Swimmer Crabs have flattened, paddle-like rear legs used for swimming or burrowing in the sand. Most species are nocturnal predators of molluscs, crustaceans and occasional fishes, and live on the bottom. Some, which attain a large size, are renowned for their edibility; in fact the family includes most of the crabs sold in markets and restaurants. Swimmers are classified as true crabs (brachyarans) as the first pair of legs are clawed and the last pair are not much smaller than the others. In addition, the antennae are very short. A conspicuous feature that separates them from the other major group of crabs (the anomurans) is the shape of the abdomen very short, flat, and folded under the body. In contrast, many anomurans have a lobster-like abdomen, although some species hold it under the body as do the true crabs. All crabs lay huge number of eggs, which are carried on the paired appendages (pleopods) between the thorax and the abdomen.
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