Kingdom - Animalia

Phylum - Arthropoda

Subphylum - Crustacea


Crustaceans have:

  • hard exoskeleton.
  • segmented bodies.
  • jointed limbs.
  • biramous (branching) appendages.
  • larval stage.
  • five-segmented head (cephalon).
  • two pairs of antennae.




Basic Crustacean Taxonomy

There are 6 classes:


  • 40,000 species on earth
  • abdominal appendages
  • three tagmata
1. five-segmented head
2. eight-segmented thorax
3. six-segmented abdomen with telson

In Illinois there are 71 known species:aquaticsowbug.png

Amphipoda - scuds - 19 species

Isopoda - pillbugs - 28 species

Decapoda - crayfish and shrimp - 23 species

Mysidacea - opossum shrimp - 1 species

Maxillopoda - barnacles, copepodscopepod.png

  • five-segmented head
  • six-segmented thorax
  • four abdominal segments with a telson
  • feed with maxillae (mouthparts) rather than filter feed

In Illinois there are 31 known species:

Branchiura - fish lice - 10 species

Copepoda - copepods - 21 species



  • 30 extant species
  • marine crustacea
  • no known members in Illinois
  • closest Crustacea relatives of the insects

Ostracoda - seed shrimpostracod.png

  • 70,000 species on earth
  • body is not clearly segmented
  • no gills
  • no circulatory system
  • body is flattened from side to side
  • hinged "shell" made of chitin

 In Illinois there are 53 species:







  • 800 species on earth
  • freshwater
  • have gills on their appendages

In Illinois there are 52 known species:

Anostraca - fairy shrimp - 4 species

Conchostraca - clam shrimps - 5 species

Diplostraca - water fleas - 43 species


Cephalocarida - horseshoe shrimps

  • 12 extant species
  • benthic marine crustacea
  • no known members in Illinois


Crustaceans are invertebrate animals in the phylum Arthropoda, subphylum Crustacea, and include the barnacle, crab, crayfish, lobster, shrimp, water flea, and pill bug. Although largely aquatic, a few crustaceans are found in terrestrial habitats. Of the nearly 67,000 aquatic species of crustaceans, only about 10% occur in freshwater habitats. Crustaceans have evolved a variety of specialized body forms and behaviors to cope with both aquatic and terrestrial environments, however, all crustaceans share several characteristics: a hard exoskeleton; jointed, paired appendages; and three body regions (head, thorax, and abdomen). The head and thorax regions are sometimes combined into a cephalothorax.

The smallest arthropod in the world is a 0.1 millimeter crustacean Stygotantulus stocki. The Japanese spider crab is the largest arthropod with a leg span of 3.8m! Biologists continue to discover new species from around the world. These biologists are also investigating the phylogenetic relationships, ecology, behavior, and physiology of crustaceans. Several crustaceans of great economic importance, such as lobsters and shrimps, are also examined from a managerial perspective.


INHS Crustacean Collection and other links about Crustacea


Some past articles published in INHS Reports:

Species Spotlight: Terrestrial Isopods. Summer 2000

New Predator Invades the Great Lakes: Cercopagis pengoi. May-June 2000

INHS Crustacean Collection. March-April 1999

Status and Distribution of Daphnia lumholtzi Sars in Illinois . November-December 1998

The Rusty Crayfish in Illinois. November-December 1998

Introduced Crayfishes in Illinois. January-February 1996