550 ZOOLOGY SECT. 



ORDER 2. NOTOSTRACA. 



Branchiopoda in which there is a large dorsal shield-shaped 

 carapace. The eyes are sessile. The antennae are reduced. There 

 are 40 to 63 pairs of trunk appendages. The caudal styles are 

 many- jointed. 



Including Apus and Lepidurus. 



ORDER 3. CONCHOSTRACA. 



Branchiopoda with a carapace divided into two lateral portions 

 or valves like the shell of a bivalve mollusc, and enclosing the 

 entire animal. The antennae are biramous and are used as 

 swimming appendages. The eyes are sessile, coalescent. The 

 appendages of the body-segments number 10 to 27 pairs. The 

 caudal styles are in the form of un jointed, curved claws. 



In this order are included Estheria, Limnetis (Fig. 455), and one 

 or two other genera. 



ORDER 4. CLADOCERA. 



Branchiopoda of small size with a bivalved carapace which 

 encloses the trunk but not the head. The eyes are sessile and 

 united together. The antennae are biramous and used as 

 swimming appendages. Only 4 to 6 trunk appendages ; caudal 

 styles unjointed, claw-like. 



To this order belong Daphnia, Polyphemus, Leptodora (Fig. 

 456), etc. 



Sub-Class II. Ostracoda. 



Crustacea with unsegmented or indistinctly segmented body, 

 bearing not more than four pairs of appendages on the trunk, the 

 limbless posterior part provided with a pair of caudal styles. 

 There is a well-developed bivalved carapace. Paired eyes may be 

 present or absent. Both antennules and antennae are used in 

 swimming ; the latter are generally biramous. The mandibles 

 have a palp. The young escapes from the egg as a nauplius. 



In this sub-class are comprised Cypris, Cy there, etc. (Fig. 457). 



Sub-class III.--Copepoda. 



Crustacea with elongated, distinctly segmented body, bearing 

 usually five pairs of limbs, the last four having the character of 

 biramous swimming appendages, sometimes with a sixth pair 

 which may be vestigial : the posterior region (abdomen) without 

 appendages, provided with a pair of caudal styles. The cephalic 

 dorsal shield is not extended backwards, but usually coalesces with 

 the exoskeleton of the first (and sometimes also the second) body- 

 segment. Paired eyes are absent except in the Branchiura. Both 



