapes and 

 from this opening the six pairs of 

 two-branched feet are protruded with 

 a sweeping motion. These feet are 

 finely haired and the interlacing 

 hairs make a fine net which strains 

 minute forms from the water and 

 carries them to the mouth inside the shell. The calcare- 

 ous shells caused the barnacles to be regarded as molluscs 

 for a long time, but the nauplius stage in development, 

 the two-branched jointed feet, and other features pro- 

 claim them truly crustacean. 



FIG. 52. Goose - barna- 

 cles (Lepas anatifera). 

 After Schmarda. 



Mention should be made here of a large group of extinct 



