I. CRUSTACEA: CIRRIPEDIA 



371 



Sub Class IV. Ostracoda. 



Like the Cladocera and the Estheriidoe the Ostracoda are enclosed 

 in a bivalve shell, which, when closed, includes not only the body but the 

 head and appendages as well, these being protruded when the shell is 

 opened. The valves are closed by an adductor muscle, opened l^y a 

 hinge ligament like that of lamellibranchs. This resemblance to the 

 molluscs is heightened by lines of growth upon the shell. The antennae. 



Fig. 3S9. — Cypris fasciatus, adult female (after Claus). I-IV, appendages; c, furca; 

 e, eye; I, liver; m, adductor muscle of shell; 0, ovary; s, shell gland. 



the first simple, the second frequently two-branched, are used for swim- 

 ming and creeping. The mandibles, maxillae, and three pairs of legs 

 vary greatly from genus to genus. The internal structure is also variable. 

 The Ostracoda are bottom forms and live in fresh and brackish water 

 as well as in the sea. 



Cypridinid^. First two pairs of legs maxillary in character, the last de- 

 veloped into a hook for cleansing the shell; heart present; marine; Cypridina* 

 Cypridid^. First pair of legs maxillary in character; heart lacking; fresh 

 water. Cypris * Candona.* 



Sub Class V . Cirripedia. 



The barnacles differ from all other Crustacea in that they have lost 

 their locomotor powers and live attached to rocks, floating timber, and 

 the like. In some cases they attach themselves to other animals, as crabs 

 and molluscs, or, as in the case of Coronula and Tubicinella, to whales. 

 This leads in Anelasma and the Rliizocephala to a true parasitism, the 

 barnacle not only attaching itself to an animal but sucking its juices as 

 food. 



The attachment is by the dorsal surface in the neighborhood of the head, 

 and is initiated by the first antennae, in which is a cement gland secreting 

 a rapidly hardening cement. The fiat region of fixation in the Balanidae 



