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Chrysaora melanaster Marrus orthocana
True jelly-fish

Colonial jellies


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Cnidarians - Jellyfish & Kin

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Cnidarians get their name from the “stinging nettle” cells that are unique to this group. This is the most priamtive group of multi-celluar zooplankton, basically two layers of skin with jelly in between them. They are also characterized by a radial symmetry only found in a few other phyla.

The group contains the true jellyfish, the hydromedusae which look very similar to jellyfish but are usually smaller, plus a colonial subgroup, the siphonophores, that contains animals like the Portuguese-man-o-war. Some species have powerful stinging cells that cause pain, and even death in humans. With few exceptions, the group is predatory and capable of eating any plankton or fish they can catch. Some species carry symbiotic algae in their tissue that produce part of the energy needed by the animal, very similar to what their cousins the corals do.

Within the water column they can be common, frequently being a large but variable proportion of the volume of zooplankton collected by nets. Some species have relatively few predators, while others are preyed on heavily by other cnidarians, and fish such as mackerel and chum salmon.

There are ~70 species of cnidarians with prominent planktonic phases known to exist in the arctic.

Page Author: Russ Hopcroft
Revised: Aug 20, 2010

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