L * An independent anatomical investigation of the Mollusca had been carried on by the remarkable Neapolitan naturalist Poli (1791), whose researches 2 were not published until after his death (1817), and were followed by the beautiful works of another Neapolitan zoologist, the illustrious Delle Chiaje.3 The embranchement or sub-kingdom Mollusca, as defined by Cuvier, included the following classes of shellfish: (1) the cuttles or poulps, under the name Cephalopoda; (2) the snails, whelks and slugs, both terrestrial and marine, under the name Gastropoda; (3) the sea-butterflies or winged-snails, under the name Pteropoda; (4) the clams, mussels and oysters, under the name Acephala; (5) the lamp-shells, under the name Brachiopoda; (6) the seasquirts or ascidians, under the name Nuda; and (7) the barnacles and sea-acorns, under the name Cirrhopoda.
Vaughan Thompson, Zoological Researches (Cork, 1830); memoir iv., " On the Cirripedes or Barnacles, demonstrating their deceptive character."
Sometimes the one partner affords the other merely a convenient means of transport, as in the case of the barnacles which grow on, or of the gulf-weed crab which clings to, the carapace of marine turtles.
The barnacles and their allies, forming the group Cirripedia or Thyrostraca, sometimes treated as a separate sub-class, are distinguished by being sessile in the adult state, the larval antennules serving as organs of attachment, and the antennae being lost.
Originally, the name was given to the stalked barnacles (Lepadidae of C. Darwin), which attach themselves in great numbers to drift-wood and other objects floating in the sea and are one of the chief agents in the fouling of ships' bottoms during long voyages.