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Gonionemus vertens
Image courtesy of Dave Cowles at
Gonionemus vertens
Taxonomic Group: Cnidarians-Hydrozoans


The hydroid Gonionemus vertens, commonly known as the Clinging Jellyfish, has a small, solitary polyp stage, but a conspicuous medusa stage. It is native to the North Pacific, from Vietnam to the Sea of Okhotsk in the Western Pacific, and Puget Sound to the Aleutian Islands in the Eastern Pacific. Introduced populations have been reported from Southern California, Massachusetts, Connecticut, Europe and the Mediterranean Sea. The tiny polyp stage occurs among benthic debris and algae on rocks, shells, and vegetation. The medusa stage is often found clinging to eelgrass or other vegetation during the day and swimming in the water column at night. It has a potent sting and can cause muscle cramps, chest tightness and swollen throats in people who are stung. This jellyfish is not likely to be abundant in areas heavily used by swimmers, but could affect casual waders and people gathering shellfish near eelgrass beds.

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Fofonoff PW, Ruiz GM, Steves B, Simkanin C, & Carlton JT. .
National Exotic Marine and Estuarine Species Information System.
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Marine Invasions Lab
Smithsonian Environmental Research Center

P.O. Box 28
647 Contees Wharf Road
Edgewater, MD 21037-0028 Tel: 443 482 2200
Fax: 443 482 2380

Cal-NEMO Database |