Crayfish also known as craw fish are the freshwater crustaceans. If we talk about their structure, crayfish have an adjustable eyes that can moves around in all directions, thus helping them to sense danger. Apart from this, they have antennae which helps them to discover the movements in the water.
Similarly, every living creature on this planet have varied forms of structures which allow them to be successful in their environment. Those structure could be anything- it could be either their powerful sense of smell or their sharp long teeth, it could be their powerful body or anything.