Structure of Jellyfish (Aurelia)

The scientific name of jellyfish is Aurelia. The common Jellyfish occurring in warm and temperate seas all over the world. It belongs to:

• PhylumCoelenterata
• ClassScyphozoa
• OrderSemaeostomae

Aurelia aurita is a moon jellyfish. It represents the dominant medusoid stage.

1. Shape and size of jellyfish (Aurelia): It looks like an umbrella. Its body is circular in outline. It is 4 to 12 inches in diameter. It is usually colorless, but transparent. It shows tetramerous radial symmetry.
2. Structure of jellyfish (Aurelia):
   1. The convex side of the umbrella is called exumbrellar surface.
   2. The inner concave surface of the umbrella is called sub-umbrella surface.
   3. The outline of the bell is circular with eight notches.
   4. The umbrella is thick in the middle and is thin on the margin. The umbrella of Aurelia will show the following parts.
3. Mouth and oral arms: In the middle of the sub umbrellar surface a very short and indistinct manubrium is present. At its free and tetrangular mouth is prominent. From the four corners of the mouth four long oral arms will arise. On the ventral side of each oral arm a ciliated groove is present. It leads into the mouth. The oral arms are present on per radial lines.
4. Sub-genital pits: On each 4 inter radii, 4 sub-genital pits are preset. They lead into a shallow cavity. Their function is not clearly known; they may up respiration.
5. Velarium: On the margin of the umbrella a fold is present. It is called Velarium. It is an ectodermal projection with endodermal core. Such medusae are called acraspedote medusae.
6. Lappets and tentaculocysts: On the margin of the umbrella at 4 inter radial and 4 per radial positions 8 lappets are present. In each notch a tenta culocyst is present. It is a sense organ.
7. Tentacles: On the margin of the umbrella a number of tentacles are present. The tentacles bear a number of chidoblasts.
8. Gonads: Just above the sub genital pit, on 4 inter radial positions 4 horse shoe shaped gonads are present on the floor of the stomach alternating with 4 gastric pouches.

Aurelia medusa will show a number of Radial Canals. They can be clearly seen in this transparent medusa. Four per radial, four inter radial and 8 ad radial canals are present. Some of them are branched. They are all connected with circular canal present on the margin of the medusa.

Aurelia is diploblastic zooid. It shows outer ectoderm and inner endoderm. In between these germ layers mesoglea is present. It is jelly like substance. Its quantify is more hence the medusa looks like a jellyfish.