Scyphozoans - Jellyfish  

Image courtesy of the NOAA Photo Library

Kingdom: Animalia
Phylum: Cnidaria
Class: Scyphozoa
Order: Semaeostomae, Coronatae,
Rhizostomeae, Stauromedusae

Image courtesy of California Department of Water Resources


Conservation Status

No scyphozoan species is currently listed as endangered or threatened by the United States Endangered Species Act, IUCN, or CITES.

Conservation Issues

In general, very little research has been done on scyphozoans. Our understanding is mostly limited to their lifecycles. Schyphozoans are difficult to study because of their polyp stage. Scientists had been unable to even locate the polyp stages of most jellyfish until very recently (Leffler, 1994). Also, jellyfish samples are hard to collect. Scientists use plankton nets to collect samples of marine plankton, but these often damage the soft gelatinous body of scyphozoans. The appearance of rapid increases in jellyfish populations, or "blooms," in certain regions has made apparent the need for further knowledge (Harbor Branch Oceanographic, 2001).

Scyphozoans are a very important part of marine food webs. They feed on phytoplankton, algae, and sometimes larvae of other organisms (Peterson, 2000). Jellyfish are good predators and frequently beat out other organisms in competition for the same resources (Mills, 2001). They can also negatively affect other populations by eating their young (Sea Grant, 2000). Because of this close relationship with other organisms, some scientists suggest that habitat health can be measured be scyphozoan populations (Peterson, 2000).

Jellyfish "blooms" have been observed in many areas including, the Gulf of Mexico, the Black Sea, the Chesapeake, Japan, the Mediterranean and the Bering Sea (Leffler, 1994; National Aquarium in Baltimore, 2000; Peterson, 2000; Sea Grant 2000; Mills 2001). Most scientists believe that the health of an environment plays a large part in appearance of blooms, but some think other factors are involved. Jellyfish blooms in the Chesapeake have been attributed to fluctuations in weather patterns (National Aquarium in Baltimore, 2000). However, all scientists agree that lots more research must be done on jellyfish if we are to understand how they interact with their environment.


Conservation Organizations

Dock Watch- an ongoing, volunteer-powered conservation study of jellyfish blooms along the southeastern coast.

Monterey Bay Aquarium - They "work to advance [ocean] conservation through education and research."

Marine Conservation- Covers recent research on jellyfish populations and related marine conservation issues.

Other Fun Stuff

My Life as a Blob - Lots of cool pictures!

The Jellies Zone- check out the Jellies Gallery and Jellies in the News

The Bioluminescence Page- Learn the chemistry behind the jellyfish glow.

Image Courtesy of NOAA Photo Library


Physical Characteristics

Jellyfish are radially symmetrical invertebrates easily characterized by their bell, or medusa, shape. Features include a simple nerve net with sensory cells; a gut cavity with one opening for food, waste, and sex gametes; a layer of jelly, or mesoglea; and several oral arms and tentacles radiating from the gut area. Jellyfish consist of 96% water and range in diameter from 2 cm to 2 m (Cnidarian Research Institute, 2001).


Each oral arm tentacle contains thousands of special cells (cnidoblasts) that use water pressure to shoot out a venomous harpoon-like nematocyst whenever they are triggered by touch. All scyphozoans have some stinging capacity, and many are bioluminescent, a feature which can intimidate predators (Wrobel, 1998).


Carnivorous, jellyfish mostly eat plankton and larval fish. After stunning prey with their tentacles, jellyfish use their oral arms to bring the food to their mouth.

Life Cycle

Reproduction is sexual in the dominant medusa stage, and the resulting larva forms a polyp which reproduces asexually by budding off tiny baby medusae which then develop into adults. Most scyphozoans are thought to live about a year in the wild (Wrobel,1998).

Image courtesy of Sea Science

Distribution and Habitat

Exclusively marine, scyphozoans inhabit every ocean in the world. They are most commonly found close to shore in shallow waters, and usually thrive in eutrophic conditions.

Movement and Behavior

Scyphozoans possess special sensory cells and water-propulsion muscles to control balance and movement to some degree. However, they cannot actively swim against a current, and are therefore classified as planktonic drifters. Predation and other interactions are passive (Cnidarian Research Institute, 2001).

Literature Cited

Allison-Bunnell, S. and D. Wrobel. 1998. My Life as a Blob- All Jelly Slide Show. Accessed 2001 November.

Cnidarian Research Institute. 2001 August 14. Homepage. Accessed 2001 October 28.

Haddock, S.H.D.; McDougall; C.M.; Case, J.F. 2000. The Bioluminescence Web Page. 2001 October 28.

Harbor Branch Oceanographic. 2001. Marine Science - Water Column Ecology. 31 October 2001.

Leffler, Merrill. Jul-Aug 1994. Jellyfish: Studying Summer's Unwelcome Visitors. Accessed 31 Octoter 2001.

Mills, C.E. 21 July 2001. Marine Conservation. Accessed 31 October 2001.

National Aquarium in Baltimore. 2000. Chesapeake Bay, Ouch. 31 October 2001.

Peterson, Patrick. 26 August 2000. Numbers grow, Ecology Threatened. Accessed 29 October 2001.

Sea Grant. 8 September 2000. Giant Jellyfish Invade Northern Gulf of Mexico; Could Threaten Gulf Shrimp, Crab Fisheries. Accessed 31 October 2001.

Waggoner, B. 1996. Introduction to the Scyphozoa. Accessed 2001 October 28.

Wrobel, D. 1998. The JelliesZone. Accessed 2001 November 4.


Author: Heather Meckel and Lindsay Enders
Creation/revision date: 14 November 2001

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