Crustaceans have a full toolkit for feeding. On the front of a crustacean’s head are two pairs of sensitive antennae for feeling food. Picture a lobster’s long antennae swinging up and down. Two appendages, often claws, are used to seize food and break it up into pieces. Crustaceans typically have three pairs of biting mouthparts for chewing. The configuration of their mouthparts varies, depending on whether they are predators, scavengers, or filter feeders. While crustaceans have many adaptations for eating, they are also a common prey for other organisms. Humans eat millions of tons of crabs, lobsters, and shrimp every year. Tiny crustaceans, including krill and copepods, are part of the plankton that tend to congregate in the top few hundred meters of the ocean and are are vital to the marine food web. As krill and copepods feed, they concentrate ocean nutrients into their bodies, which then become available to the fish and filter-feeding organisms that prey on them.

Arthropods are the most successful group of organisms on Earth in terms of numbers, including almost half of all known species. The hallmark of their success is a body plan that makes them durable and adaptable. All arthropods have external skeletons made of hard material (chitin embedded in a protein matrix). The exoskeleton protects them from predators, weather conditions, and other threats. As they grow, arthropods typically shed the exoskeleton to reveal a bigger, fresh one underneath. The two lengthwise halves of an arthropod body are a mirror image of each other (bilateral symmetry) and typically divided into segments. Each segment has appendages that are specialized for the many activities of the arthropod. An arthropod may use appendages to feed (mouthparts), to breathe (gills, tracheae, book lungs), to reproduce (genitalia), and to move around (walking, swimming, flying). Having a modular body plan with multifunctional appendages has allowed arthropods to thrive in an impressive variety of environments.