The abdomen fits tightly beneath the cephalothorax. With the attachment of appendages, this gives the crab a unique appearance. Crabs can crawl forward slowly but commonly move in a sideways motion. This gives them a very comical appearance. Most crabs can not swim in the true sense but they are able to run at rapid rates.
Crabs exhibit a wide range of feeding habits such as herbivorous and scavenging tendencies.
Their food source is caught or picked up with the chelipeds or specialized front claws and then passed to the maxillipeds and into the mouth. The size and shape of the chelipeds reflects the feeding habits of the particular species of crab. Crabs, which have a diet of algae, have a spooned shaped claw. This allows them to scoop up or scrap algae off of the bottom or rocks. Those with a diet of shellfish have heavy claws with blunt teeth.