552 ZOOLOGY SECT. 



ORDER 2. RHIZOCEPHALA. 



Parasitic Cirripedia in which the body has undergone extreme 

 degeneration, and has lost all trace of appendages and of ali- 

 mentary canal in the adult condition. 



Including Sacculina (Fig. 463) and PeUogaster. 



Sub-class V. Malacostraca. 



Crustacea in which the body is always distinctly segmented and 

 is made up in all cases except the Leptostraca of an anterior region 

 (thorax) of eight segments, and a posterior (abdomen) of six, with a 

 terminal tail-piece or telson the total number of segments, 

 leaving the prostomium and the telson out of account, being always 

 nineteen. The appendages of the thorax and abdomen are sharply 

 marked off from one another. The abdomen is devoid of caudal 

 styles. The exoskeleton of the head united with that of more or 

 fewer of the thoracic segments to form a cephalothoracic carapace. 

 Paired eyes are usually present and may be sessile or stalked. 

 The antennules are biramous in most cases. The mandibles are 

 provided with a palp. There is usually a metamorphosis, but a 

 nauplius-stage rarely occurs. 



Series I. Leptostraca (Phyllocarida). 



Malacostraca in which the abdomen contains seven segments 

 and a telson the last segment devoid of appendages, the telson 

 bearing a pair of caudal styles. There is a large bivalved carapace 

 with an adductor muscle, enclosing the greater part of the body. 

 The thoracic appendages are foliaceous, the abdominal biramous. 



Includes only one order, the Nebaliacea, with Nebalia (Fig. 464) 

 and three allied genera. 



Series II. Eumalacostraca. 



Malacostraca with six segments and a telson in the abdomen, 

 the latter never provided with caudal styles. Carapace never 

 bivalve. Thoracic appendages nearly always leg-like, but seldom 

 all uniform : their protopodite always made up of two podomeres 

 except in the Stomatopoda. 



Division 1. Syncarida. 



Eumalacostraca devoid of carapace, with the first thoracic 

 segment united with the head or marked off from it by a groove. 

 Heart elongated, tubular. 



ORDER ANASPIDACEA. 



Syncarida in which the thoracic appendages are provided (except 

 the last or the last two) with exopodites, and (except the last) 

 with a double series of lamellar epipodites (gills). The abdominal 



