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Moon Jelly


Other Common Names: saucer jelly, common sea jelly
Order: Semaestomeae
Genus & Species: Aurelia aurita
Family: Ulmaridae


Common and stable.


Worldwide in temperate and tropical oceans and bays.


Open water near coastlines; most common in bays and harbors.


In the wild adults live 3-6 months; polyps can live several years. Adults live up to several years in captivity.


Moon jellies are carnivorous, feeding on plankton including small shrimp, fish eggs, and larvae.  Food is caught in a layer of mucus and moved by cilia to the edge of the bell. From there it is removed by the oral arms and passed to the mouth.  Occasionally the small tentacles that surround the bell are used to catch small fish and other prey.


Moon jellies have a translucent saucer-shaped body with four distinctive horseshoe-shaped reproductive organs and four stocky oral arms surrounding the mouth; the bell can be up to 15 inches in diameter with its outer edge fringed with many small tentacles.


The moon jelly’s life cycle is complex and involves an alternation of generations in which the animal passes through two different body forms, a free-floating medusa and an attached polyp.  The familiar moon jelly is the medusa form which reproduces sexually.  Males release sperm into the water. Some sperm are swept into the mouth of a female where fertilization occurs.  Early development occurs inside the female or in brood pouches along the oral arms.  Small swimming larvae called planulae are released into the water.  After a few days the planulae settle to the sea floor and transform into flower-like polyps.  They use tentacles to feed on microscopic organisms in the water.  Polyps reproduce asexually by producing buds which develop into new polyps.  When conditions are right, polyps produce a larval stage (called a strobila) that looks like a stack of saucers.  Each saucer develops into a tiny free-swimming medusa (called an ephyra) which separates itself from the stack and grows into an adult moon jelly.

Ecology, Adaptations, Etc:

Moon jellies are members of a phylum of structurally simple marine invertebrates characterized by radial symmetry, a digestive cavity with a single opening for both the mouth and anus, a life cycle that includes medusa and polyp stages, and the presence of stinging cells called nematocysts . This phylum includes sea anemones, sea whips, corals, hydroids, jellyfish, and colonial siphonophores like the Portuguese man-of-war.

Adult jellies depend upon wind, tides, and currents to move them horizontally; they can control their vertical movement somewhat by rhythmically contracting their bells.

Moon jellies are equipped with special stinging cells (nematocysts) which they use for feeding and defense.  These cells are concentrated on the tentacles and oral arms.  When the jelly contacts an object, it triggers hundreds or thousands of these cells which each inject a small amount of toxin.  Usually this paralyzes or kills only small fish and crustaceans, but sometimes swimmers can be stung when they come into contact with jellyfish tentacles.  Usually these stings result in minor discomfort; more serious reactions occur mostly in tropical or warm temperate waters.

Moon jellies are an important part of many marine food webs.  They are prey for ocean sunfish, leatherback sea turtles, some larger jellyfish, and some sea birds.