• Caption: Common Name: hydrozoan jellyfish, Scientific Name: Class Hydrozoa, Magnification: 5x, Notes: this is the free swimming lifestage, called a medusa, of a hydroid. It is not a true jellyfish although its form is very similar. Class Hydrozoa, Scientist's Notes: Can’t id. Very young hydromedusa., Location: Beneath the Golden Gate Bridge, San Francisco, California, Latitude: 37.82239565, Longitude: -122.48434066