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Not much is known regarding the food of deep-sea animals. In the absence of plant-life they must of necessity be all carnivorous, and all ultimately dependent on the food-supply falling from above. Some species have been found to have the food-canal filled with Globigerina ooze, which they no doubt swallow, as earth-worms do the soil in which they burrow, for the purpose of extracting the nutriment that it contains. In one species of deep-sea Cumacea (Platycuma holti), which appears to feed in this manner, the food-canal is coiled, a condition very rare in Crustacea; in all probability this is due to the necessity for an increase of the absorptive surface, since it is common to find such an increase, either by lengthening and consequent coiling of the gut, or by infolding of its walls, in animals that have to swallow large quantities of relatively innutritious food material. Many species, however, no doubt have more selective habits of feeding. The lobster-like Thaumastocheles ([Fig. 44]), which was dredged by the Challenger expedition in the West Indies at a depth of 450 fathoms, and has since been got from deep water off the Japanese coast, has one of the chelæ enormously enlarged, with long and slender fingers set with spines like the teeth of a rake. It has been suggested that this remarkable claw may be used for raking or sifting the ooze for small animals on which the Thaumastocheles feeds. A similar function may be suggested for the long and spiny first pair of walking legs in the Spider Crab Platymaia ([Fig. 45]).

Fig. 44—Thaumastocheles zaleucus. Reduced. (After Spence Bate.)

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Fig. 45—A Deep-sea Crab (Platymaia wyville-thomsoni). Reduced.

(After Miers.)