Gonionemus

Gonionemus vertens A. Agassiz, 1862 
Phylum Cnidaria / Class Hydrozoa / Order Limnomedusae / Family Olindiasidae
Hydromedusa, Gonionemus vertens, Monterey Bay, Pacific Ocean

Here’s a jelly that doesn’t like to swim. Using adhesive discs near the middle of each tentacle (visible as light spots on the tentacles in the photo), Gonionemus attaches to eelgrass, sea lettuce or various types of algae. They are small (bell diameter to 25 mm) and hard to find when hanging on to swaying seaweeds. Although typically attached to something, they are capable of swimming when necessary. The bell is transparent, revealing the 4 orange to yellowish-tan gonads that lie along most of the length of the 4 radial canals. The pale yellow manubrium has 4 short frilly lips. Up to 80 tentacles line the bell margin, with about an equal number of statocysts. Copepods are a favored prey. Whereas Pacific Northwest Gonionemus vertens lacks a sting that is felt by people, the same species in the Russian Far-East is known to be venomous. This nearshore limnomedusa inhabits quiet waters of northern Japan and Kamchatka (Russia), and from Alaska’s Aleutian Islands to northern California.

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