Arctic Hydromedusa

Hydromedusae form the largest group of cnidarians and are generally smaller then the true jellyfish (typically only a few millimeters to centimenters at maximum size). Hydromedusae are distinquished from true jellyfish by prodcing their eggs and sperm under the bell, but on the outside of the animal, while true jellyfish produce eggs inside the gut.

Cnidarians can be found all the way from the surface to the bottom of the oceans, although most species have a specific range of depth over which they are found. Within the water column, hydromedusae they can be common, frequently being a large but variable proportion of the volume of zooplankton collected by nets. All Hydromedusae are predatory and eat smaller zooplankton. Some species have relatively few predators, while others are preyed on heavily by other cnidarians, and fish such as mackerel and chum salmon.