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 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. 12. 
Group of specimens of a stalked Barnacle ( Lepas anatifera). One showing 
the cirri extended as in life. [Table-case No. 3.] 
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-ciass may be divided into five Orders, but three of 
these comprise only a few imperfectly-known forms which cannot 
be exhibited here. 
