290 



COMPARATIVE ANATOMY 



CHAP. 



at*. 



e*i- 



one pair of ostia. Mostly in 

 fresh water. Daphnia (Fig. 

 192), Sida, Moina, Lynceus, 

 Polyphemus, Leptodora, Evadne 

 (marine). 



Order 2. Ostracoda. 



Body small, consisting of 

 few segments indistinctly seg- 

 mented, with bivalve shell. 

 Besides the 5 pairs of well- 

 developed limbs to be attri- 

 buted to the head, viz. the 

 antennae, mandibles, and max- 

 illae, all or some of which may 

 be developed as creeping or 

 swimming feet, we find only 2 

 pairs of trunk limbs. The 

 heart may be present or want- 

 ing. Fresh-water form : Cypris. 

 Marine forms: Cythere, Halo- 

 cypris, Cypridina (Fig. 193). 



Order 3. Copepoda (with 

 biramose or rowing feet). 



Sub-Order 1. Eucopepoda. 



Body small, mostly dis- 

 tinctly segmented, without 

 shell fold. The trunk consists 

 of 10 segments, the 5 anterior 

 carrying 5 pairs of biramose 

 rowing feet, while the 5 pos- 

 terior are limbless. The fore- 

 most trunk segment is fused 

 with the head. Antennae, 

 mandibles, and maxillae (the 

 two branches of the posterior 

 maxillae separated from one 

 another) are well developed, at 

 any rate in the free -living 

 forms. The mouth parts in 

 the parasitic forms either suck 

 or pierce. Heart sometimes 

 wanting ; when present it is 



Fig. 194 Clausocalanus mastigophorus (Glaus), female, from the ventral side (after an 

 original drawing by W. Giesbrecht). Only the extremities of the left side of the body are 

 depicted 01 Anterior, 03, posterior antennse ; md, mandible with masticatory ridge fc; TO*,, 

 anterior maxilla ; mx^a, mx^b, anterior and posterior maxillipedes = endopodite and exopodite oft 

 second maxilla ; t r t t , rowing feet (biramose), t s , rudimentary ; /, frontal organ ; r, rostrum ; au, 

 eye o upper lip; m, mouth; u, under lip; c+J, head and 1st trunk segment; JI-A', 2d-10th 

 trunk segments; I-V, limb-bearing segments (thoracic segments) ; Vl-X, limbless segments (abdo- 

 minal segments); VI+VII, genital double segment; go, genital aperture; es, ovisac (unpair 

 /, fur ex. 



