Freshwater hydroid

Scientific Name: Cordylophora caspia


Nadine RoremCopyright Info


Nadine RoremCopyright Info

Identification: A freshwater hydroid is a simple, soft-bodied animal related to corals and jellyfish. This non-native species is elongated and vase-shaped with a ring of tentacles surrounding its mouth. It forms branching colonies that have a moss-like appearance.


Size: Colonies of this species grow up to 2 inches (5 cm) tall. Individuals are less than 0.06 inch (1 mm) tall.


Native Range: This hydroid is native to the Black and Caspian seas, which are bordered by Eastern Europe and the Middle East.


Table 1. Great Lakes region nonindigenous occurrences, the earliest and latest observations in each state/province, and the tally and names of HUCs with observations†. Names and dates are hyperlinked to their relevant specimen records. The list of references for all nonindigenous occurrences of Cordylophora caspia are found here.

Full list of USGS occurrences

State/ProvinceYear of earliest observationYear of last observationTotal HUCs with observations†HUCs with observations†
Illinois200720071Lake Michigan
Minnesota200120011St. Louis
New York200720071Seneca
Ohio195619561Ashtabula-Chagrin

Table last updated 5/25/2018

† Populations may not be currently present.


Means of Introduction: This non-native hydroid was probably introduced into Lake Erie with its release from personal aquaria. Transoceanic ship water discharges appear to have introduced the species to Washington coastal waters.


Status: This freshwater hydroid has been found in Lake Erie, southern Lake Michigan, and the Duluth-Superior Harbor, as well as the coastal waters of California, Florida, and Washington. This species has also been found in the Illinois, Hudson, and Connecticut rivers.


Remarks: This freshwater hydroid may benefit from the presence of zebra mussels (Dreissena polymorpha) and quagga mussels (Dreissena bugensis), which are native to the same area and are also in the Great Lakes. This species may compete with zebra mussels for surfaces to colonize. However, once a mussel colony is established, this hydroid can attach to and colonize the surface of mussel shells. This freshwater hydroid also typically eats the larval forms of zebra and quagga mussels.


Author: Illinois-Indiana Sea Grant


Contributing Agencies:
NOAA Sea Grant GLRI Logo


Revision Date: 9/25/2012


Citation for this information:
Illinois-Indiana Sea Grant, 2019, Freshwater hydroid: U.S. Geological Survey, Nonindigenous Aquatic Species Database, Gainesville, FL, and NOAA Great Lakes Aquatic Nonindigenous Species Information System, Ann Arbor, MI, https://nas.er.usgs.gov/queries/greatLakes/FactSheet.aspx?SpeciesID=1060&Potential=N&Type=1&HUCNumber=DGreatLakes, Revision Date: 9/25/2012, Access Date: 3/18/2019

This information is preliminary or provisional and is subject to revision. It is being provided to meet the need for timely best science. The information has not received final approval by the U.S. Geological Survey (USGS) and is provided on the condition that neither the USGS nor the U.S. Government shall be held liable for any damages resulting from the authorized or unauthorized use of the information.