Aurelia aurita
This is one of the most common jellyfishes found on the beach in New Jersey. When washed up on shore they look like a round disk-shaped pad of fairly hard jelly, at least as far as jellyfish consistency goes. Most moon jellies you find will be about 4 or 5 inches in diameter. The disk that washes up on shore is just the last and most durable remnant of this creature. This video below shows a different species than the one the lives of the coast of New Jersey but its behavior and appearance is very similar to our local moon jellyfish.
One of the moon jelly's defining features is the interesting pattern in the center of the disk. In some it resembles a loosely arranged four leaf clover pattern. These are actually organs that are used for reproduction. This jellyfish is a carnivore and its diet is mostly plankton. They use stinging nematocysts to subdue the food they catch and also have a mucus layer that they pull food into. This sticky goo serves to trap their prey. Moon jellyfish tend to stay close to the water surface, in large part because this is where there is a lot of food for them. This behavior does make them susceptible to being eaten themselves and they are preyed upon by certain large fish, turtles and even some birds. Another consequence of living close to the water surface is they tend to be moved around by the tides fairly easily. They can move by manipulating their bell shaped body and thrusting water away from them. This only works to move them in one direction. This movement is often not enough to keep up with the water currents at the surface. Since their locomotion is not that efficient they are also susceptible to being washed ashore.
Fortunately the stingers of this species are relatively mild. Most people that come into contact with moon jellyfish have little reaction. Some may feel a bit of a stinging sensation but even this can be relatively mild compared to what can occur with more troublesome jellyfish species. Many moon jellies you find no longer have any stingers attached to them.
The first two pictures on this page are presented here under a creative commons license and were graciously provided by ethorson
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