362 THE INVERTEBRATA 



as far as the 28th somite. Five limbless somites separate this from the 

 telson. The first thoracic limb is a modified phyllopodium, with the 

 endites slender and many-jointed, very long in Apus though shorter 

 in Lepidurus (Fig. 241). The second thoracic limb is less modified in 

 the same direction, the endites being shorter and unjointed. The re- 

 maining trunk limbs (Fig. 224) are normal phyllopodia: they decrease 

 in size from before backwards, and those of the thorax have the endites 

 well chitinized and mobile. Feeding is most often upon detritus (see 

 p. 355), the flat underside of the head being applied to the bottom 

 during the process, but the animals also devour the dead or living 

 bodies of organisms, clasping them with their strong thoracic limbs 

 and rasping fragments from them with the endites. The Notostraca 

 swim well, but can also crawl with their thoracic limbs or clamber 

 with the anterior pairs. 



The limbs of the genital somite are in the female modified for 

 carrying eggs, the flabellum fitting as a lid over a cup formed by the 

 distal part of the axis. Pvlales are rare, reproduction being normally 

 by parthenogenesis. 



Order DIPLOSTRACA 



Branchiopoda with a compressed carapace which usually encloses the 

 trunk and its limbs ; the compound eyes sessile and apposed or fused ; 

 the antennae large and biramous ; four to twenty-seven pairs of trunk 

 limbs, often considerably diflPerentiated ; and the telson usually ending 

 in a pair of curved claws. 



Suborder CONCHOSTRACA 



Diplostraca with 10-27 pairs of trunk limbs; the carapace provided 

 with adductor muscle in the maxillulary somite and with hinge, not 

 fused with thoracic somites, and usually enclosing the head; and 

 nearly always a Nauplius larva. 



No member of this order is British. 



The animals haunt the bottom and are mainly or exclusively 

 detritus feeders, dealing differently with fine and coarse particles 



(P-355)-. 



Estheria (Fig. 243) is a common European genus. A thoracic limb 



of a related but exotic form is shown in Fig. 222 C. 



Suborder CLADOCERA 



Diplostraca with 4-6 pairs of trunk limbs ; the carapace without hinge 

 or adductor muscle, fused with two or more thoracic somites, and 

 not covering the head ; and without Nauplius larva (save in Leptodora). 

 The members of this suborder are the water fleas. They fall into 

 four tribes. Of these, the first, known as Ctenopoda, show affinities 



