ORIGIN AND RADIATION 



I I 



Darwin. The barnacle must be visualised as standing on its head, 

 attached by cement made in a gland which opens on the antennulc. 

 The abdomen is reduced to a vestige, and the carapace encloses the 

 whole body. The carapace of the cirripedes is usually called the 

 mantle, this is a term which dates from the time when barnacles 

 were thought to be molluscs. Various parts of the mantle are 

 thickened and have calcium salts deposited in them to form definite 

 plates. The number and arrangement of these plates are used to 

 distinguish the various families and genera of barnacles. 



CONCHODERMA 



/HO- 



'^^C CHTHftMALUS CH/lMfiESIPHO 



HI >s 



PLftM 

 CflTOPHRftCMUS 



BALANUS Et -MINI US PyP.COM 'A 



BAL£ N / C • . E 



Fig. ii. Diagram showing a possible evolutionary sequence of 

 some barnacles (Cirripedia) and the disposition of the plates. 

 C = carina; CL = carino-lateral; L = lateral; L(I) = inferior lateral; 

 L(S) = superior lateral; R = rostrum; RL = rostro-lateral; S = 

 scutum; T = tergum. In the plan of Catophragmus the scales on 

 the right side have been omitted. The scuta and terga have been 

 omitted from the other plans. 



It is thought that the regular arrangement of plates on the 

 mantle has evolved from a system of more numerous, less regular 

 plates. Pollicipes (fig. n) is a primitive genus, dating from the 

 Jurassic (150 million years ago), but still surviving to-day. A series 

 can be traced from Pollicipes, through Scalpellum to he pas, in 

 which the scales on the stalk are reduced and the plates on the 



