Introduction to Animal Morphology. 343 



CHAPTER XL. 



SUB-CLASS I. — CIRRIPEDIA {Burmeister). 



The Crustacea are mostly marine ; over 3000 species 

 are known as now living, divided into the following 

 sub-classes : — 



Sub-class I. Civrvpedia. [Bzirmeisfer] — retrogradely 

 metamorphosing Crustacea ; sessile in their adult con- 

 dition ; fixed by the front of the head. The dorso- 

 lateral integument is reduplicated around the body as a 

 mantle, and the pre-ovarian cement (antennary ?) gland 

 pours out a secretion through the third or disc joint of 

 the modified antennae, whereby the body is anchored.* 

 The hinder part of the body is free, lying in the 

 mantle cavity, and protrusible, retaining six pair 

 of prehensile, polyarthrous limbs, each with an endo- 

 and exopodite. The mantle becomes calcified and 

 chitinized in parts, forming a shell of several pieces, 

 united by intervening soft portions. The body may 

 be on a flat basis or stalked, the stalk or peduncle 

 being soft, horny, flexible, composed of the front of 

 the head, the cement ducts, and their secretion. The 

 feet (cirri) and soft part of the body periodically moult, 

 but the shell grows in successive layers, and is never 

 cast. 



The mouth lies in the mantle cavity, bordered by 

 a pair of toothed mandibles and a palp-bearing cly- 

 peus. The maxillae unite and form an under lip. The 



* In Lepas fascicularis the abundant cement forms a basis for the attach- 

 ment of a cluster of individuals, and may even form a float for them. 



