386 THE INVERTEBRATA 



Gerardia, has the mantle in the form of a very spacious sac with a 

 narrow opening. Its abdomen has two somites and a telson, 



Syiiagoga (Fig. 263), external parasite on Antipathes, has a bivalve 

 mantle, from which usually protrudes the long abdomen of four 

 somites and a telson. It is possible that this is an immature stage 

 of an animal which is more retrograde when it is adult. 



Fig. 262. 



Fig. 263. 



Fig. 262. An abdominal limb of the prawn Synalpheus infested by Tho?np- 

 sonia, x 120. From Potts, bl. blind branch of root system which after further 

 development will become an external sac; en. endopodite of limb of host; 

 ex. exopodite of the same; mtl. mantle of sac; stk. stalk; vm. visceral mass, 

 occupied entirely by the ovary. 



Fig. 263. Synagoga mira. After Norman, ab.i, first abdominal somite; ait.' 

 antennule ; car. mantle (carapace) ; M. mouth ; ram. ramus of caudal fork ; 

 tel. telson ; th. thoracic limbs. 



Class MALACOSTRACA 



Crustacea with compound eyes, which in typical members of the 

 group are stalked ; typically a carapace which covers the thorax ; the 

 mandibular palp, if present, uniramous ; a thorax of eight somites and 

 abdomen of six (rarely seven), all (except the 7th abdominal) bearing 

 appendages; and a complex proventriculus. 



The Malacostraca contain a very large number of species, which 

 exhibit great diversity. Nevertheless they are capable of reference to 

 a common type in respect of more features than the members of any 



