214 



INVERTEBRATE ZOOLOGY 



body of the host and swim free in the water. In contrast with 

 these stand some other parasitic copepods the bodies of which 

 have become so greatly reduced as an adaptation to the parasitic 

 habit that they are more Hke a simple worm in appearance than 

 like an arthropod. It is only through the unaltered larval 

 stages, the nauplius and the metanauplius, that the affinities 

 of these degenerate adults are recognizable. 



Subclass OSTRACODA 



Ostracoda are abundant in various fresh- and salt-water 

 habitats. The entire animal is enclosed within a bivalve shell 



First antennae 

 \ Sernvd antennae 

 \ \ Eye 



Branchial Plate of Mandible 

 1 Stomach 



Fuod hnlls 



Branchial setae 

 Intestine 



Ovary 



Dorsal seta 



— Sub-terminal clatv 



Terminal claw 



\ '•Terminal aeiu 

 . Mandibular palp ^^ Firstfoot 



Labrum Branchial plate of maxilla 



Fig. 99. — General anatomy of an ostracod, Cypris virens Jurine. (After 

 Vavra) . (Reprinted by permission from Ward and Whipple's Fresh-water Biology, 

 published by John Wiley and Sons, Inc.). 



Natatory setae 



(Fig. 99), but when the valves open the appendages protrude. 

 Segmentation of the body is very indistinct or wanting. The 

 head region bears two pairs of antennae, both used in swimming; 

 the mandibles; and two pairs of maxillae. Ordinarily, the trunk 

 region bears but two pairs of legs. 



Most ostracods are omnivorous. Both parthenogenetic and 

 true sexual reproduction occur. The eggs produce nauplii which 

 undergo a number of molts before reaching the mature form. 



