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The Explorer's Guide contains a treasure trove of aquatic science resources developed for use in K-12 classrooms. Back to Explorer's Guide.

Pacific Sea Nettle Scientific Name: Chrysaora fuscescens
Don’t be fooled by the beauty and grace of the Pacific sea nettle. Its golden bell and long undulating red tentacles are equipped with thousands of painful stinging cells called nematocysts. The nematocysts lodge tiny paralyzing barbs into prey, making it impossible for escape. Long white oral arms hanging from the center of the bell begin digestion as they transport the prey to the nettle’s mouth.

Region: Philippines

This colorful creature is squishy and round and has what appears at first to be long legs. The Pacific sea nettle has a golden-brown bell or round top with a reddish tint. The bell can be up to a foot (30 cm) in diameter and has 24 deep red tentacles hanging off the edge of it. The long lacy white arms hanging from the middle of the bell are the oral arms, which are used in feeding. These arms may trail behind the bell for about 10 feet (3 m).

These sea nettles can swim against any current with the oral arms and tentacles extended. Swimming by means of jet propulsion by squeezing their bell, sea nettles push water behind them so they can move up and down in the ocean. Most of the time they just float. Sometimes they even pick up hitchhikers—small fish and crabs which hide inside the sea nettle's bell.

Pacific sea nettles live in all areas of the Pacific Ocean and Indian Ocean.

Pacific sea nettles can’t chase down their prey. They eat as they drift. Spreading out their tentacles like a large net, these nettles catch food as it floats by them. Prey includes fish eggs, baby fish, adult fish, other jellies and tiny floating animals.

When prey brushes up against a sea nettle, thousands of nematocysts or stinging barbs on its tentacles explode, launching barbed stingers into the victim. A paralyzing poison is injected from these stingers. The oral arms act as a digestive organ for prey too large to fit into its mouth.

In contrast to their simple structure, Pacific sea nettles have a very complex life cycle made up of five stages. They go through a metamorphosis or change in shape as they grow. Their lifecycle begins when males broadcast or release sperm into the water and the females catch the sperm to fertilize the eggs she has produced and is holding in her mouth. The fertilized eggs remain attached to the mother’s oral arms and grow into a flat jelly bean-shaped planula. The planula then grows into flower-shaped polyps and the mother releases them into the ocean. The polyps attach to a solid surface and undergo asexual reproduction through which they make an exact copy of themselves without eggs and sperm. The polyp makes these identical animals by budding where the new polyp grows out of its side. After the new polyp is fully formed, it is released into the ocean and starts to change shape, looking more like the adult nettle. The nettle develops a bell, arms and tentacles until it is a fully formed medusa or adult.

>A species or group of organisms that is in danger of extinction or disappearing from the face of the earth in the near future if its situation is not improved.

A species that can be found throughout its natural range but is declining in number and may become endangered in the absence of special protection efforts.

A species that is not declining in number but is of special concern because it is sensitive to pressure by particular human activities or natural events.

A species that is not declining in number and is not sensitive to pressures by human activities or natural events.

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Threats and Management
Thousands of Pacific sea nettles may gather in an area for months at a time. This can clog up large fishing nets causing the fishers to lose a great deal of money.

Did You Know?
Sea nettles are made up of 95 percent water. The other five percent is protein and salt.
Corals and anemones are the closest relatives of sea nettles. They are all part of a group of animals which all have stinging cells.
Sea nettles can’t see. They don’t have eyes, but they have rhopalia or light sensing organs. The rhopalia are located around the rim of the bell and help the sea nettle detect changes in light. They can’t make out distinct shapes, colors or details, but these light sensing organs enable the animal to move toward or away from light.
Sea nettles have a simple body tissue organization. They have a thin ectoderm or outer skin layer and a thin endoderm or inner skin layer. The ectoderm serves as a protector, while the endoderm helps in the digestion of food. Between the two layers, forming the bulk of the volume of the animal, is the mesoglea or jelly-like layer. The mesoglea helps to keep the sea nettle organized and helps maintain its shape. It provides a place for bell muscles to pull from. Sea nettles lack any true organ systems, and survive without a heart, brain, liver or kidneys.
Being almost jelly-like and transparent or clear, sea nettles use this quality as a defense mechanism. Since they don’t swim very well and they don’t have a hard protective body covering, their light-colored, almost transparent bodies keeps them out of sight from their predators.

It is eaten by sea turtles, large fish like the ocean sunfish and sea birds.

Print Publications:
Campbell, E., Kopp, K., and McCann, A. 1992. A Guide to the World of the Jellyfish. Monterey, California: Monterey Bay Aquarium Foundation. 16p.
ISBN# 1-878244-08-6.

Perrine, D. 1997. Mysteries of the Sea. Lincolnwood, Illinois: Publications International, Ltd. 312p. ISBN# 0-7853-2430-5.

Wrobel, D. and Mills, C. 1998. Pacific Coast Pelagic Invertebrates. Philippines: Sea Challengers. 112p. ISBN# 0-9301-1823-5.

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Vocabulary Words

Asexual Reproduction – Reproduction that does not involve the union of egg and sperm; results in an exact copy of the original animal.

Bell – The round part or top of a sea nettle or sea jelly.

Broadcast – A method of reproduction in which hundreds and even thousands of eggs and sperm are released into the water where they are intended to unite.

Budding – A form of asexual reproduction where the animal grows a new individual that is an exact copy out of the side of it.

Ectoderm – A thin outer skin layer.

Endoderm – A thin inner skin layer.

Ephyrae – The free-swimming, immature medusa produced asexually by the polyp.

Extinction – An organism that has not been present on the face of the earth for over 50 years.

Medusa – The adult, free-swimming form which has an umbrella-shaped bell, tentacles and oral arms; reproduces sexually.

Mesoglea – A jelly-like layer.

Metamorphosis – A change in the body form of an animal when changing from egg to adult.

Nematocyst – Stinging barbs like tiny harpoon-like stingers which deliver a paralyzing poison sting to stun or kill prey.

Oral arms – The arms used in feeding.

Organism – A living thing.

Planula – The fertilized egg produced by the medusa; a free swimming, flat pear-shaped organism which moves with the aid of tiny hairs called cilia.

Polyp – An animal that does not move because it is attached to a hard substrate; resembles a flower with the bottom of its stalk attached to a stable surface and tentacles and oral arms facing upward; reproduces asexually

Rhopalia – Light sensing organs located around the rim of the bell that enable the animal to move toward or away from light.

Species – A group of organisms capable of breeding and producing fertile offspring; organisms that share the same gene pool.

Transparent – Clear; see-through.

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Pacific Sea Nettle
Pacific Sea Nettle

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