Jellyfish or jellies are the major non-polyp form of individuals of the phylum Cnidaria. 

They are typically free-swimming marine animals consisting of a gelatinous umbrella-shaped bell and trailing tentacles. The bell can pulsate for locomotion, while stinging tentacles can be used to capture prey.


A purple-striped jelly at the Monterey Bay Aquarium. image: Sanjay Acharya/wikipedia


Kingdom: Animalia

Phylum: Cnidaria

Subphylum: Medusozoa

Classes include:

  • Cubozoa
  • Hydrozoa
  • Polypodiozoa
  • Scyphozoa
  • Staurozoa

Jellyfish are found in every ocean, from the surface to the deep sea. Scyphozoans are exclusively marine, but some hydrozoans live in freshwater. Large, often colorful, jellyfish are common in coastal zones worldwide. 

Jellyfish have roamed the seas for at least 500 million years, and possibly 700 million years or more, making them the oldest multi-organ animal.

Origin of the name ‘jellyfish'

The English popular name jellyfish has been in use since 1796.  It has traditionally also been applied to other animals sharing a superficial resemblance, for example ctenophores (members from another phylum of common, gelatinous and generally transparent or translucent, free-swimming planktonic carnivores now known as comb jellies) were included as "jellyfishes”.

Locations parts of a Jellyfish


Main descriptive orientations of a jellyfish. image: Nordelch/wikipedia

The parts include:

Most of the umbrella mass is a gelatinous material — the jelly — called mesoglea which is surrounded by two layers of protective skin. The top layer is called the epidermis, and the inner layer is referred to as gastrodermis, which lines the gut.

Source: Jellyfish. (2015, January 14). In Wikipedia, The Free Encyclopedia. Retrieved 03:38, January 16, 2015, from