The members of the tribe Hippidea (sometimes called "Mole Crabs"), among the Anomura, have habits somewhat similar to those of the Crabs just described. They are common on sandy beaches in the warmer parts of the globe, and they burrow with great rapidity by means of the curved, flattened end-segments of the legs. The carapace is generally smooth and oval, and the body is compact, the short abdomen being folded up as in the Crabs.

In Albunea ([Plate XIV].), which belongs to this tribe, a long "antennal tube," which looks very like that of Corystes, is believed to have a similar function in connection with respiration when the animal is buried. In this case, however, the tube is formed, not by the antennæ, as in Corystes, but by the antennules, so that it affords a striking example of the independent evolution of similar structures from quite different origins.

Hippa emerita, which is found on the coasts of North and South America, has the mouth parts imperfectly formed, and not adapted for biting; and it is stated by Professor S. I. Smith that the animal feeds in the way that an earthworm does, swallowing the sand through which it burrows, and extracting the nutriment which it may contain. This habit, however, is not followed by other members of the tribe, for Mr. Borradaile found that a species of Remipes in the Maldive Islands could "easily be caught by a bait of Crab at the end of a line, pouncing on it with its sharp maxillipeds, and allowing itself to be flicked out of the sand if the rod be sharply lifted."

In the cases mentioned above, the Crustacea do not bury themselves much below the surface of the sand, and do not form definite burrows; but there are many Crustacea which live in open tunnels dug deep into the sand. Some of these belong to the category of amphibious forms, to be mentioned presently; but there are others which live in deeper water, and of which the habits are less open to observation.

Fig. 38—Callianassa stebbingi (Female), a Sand-burrowing Thalassinid from the South Coast of England. Natural Size

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Nearly all the Thalassinidea ([Fig. 38]) live in burrows, often of considerable depth, in sand or mud. Although now classed with the Anomura, these animals are lobster-like in form, loosely built, generally with short carapace and long, soft abdomen. They have usually very small eyes, which appear as if they were not of much use for vision; and some of the hinder pairs of legs are short, and carried folded against the sides of the body, probably for use when the animal is moving up or down in its burrow.