For example, since the exoskeleton is on the outside of the body, it limits growth. To grow, arthropods must undergo molting. In this process the animal steps out of its old skeleton and grows a new larger one. During the period of time in which a new skeleton is growing and hardening, the animal is vulnerable to being eaten by predators. The exoskeleton is also heavy, and this limits the size arthropods can become.
Arthropods inhabit almost all habitats.
There are aquatic arthropods living in both fresh water and marine environments. Some arthropods are terrestrial. Since the phylum is so highly diverse, most of the discussion below focuses on the crayfish. As a food source, the crayfish will eat almost anything. This type of animal is called an omnivore.