CIRRIPEDIA 359 



snails, 'are unisexual, the male being a minute animal, consisting of little 

 but genital organs, which lives a parasitic life on the body of the female. 

 Cirripeds are born as nauplii and pass through a later larval stage pos- 

 sessing a bivalve shell, a pair of compound and a simple eye, called the 

 cypris stage, during which they attach themselves. 



History. The thick, calcareous shells of barnacles have always made 

 them conspicuous objects, and they have been well-known animals for a 

 very long time. The medieval zoologists supposed the Lepadidae to be 

 the young of bernicle geese, which often appear in large flocks along 

 the seashore of Europe, and this belief led them to call the animals goose 

 barnacles. It was not until the beginning of the eighteenth century 

 that this belief disappeared. The cirripeds were usually classified with 

 the mollusks by the earlier zoologists, although Lamarck in 1802 placed 

 them among the crustaceans, until J. V. Thompson in 1830 showed the 

 barnacle larva to be a nauplius and thus definitely proved their crus- 

 tacean nature. Cuvier, however, in 1830 still placed them among the 

 mollusks. 



About 500 species of Cirripedia are known, of which about 15 species 

 occur on our Atlantic coast. The order contains 5 suborders. 



Key to the suborders of Cirripedia here described : 



Ox Body enclosed in a calcareous shell ; barnacles 1. THOBACICA 



c 2 Body without a calcareous shell ; animals parasitic. 



Z>! Thoracic appendages present ; animals bore into the shells of mollusks 



and cirripeds 2. ABDOMINALIA 



6 2 Thoracic appendages wanting ; parasitic on decapods .... 3. RHIZOCEPHALA 



SUBORDER 1. THORACICA. 



Barnacles. Body enclosed in a calcareous shell and attached at the 

 dorsal side of the head, the 6 pairs of biramose, tendril-like thoracic legs 

 being thrust out as the shell opens to gather in the small animals and 

 organic fragments which form the food: about 4 families. 



Key to the families of Thoracica: 



Ox Body attached by a long, thick stalk. 

 Z>! Stalk almost or quite as wide as the rest of the body, and scaly. 



1. MlTELLIDAE 



6 2 Stalk much narrower than body 2. LEPADIDAE 



o 2 No stalk present. 



6 X On rocks, timbers, etc 3. BALANIDAE 



Z> 2 On whales 4. CORONULIDAE 



FAMILY 1. MlTELLIDAE. 



Stalk with scales or spines and as wide as the rest of the body, or 

 nearly so; shell consists of a large number (18 or more) of pieces; 

 mostly hermaphroditic, Scalpellum ornatum on the South African coast 



