BellThe body of the jellyfish, shaped like an umbrella. It tightens and relaxes to push the animal through the water.
TentaclesA fringe of short fine threads all round the rim. They carry stinging cells and catch small animals that drift into them.
Oral armsFour long frilled arms that hang from the corners of the mouth. They carry stinging cells and move food up to the mouth.
StomachA hollow in the middle of the bell where food is digested. Its only way in or out is the mouth.
MesogleaThe thick, clear jelly between the outer skin and the inner lining. It makes up most of the bell and gives it its shape.
ManubriumA short stalk that hangs from the middle of the underside. The mouth is at its tip. In a moon jelly it is very short.
From below 7
MouthThe one opening of the body, four-sided in a moon jelly. Food goes in through it, and waste comes out the same way.
GonadsFour horseshoe-shaped organs that make eggs or sperm. They show through the top of the bell and are how a moon jelly is known.
Gastric pouchesFour pockets that open off the stomach. One gonad lies in the floor of each.
Radial canalsThin tubes that run from the stomach out to the rim. They are set like the spokes of a wheel, and some of them branch.
Ring canalA narrow tube that runs all the way round the rim. Every radial canal opens into it.
Rhopalia (sense organs)Eight small sense organs, one in each notch of the rim. They help the jellyfish keep its balance and tell light from dark.
Marginal lappetsSmall flaps on the rim, one on each side of every notch. A sense organ sits between each pair.
How this list was compiled: Every name checked on 2026-10-01 in two sources. Wikipedia, Jellyfish (Anatomy), Aurelia aurita and Rhopalium, https://en.wikipedia.org/wiki/Jellyfish. NOAA National Ocean Service, What are jellyfish made of?, https://oceanservice.noaa.gov/facts/jellyfish.html. Animal Diversity Web, University of Michigan Museum of Zoology, Aurelia aurita, https://animaldiversity.org/accounts/Aurelia_aurita/. T. J. Parker and W. A. Haswell, A Text-book of Zoology, volume 1 (1910, public domain), the common jelly-fish, https://archive.org/details/textbookofzoolog00park. R. W. Hegner, College Zoology (1912, public domain), Aurelia, https://archive.org/details/collegezoology00hegn. Licence: own work
The drawing: Drawn for this site on 2026-10-01 from plain geometry; nothing traced. Licence: own work
How it works
The body parts of a jellyfish, drawn on a moon jelly. The first view shows it from the side, with the bell see-through as it is in life. The second looks at it from below. It is a plan, not to scale.
Read the full guide
From the side
The bell is the body. Most of it is mesoglea, a thick clear jelly. The stomach is the flat hollow in the middle, and the short manubrium hangs under it with the mouth at its tip. Four frilled oral arms hang from the mouth, and a fringe of short tentacles runs round the rim.
From below
Switch to Below. The mouth is in the middle. Four gastric pouches open off the stomach, each with a horseshoe-shaped gonad. Radial canals run out to the ring canal at the rim. Each notch of the rim holds a sense organ between two lappets. Press Quiz me to name each part yourself.
A jellyfish has no brain, no heart and no blood. A net of nerves spread through the body does the sensing.
Questions and answers
What are the body parts of a jellyfish?
A bell made mostly of jelly, a mouth under it that opens into a stomach, oral arms round the mouth and tentacles round the rim. A moon jelly also shows four horseshoe-shaped gonads, a set of canals and eight sense organs.
What is a jellyfish made of?
Mostly water, about 95 percent. The body has an outer layer, an inner layer and between them a thick, elastic jelly called mesoglea.
Do jellyfish have a brain or a heart?
No. A jellyfish has no brain, no heart and no blood. A simple net of nerves lets it sense light, smell and touch.
What are the four circles on a moon jellyfish?
Its gonads, the organs that make eggs or sperm. There are four, each bent like a horseshoe, and they show through the top of the clear bell.