Scyphozoa
- Members o the class scyphozoa are all marine and are "true jellyfish" because their dominant stage in their life history is the medusa
- Unlike hydrozoan medusae, scypjozoan medusae lack a velum, the mesoglea contains amoeboid mesenchyme cells, cnidocytes occur in the gastrodermis as well as the epidermis, and gametes are gastrodermal in origin
- Many scyphozoans are harmless to humans; others can deliver unpleasant and even dangerous stings
- Aurelia is a common scyphozoan in both pacific and atlantic coastal waters of north america
- The margin of its medusa has a fringe of short tentacles and it's divided by notches
- the mouth of aurelia leads to a stomach with 4 gastric pouches, which contain cnidocyte-laden gastric filaments
- radial canals lead from gastric pouches to the margin of the bell
- in aurelia, but not all scyphozoans, the canal system is extensively branched and leads to a ring canal around the margin of the medusa
- gastrodermal cells of all scyphozoans possess cilia to continuously circulate seawater and partially digested food
- aurelia is a plankton feeder
- at rest, it sinks slowly in the water and traps microscopic animals in mucus on its epidermal surfaces
- cilia carry this food to the margin of the medusa
- four fleshy lobes, called oral lobes, hang from the menubrium and scrape food from the margin of the medusa
- cilia on the oral lobes carry food to the mouth
- in addition to sentory receptors on the epidermis, aurelia has eight specialized structures, called rhopalium