A jellyfish's body form is primarily a medusa. This is a free-swimming, bell-shaped form, characteristic of many cnidarians.
The Medusa Body Plan
The medusa body plan is characterized by its:
- Radial symmetry: The body is organized around a central point, like a wheel. This means that multiple planes can divide the body into roughly equal halves. (Hawaii.edu, AnimalDiversity.org)
- Umbrella-shaped body: The main body is a bell or dome-like structure, often translucent. (Britannica, AnimalDiversity.org)
- Tentacles: Numerous stinging tentacles hang down from the edge of the bell, used for capturing prey and defense. (Oceana, Smithsonian Ocean)
- Oral arms: These surround the mouth, located on the underside of the bell. They help to manipulate food. (Te Ara)
- Internal Cavity: Digestion takes place within a single internal cavity. (Te Ara)
Beyond the Medusa: Life Cycle Stages
While the medusa is the most recognizable form, it's important to note that jellyfish undergo a complex life cycle. Many species also have a polyp stage, which is a sessile (attached) form. The polyp stage is often less conspicuous and may be found in different locations than the adult medusa. (SCDNR, Chegg.com)
Jellyfish Body Composition
Jellyfish are primarily composed of water, with an outer layer (epidermis) and an inner layer (endodermis). A gelatinous mesoglea fills the space between these two layers. (NOAA, Juli Berwald)
