any of a widely distributed group of crustaceans resembling mussels. Mussel shrimp differ from most crustaceans in having a very short trunk that has lost its external segmentation, or divisions. Nearly all of the body is encased in a hard covering, or carapace. The 2,000 living species include marine, freshwater, and terrestrial forms
Learn more about ostracod with a free trial on Britannica.com.