730 ARTHROPODA phylum vii 



Subclass B. EUCRUSTACEA Kingsley/ (Crustacea proper.) 



Crustacea having typically two pairs of antenniform preoral appendages and at 

 least three pairs of pastoral appendages acting as jaws. 



In the Crustacea proper the appendages of the head-region are as follows : 

 the first and second pairs are preoral and are known respectively as antenmiles 

 and antennae; the third pair, placed on either side of the mouth, are the 

 mandibles ; the fourth pair, maxillulae, and fifth pair, maxillae (the two pairs 

 sometimes known as first and second maxillae), are secondary jaws. The 

 appendages behind these vary in character, some being walking or swimming 

 feet, while from one to three pairs may be subsidiary to the maxillae in 

 feeding, in which case they are called maxillipeds. 



Regarding the evolution of the subclass, Bernard has reached the conclusion 



' 



Strabops ' ' 



Sidney 



Amiella 

 Aglaspis 

 Molaria 



Emeraldella - 

 Habelia 



H 



canchoiha 



Yphoia 



Nathorstia 



••Mauella 



Belitna . 



/ 



Waptia 

 ^Naraoia 



Bidentia 



^Hymenocaris 



, Opabinia 



Theoretical Evolution of Cambrian Crustacea from the Branchiopoda 



(according to Walcott"). 



that all Eucrustacea are descended from a browsing carnivorous annelid with 

 its first five segments (head) bent so that its mouth faced ventrally and 

 posteriorly, and using its parapodia for pushing food into its mouth. The 

 modern representative of this hypothetical crustacean-annelid, according to 

 Bernard, is Apus. In the Burgess shale (Middle Cambrian) crustacean 

 fauna of British Columbia occur certain annelids, like Canadia spinosa Walcott, 

 which have the head bent down so that the mouth faces posteriorly, and in 



1 Literature : Gerstaecker, A. and 0)-tmann, A. E., Crustacea, in Bronn's Klassen und Ordnungen 

 des Thierreichs, vol. v., 1866-1901.— Ca^maw, IT', T., Crustacea, in Lankester's Treatise on Zoology, 

 pt. vii., fasc. 3, 1909. 



- Walcott, C. D., Middle Cambrian Brauchiopoda, Malacostraca, Trilobita, and Merostomata. 

 Smithson. Misc. Coll., 1912, vol. Ivii., no. 6. 



