Cirripedia. 



31 



Sub-class IV.- CIRRIPEDIA. 



The members of this group are sedentary animals, attached by Table- 

 the anterior part of the head-region, and having the body generally ^os_^3&4. 

 enclosed by a fleshy mantle, representing the carapace, strength- 

 ened externally by shelly plates. There are typically six pairs of 

 trunk-limbs, each two-branched and many-jointed. 



On account of their shelly covering the Cirripedia were classed 

 by the older naturalists with the Mollusca, and it was only when 

 their larval stages were discovered in 1829 by J. Vaughan 



Fig. VI. 



Group of specimens of a stalked Barnacle (Lepas aiiatifera). One showing 

 the cirri extended as in life. [Table-case No. 3.J 



Thompson, that their affinities with other Crustacea were recog- 

 nised. Nearly all the Cirripedia are hermaphrodite, having both 

 sexes combined in each individual, a condition very rare among the 

 Arthropoda. In some cases, however, there are dwarf male 

 individuals which pair either with females or with hermaphrodites 

 of normal structure. 



The Sub-class may be divided into five Orders, but three of 

 these comprise only a few imperfectly-known forms which cannot 

 be exhibited here. 



