Most crabs are omnivorous. Some crabs are carnivorous. For example, Portunus can prey on fish, shrimp and mollusks. A few crabs, such as window crabs, scrape or filter algae and organic debris.
Somatotype characteristics
Crab's body is divided into head, chest and abdomen. The head, chest and back are covered with head and breastplate, and the shape varies from species to species. There are 1 and 2 pairs of antennae in the center of the forehead, and compound eyes with stalks on the outside. The mouthparts include 1 pair of big jaws, 2 pairs of small jaws and 3 pairs of jaws.
There are five pairs of chest feet on both sides of the head breastplate. The abdomen degenerates, flattens and bends on the ventral surface of the head and chest. The male abdomen is long and narrow, mostly triangular, and only the first two pairs of appendages are deformed into connectors; The female has a broad abdomen, and there are 1 pairs of double-branched appendages in the 2nd to 5th sections, which are densely covered with bristles for holding eggs. Most crabs are marine, with the most species in tropical shallow waters.