There are a few Crustacea living habitually on the high seas which cannot be reckoned as belonging either to the true plankton or to the necton, since they depend on outside help for keeping themselves afloat. Among these are the Barnacles which cluster on logs of drift-wood, and are among the most important causes of the "fouling" of ships' hulls on long voyages. The stalked Barnacles of the genus Lepas are especially common in such situations, and the characters of their larvæ have been already alluded to. Certain species of sessile Barnacles are constantly found attached to large marine animals. For example, Chelonobia adheres to the shell of Turtles, while Coronula and some allied genera are found on Whales.
PLATE XIX
Latreillia elegans, ONE OF THE DROMIACEA WHICH RESEMBLES A SPIDER-CRAB. FROM THE MEDITERRANEAN. (NATURAL SIZE)
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THE GULF-WEED CRAB, Planes minutus. (SLIGHTLY ENLARGED)
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