Crustacean Facts

Scientific Name: Crustacea

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

Crustaceans are some of the most important marine animals. Humans rely heavily on crustaceans for food; and crustaceans are also an important prey source for marine life in the ocean food chain for a variety of animals, including whales, fish, and pinnipeds.

More diverse than any group of arthropods, crustaceans are second or third in abundance of all categories of animal life after insects and vertebrates. They live in inland and ocean waters from the Arctic to the Antarctic as well as from elevations in the Himalayas up to 16,000 feet to well below sea level.

Fast Facts: Crustaceans

  • Scientific Name: Crustacea
  • Common Names: Crabs, lobsters, barnacles, and shrimp
  • Basic Animal Group: Invertebrate
  • Size: From 0.004 inches to over 12 feet (Japanese spider crab)
  • Weight: Up to 44 pounds (American lobster)
  • Lifespan: 1 to 10 years
  • Diet: Omnivore
  • Habitat: Throughout the oceans, in tropical to frigid waters; in freshwater streams, estuaries and in groundwater
  • Population: Unknown
  • Conservation Status: Many crustaceans are extinct, extinct in the wild, or endangered or critical. Most are classified as Least Concern.

Description

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. The largest crustacean is the Japanese spider crab, at over 12 feet long; the smallest are microscopic in size.

All crustaceans have a hard exoskeleton which protects the animal from predators and prevents water loss. However, exoskeletons don't grow as the animal inside them grows, so crustaceans are forced to molt as they grow larger. The molting process takes between a few minutes to several hours. 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. After molting, crustaceans typically expand their bodies almost immediately, increasing by 40 percent to 80 percent.

Many crustaceans, such as the 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 (the mouth parts 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.

Lady Elliot Island
Rowan Coe/Getty Images

Species

Crustaceans are a subphylum of the Arthropoda phylum in the Animalia. According to the World Register of Marine Species (WoRMS), there are seven classes of crustaceans:

  • Branchiopoda (branchiopods)
  • Cephalocarida (horseshoe shrimp)
  • Malacostraca (decapods—crabs, lobsters, and shrimps)
  • Maxillopoda (copepods and barnacles)
  • Ostracoda (seed shrimp)
  • Remipedia (remipedes)
  • Pentastomida (tongue worms)

Habitat and Range

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 a small lobster hiding. You might also find some small shrimp paddling around. 

Crustaceans live in freshwater plankton and benthic (bottom-dwelling) habitats, and can also be found residing in groundwater near rivers and in caves. In temperate locations, small streams support some crayfish and shrimp species. Species richness in inland waters is highest in fresh water, but there are species that live in salt and hypersaline environments.  

To protect themselves from predators, some crustaceans are night hunters; others stay in protected shallow slack-water locations. Rare and geographically isolated species are found in karst caverns which get little if any light from the surface. As a result some of those species are blind and unpigmented. 

Diet and Behavior

Within the literally thousands of species, there is a wide variety of feeding techniques among crustaceans. Crustaceans are omnivores, although some species eat algae and others like crabs and lobsters are predators and scavengers of other animals, feeding on those that are already dead. Some, like barnacles, remain in place and filter plankton from the water. Some crustaceans eat their own species, newly molted individuals, and young or injured members. Some even change their diets as they mature.

Reproduction and Offspring

Crustaceans are primarily dioecious—made up of male and female sexes—and therefore reproduce sexually. However, there are sporadic species among the ostracods and brachiopods that reproduce by gonochorism, a process by which each individual animal has one of two sexes; or by hermaphroditism, in which each animal has complete sex organs for both male and female sexes; or by parthenogenesis, in which the offspring develop from unfertilized eggs.

In general, crustaceans are polyandrous—mating more than once in the same breeding season—and are fertilized within the female. Some may begin the gestation process immediately. Other crustaceans such as crayfish store the spermatozoa for many months before the eggs are fertilized and allowed to develop.

Depending on the species, crustaceans disperse eggs directly into the water column, or they carry the eggs in a pouch. Some carry the eggs in a long string and attach the strings to rocks and other objects where they grow and develop. Crustacean larvae also vary in shape and development process by species, some going through multiple changes before reaching adulthood. Copepod larvae are known as nauplii, and they swim using their antennae. Crab crab larvae are zoea which swim using thoracic appendages. 

Conservation Status

Many crustaceans are on the International Union for Conservation of Nature Red List as vulnerable, endangered or extinct in the wild. Most are classified as Least Concern. 

Sources

  • Coulombe, Deborah A. "The Seaside Naturalist." New York: Simon & Schuster, 1984.
  • 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.
  • Thorp, James H., D. Christopher Rogers, and Alan P. Covich. "Chapter 27 - Introduction to “Crustacea." Thorp and Covich's Freshwater Invertebrates (Fourth Edition). Eds. Thorp, James H. and D. Christopher Rogers. Boston: Academic Press, 2015. 671–86.
  • WoRMS. 2011. Crustacea. World Register of Marine Species.