PHYLUM ARTHROPODA 



581 



The eyes (a) are large, compound, and raised on movably articu- 

 lated stalks. The antennules (04) and antennae ( 2 ) are large, the 

 mandibles (md.) have palps 

 (m), and the exopodite of 

 the second maxilla (mxt) has 

 the form of a slender filament 

 which acts as a "cleaning- 

 foot " to keep the cavity of 

 the carapace free from foreign 

 bodies. There are eight thor- 

 acic appendages (/>?/), all of 

 them leaf-like, and recalling 

 those of Apus. The first 

 four abdominal appendages 

 (l>/ p4) are large biramous 

 swimming-feet, like those of 

 Copepods ; the fifth and sixth 

 (p~>, 2^6) are small and uni- 

 ramous. 



The Syncarida (Anaspid- 

 '",'/) (Fig. 458) are small, 

 shrimp-like, fresh -water Crus- 

 taceans, which, though re- 

 sembling the rest of the 

 Malacostraca (Eumalacos- 

 traca) in the presence of only 

 six segments in the abdomen 

 and the absence of caudal 

 styles, differ from them in 

 the possession of a combina- 

 tion of features which con- 

 nect them more closely with 

 certain fossil forms of Car- 

 boniferous age. Thus there 

 is no carapace, the thoracic 

 appendages are provided with 

 slender respiratory exopo- 

 dites, and bear a double 

 series of epipodites or bran- 

 chiae ; there are stalked eyes 

 and a fan-like tail-fin formed 

 of the telson and the ex- 

 panded uropods. 



The Mysidacca (Fig. 459) 



are small, transparent, shrimp-like forms, mostly from 2 6 mm. 

 in length. They agree with the Crayfish in the general form 

 of the body, in the union of the head and thorax, in the 



FIG. 457. Webalia geoffroyi. male, a. eye ; 

 1, antemiule ; a%, antenna ; c, head ; brf. thoracic 

 feet; d, intestine; /*.. heart; Im, gizzard; md. 

 mandible ; mt, mandibular palp ; mnt. exo- 

 podite of second maxilla ; p^ p, pleopods ; 

 r. rostrum ; , carapace ; sm, adductor muscle ; 

 t. testis ; / yjll, thoracic segments. (From 

 Lang's Comjtarativs Anatomy, after Glaus.) 



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