He upset (1830) Cuvier's retention of the Cirripedes among Mollusca, and his subsequent treatment of them as an isolated class, by showing that they begin life as free-swimming Crustacea identical with the young forms of other Crustacea.
Under the heading Crustacea the Entomostraca have already been distinguished not only from the Thyrostraca or Cirripedes, but also from the Malacostraca, and an intermediate group of which the true position is still disputed.
Vaughan Thompson, Zoological Researches (Cork, 1830); memoir iv., " On the Cirripedes or Barnacles, demonstrating their deceptive character."
These, with Darwin's three families above mentioned, complete the section of genuine cirripedes now existing.
The vernacular name barnacle, traceable to the fable of pedunculate cirripedes hatching out into bernicle geese, has also been transferred to the sessile cirripedes, which are popularly known as acorn barnacles.
It is generally stated that cirripedes are confined to salt water, and, generally speaking, that is true.