The true crabs (Cancer, carcinus, Portumis, etc.) reach the highest degree of specialization among Crustacca. The cephalothorax is baroader than longer. Both the pairs of feelers are small. The antennules and the eye stalks are contained in sockets of the carapace. The third maxillipedes are flat and plate-like and cover the other mouth parts. The five pairs of thoracic legs are well-developed and clawed. The first legs are chelate, forming the large pinching claws, the remaining legs are non-chelate.The abdomen is very short with an uncalcified, soft sternal region. It is permanently bent under the cephalothorax, fitting into a groove in the thoracic sterna, thus remaining almost invisible in the dorsal view of the animal. The abdomen is narrower in male but somewhat broader in female. The pleopods are greatly reduced, the male retaining only two pairs of them, which serve as copulatory organs ; the female has four pairs for carrying the eggs. The uropods are usually absent. The young hatches in the zoaea stage, which passes through a megalopa stage before reaching maturity.
The true crabs (Cancer, carcinus, Portumis, etc.) reach the highest degree of specialization among Crustacca. The cephalothorax is baroader than longer. Both the pairs of feelers are small. The antennules and the eye stalks are contained in sockets of the carapace. The third maxillipedes are flat and plate-like and cover the other mouth parts. The five pairs of thoracic legs are well-developed and clawed. The first legs are chelate, forming the large pinching claws, the remaining legs are non-chelate.The abdomen is very short with an uncalcified, soft sternal region. It is permanently bent under the cephalothorax, fitting into a groove in the thoracic sterna, thus remaining almost invisible in the dorsal view of the animal. The abdomen is narrower in male but somewhat broader in female. The pleopods are greatly reduced, the male retaining only two pairs of them, which serve as copulatory organs ; the female has four pairs for carrying the eggs. The uropods are usually absent. The young hatches in the zoaea stage, which passes through a megalopa stage before reaching maturity.
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