1. Appearance: the sea rainbow is a mollusk with a long cylindrical body, usually with a red, yellow or brown shell, while the crab has an exoskeleton similar to a carapace, usually oval or quasi-round.

2. Posture: The sea rainbow crawls slowly in the sea, which is usually considered as a state without posture, while crabs can move on the seabed or on the beach. They can walk, climb mountains, practice or swim.

3. Living habits: Haihong usually lives at the bottom of the ocean, is a carnivorous animal and feeds on small invertebrates, while crabs can live in the ocean, fresh water or land. They are omnivores and can eat plants and animals.