This is a moon jelly, Aurelia aurita. These jellies are quite common along the Atlantic coast of the United States and the Bahamas. The medusa form, shown here, predominates in the jelly life cycle. As members of the phylum Cnidaria, jellies have only two layers of tissue, which are separated by an acellular layer called the mesoglea. The gelatinous consistency of the mesoglea gives jellies their name. The tentacles you can see hanging downward contain nematocysts, stinging cells that can be discharged upon contact with another organism. Toxins in the nematocysts can paralyze the prey, so that they can be ingested through the jelly's centrally located mouth and then digested in its baglike gastrovascular cavity. The four white rings in the center of the bell are the gonads, where the gametes will form. Jellies can reproduce either asexually by budding, or sexually. Credit: National Geographic.