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.

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

Did you know ?

Jellyfish bodies are made up of 95% water.

Lion's mane jellyfish, including tentacles, can reach over 230 feet long and 6.5 feet in diameter !

Sea turtles are the main predators of jellyfish.

Discover jellyfish

Atlantic sea nettle
(Chrysaora quinquecirrha)

Barrel jellyfish
(Rhizostoma pulmo)

Blue jellyfish
(Cyanea lamarckii)

Compass jellyfish
(Chrysaora hysoscella)

Lion's mane jellyfish
(Cyanea capillata)

Moon jellyfish
(Aurelia aurita)

Sea nettle
(Chrysaora fuscescens)

White spotted jellyfish
(Phyllorhiza punctata)

Our latestUpdates

Friday, September 5th 2025

The bump-head sunfish

Learn about the bump-head sunfish (Mola alexandrini), the world's heaviest bony fish, its habitat in tropical and temperate oceans, diet of jellyfish, deep-water behavior and record size over 6,000 lbs.

Wednesday, September 3rd 2025

The chocolate chip sea cucumber

The chocolate chip sea cucumber has a massive cylindrical body that is beige in color, covered with a set of dark brown pustules resembling chocolate chips that protrude slightly from the surface, giving it a resemblance to a cookie, hence its french name. It can reach a length of about 12 inches when fully grown.

Monday, September 1st 2025

The red hind grouper

The red hind grouper has a distinctive appearance, usually beige to brown in color, with numerous red or brown spots covering its entire body and the base of its fins. It is often found in the shallow waters of coral reefs and rocky areas, where it hides in crevices and cavities.

Photo of the Day

Sabelle sociale
(Bispira brunnea)