Crustacean Characteristics and Other Basic Facts

Learn About Their Important Role in Marine Life

Red rock crab (Grapsus grapsus), a type of crustacean
Red rock crab (Grapsus grapsus), a type of crustacean. Juergen Ritterbach/Digital Vision/Getty Images

If you think just in terms of your stomach, crustaceans are some of the most important marine animals. Humans rely heavily on crustaceans for food. They are, of course, an important prey source for marine life in the ocean food chain as a prey source for a variety of animals, including whales, fish, and pinnipeds.

What Are Crustaceans?

Crustaceans include commonly-known marine life such as crabs, lobsters, barnacles, and shrimp. These animals are in the Phylum Arthropoda (the same phylum as insects) and Subphylum Crustacea. According to the Natural History Museum of Los Angeles County, there are over 52,000 species of crustaceans.

Characteristics of Crustaceans

All crustaceans have a hard exoskeleton, which protects the animal from predators and prevents water loss. However, exoskeletons can't grow as the animal inside them grows, so crustaceans are forced to molt as they grow larger. During molting, a soft exoskeleton forms underneath the old one and the old exoskeleton is shed. Since the new exoskeleton is soft, this is a vulnerable time for the crustacean until the new exoskeleton hardens.

Many crustaceans, such as American lobster have a distinct head, a thorax, and an abdomen. However, these body parts aren't distinct in some crustaceans, such as the barnacle. Crustaceans have gills for breathing.

Crustaceans have two pairs of antennae. They have mouths made up of one pair of mandibles (which are eating appendages behind the crustacean's antennae) and two pairs of maxillae (mouthparts located after the mandibles).

Most crustaceans are free-ranging, like lobsters and crabs, and some even migrate long distances. But some, like barnacles, are sessile—they live attached to a hard substrate most of their lives.

Crustacean Classification

  • Kingdom: Animalia
  • Phylum: Arthropoda
  • Subphylum: Crustacea
  • Classes: (According to the World Register of Marine Species (WoRMS):
    • Branchiopoda (branchiopods)
    • Cephalocarida (horseshoe shrimp)
    • Malacostraca (the class that includes decapods—crabs, lobsters, and shrimps)
    • Maxillopoda (which includes copepods and barnacles)
    • Ostracoda (seed shrimp)
    • Remipedia (remipedes)
    • Pentastomida (tongue worms).

Where to Find Crustaceans

If you're looking for crustaceans to eat, look no further than your local grocery store or fish market. But seeing them in the wild is almost as easy. If you'd like to see a wild marine crustacean, visit your local beach or tide pool and look carefully under rocks or seaweed, where you might find a crab or even small lobster hiding. You might also find some small shrimp paddling around. 

In a broader sense, marine crustaceans can be found throughout the oceans, in tropical to frigid waters. Have you seen the cold weather inhabited by the king and snow crabs featured on Deadliest Catch?

How Do Crustaceans Feed and What Do They Eat?

With thousands of species, there is a wide variety of feeding techniques among crustaceans. Some, like crabs and lobsters, are active predators, some are scavengers, feeding on animals that are already dead. And some, like barnacles, remain in place and filter plankton from the water.

How Do Crustaceans Reproduce?

Most crustaceans are dioecious, meaning individuals are male or female. Reproduction varies among species.

Examples of Crustaceans

Here are some examples of crustaceans:

  • Acadian Hermit Crab
  • American Lobster
  • Copepod
  • Ghost Crab
  • Hawaiian Brown Slipper Lobster
  • Pillbugs
  • Sally Lightfoot Crab
  • Skeleton Shrimp
  • Spider Crab
  • Krill


Coulombe, Deborah A. 1984. The Seaside Naturalist. Simon & Schuster.

Martinez, Andrew J. 2003. Marine Life of the North Atlantic. Aqua Quest Publications, Inc.: New York

Myers, P. 2001. "Crustacea" (On-line), Animal Diversity Web.

WoRMS. 2011. Crustacea. World Register of Marine Species.