Tadpole Shrimp

Tadpole Shrimp, primitive freshwater crustacean. Tadpole shrimp are considered living fossils because their basic body characteristics have remained the same for millions of years. Tadpole shrimp are usually brownish in color and have a broad oval shield covering their anterior segments, making them look similar to miniature horseshoe crabs. Tadpole shrimp may reach a length of 2.5 cm (1 in). The presence of related fossil forms in Cambrian rock deposits shows these unique animals to be among the oldest of living crustaceans.

One species, the vernal pool tadpole shrimp, is found only in California. It inhabits temporary freshwater wetlands called vernal pools in the Central Valley. The vernal pool tadpole shrimp have adapted to a habitat that is watery during winter and spring and completely dry during the rest of the year. The vernal pool tadpole shrimp depend on the changing nature of the vernal pools in order to complete their life histories. The tadpole shrimp remain in eggs during the dry period and hatch as the pool fills with rainwater. During the wet season, they feed on fairy shrimp and other invertebrates, and lay their eggs. As the pools dry up, the adult shrimp die. Their limited distribution caused the vernal pool tadpole shrimp to be listed as endangered by the United States Fish and Wildlife Service in 1994.

Scientific classification: Tadpole shrimp are members of the order Notostraca, subclass Branchiopoda. The vernal pool tadpole shrimp is classified as Lepidurus packardi.