Body Plan
Fact Sheet

Body Plan

The body plan of a Moon Jellyfish is in two different forms during its lifetime but both body plans are fairly simplistic.  The primary similarity between both stages is that they have radial symmetry.  Also, the basic body plan is a sac-like structure with an internal gastrovascular cavity.  The gastrovascular cavity has one opening which acts as both a mouth and an anus.  The opening is surrounded by tentacles which assist in feeding and protection.  

The body wall consists of three layers: the epidermis, the mesoglea, and the gastrodermis.  The epidermis is the outermost layer, the gastrodermis is the innermost layer, and the mesoglea is between the two. 

Moon Jellyfish do not have lungs, gills, or a tracheal system of any sort.  They simply receive oxygen by diffusion through their thin membrane.  Their large surface area to volume ratio increases their ability for diffusion. 

Cells called cnidocytes are found most abundant on the tentacles or oral arms.  In the cnidobcytes are nematocytes which sting as a form of protection. 

The first major stage is the polyp stage.  Two distinctive characteristics of this organism are that it is usually attached to a substrate and has a mouth that opens upward. 

The second major stage is the medusa stage which is characterized by a bell-shaped body, being free-swimming, and having a mouth that opens downward.   An identifiable characteristic of Moon Jellyfish is 4 violet or pink, crescent shaped gonads at the center of the bell-shaped body.