Sealife guideJellyfish: drifters of the oceanThe marine cnidarians

Last updated on 09/08/2025 at 11:26 PM

The barrel jellyfish (Rhizostoma pulmo) © Seadam | Dreamstime.com

Taxonomy

Phylum: Cnidaria
Class:

Common name: Scyphozoans
Scientific name: Scyphozoa

Description

Scyphozoans refer to the class of cnidarians that includes jellyfish. Scyphozoans comprise more than 4,000 species.

The name scyphozoan comes from scyphos meaning cup and zoon meaning animal.

Jellyfish are invertebrates with a gelatinous body consisting of a disc called a bell, with a mouth at its center surrounded by arms called oral arms.

The body of jellyfish is made of mesoglea, a mixture of collagen and water up to 95%, giving them their translucent appearance.

Anatomy of a jellyfish

Jellyfish have fine, long tentacles around the bell equipped with stinging cells.

The 'fried egg' jellyfish gets its name from its resemblance to the dish of the same name!

Jellyfish can move by propelling water through contractions of their bodies, but they are carried along by ocean currents.

It's hard not to feel 'tiny' in front of this gigantic black jellyfish during its occasional appearances in the coastal waters of southern California.

Jellyfish fish like a trawler, using their stinging tentacles to capture any animals that cross their path.

Jellyfish reproduce by releasing their gametes into the water.

Geographic range

Jellyfish are found in all oceans and at all depths, from the surface where they are most common to the deep sea.