BIOL 1101 Lecture Notes - Lecture 89: Mesoglea, Gastrodermis, Cnidaria
27 Jun 2016
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Document Summary
Two body forms are common among cnidarians - the medusa form and the polyp form. These two forms alternate in most cnidarian life cycles. The medusa floats in the water like an upside-down, tentacle-fringed bell. Pulsations of the bell allow it to swim. The polyp is usually a tube-shaped organism that is attached to a solid surface at one end and has a tentacle-fringed mouth at the other end. Hydra is a typical polyp, and sea anemones are larger polyps. The next screen shows diagrams of these two forms. For comparison, the medusa is drawn upside down. The black area in each drawing is jellylike mesoglea. The layer of cells inside the mesoglea is gastrodermis and the layer outisde the mesoglea is epidermis. The medusa is normally the motile part of the life cycle and the polyp is the non- motile or sessile part.
