A B I () L O (; V O F CKUS T A C E A 



the head. A few Cladocera have hecome predators with a reduced 

 carapace enabling the legs to seize prey. 



The Notostraca (fig. 5) have a different type of carapace which 

 only covers the upper surface of the front of the body. They are 

 odd in that the number of legs is not related to the number of 

 segments; there may be 26-34 segments, but up to 71 pairs of legs. 

 Although the general structure is so different from Lepidocaris, 

 the legs bear a distinct resemblance to the first three pairs of this 

 fossil (fig. 19, p. 27). The earliest definite fossil notostracans date 

 from the Permian (about 200 million years ago). These are so 

 similar to modern forms that they are placed in one of the two 

 modern genera, and a slightly later fossil, from the Triassic (about 

 180 million years ago) is considered as actually belonging to the 

 species Triops cancriformis which is widespread in Europe at 

 present. 



A recent discovery has been made in North America. Hutchin- 

 soniella macracantha (fig. 8b) is a very peculiar little crustacean, 

 living in soft mud in Long Island Sound; another species of its 

 group has been found in San Francisco Bay. It is uncertain exactly 

 where Hutchinsoniella fits in with the rest of the Crustacea, it has 

 been assigned to a separate sub class, the Cephalocarida, but it 

 undoubtedly has affinities with the Branchiopoda. 



The ostracods (fig. 6) are the most abundant of the early fossil 

 Crustacea, but most of them are not much help in tracing the 

 origin and evolution of the group. Like the Conchostraca the 

 ostracods have the body completely enclosed within a bivalved 



CLAWS OF 

 FURCA 



1ST MAXILLA 2ND MAXILLA 



Fig. 6. Heterocypris incongruens (Ostracoda), female with the left 

 valve of the carapace removed. Actual length 1.6 mm. 



