Nordman's Water Flea

Evadne nordmani

Microscopic and semitransparent. The body appears as a rounded triangle, and the head has a large eye. Four pairs of legs sit on the thorax, below the head. Adult females are 0.3 to 1.3 millimetres in length, males are 0.5 to 0.8 millimetres in length.

Authority

Lovén, 1836

Classification Details

Phylum: Arthropoda (arthropods); Subphylum: Crustacea (crustaceans); Superorder: Cladocera (water fleas).

Habitat

Planktonic. Common in both estuarine and coastal waters. Found worldwide, including in subpolar waters from Chesapeake Bay north. Occurs in salinities as low as one part per thousand. They prefer water temperatures less than 16°C.

Diet

Feeding appendages capture diatoms and dinoflagellates. May also eat ciliates and copepod larvae.

Reproduction

They go through a life cycle called cyclical parthenogenesis. For most of the year, females reproduce via parthenogenesis. This is a process that involves no males, and the eggs are not fertilized. They produce only females, and no males are in the population. Each female develops inside the mother and is born pregnant. When it is time for sexual reproduction, females produce both males and females that can mate. Fertilized eggs sink to the ocean floor, where conditions are better for hatching. Upon hatching, females emerge and begin producing more females.

Fun Facts

Their second antennae are used for propelling themselves through the water.

Because of their semitransparent bodies, you can see the embryos developing inside the mother, before they are born, and the eggs inside the embryos, inside the mother.

References

Johnson WS & Allen DM (2005) Zooplankton of the Atlantic and Gulf Coasts. Maryland: Johns Hopkins University Press.

World Register of Marine Species (2000) Evadne nordmanni Lovén, 1836 – WoRMS Taxon Details. http://marinespecies.org/aphia.php?p=taxdetails&id=106273 Accessed online 20 January 2020.

Van Guelpen L, Pohle G, Vanden Berghe E and Costello MJ (2005) Marine Species Registers for the North Atlantic Ocean. World Wide Web electronic publication. http://www.vliz.be/vmdcdata/narms/