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Jellies

About AquaFacts: AquaFacts are a resource for students who are looking for information on the animals at the Aquarium or other Aquarium-related topics. Here, we’ve compiled some of the most frequently asked questions that we’ve received about jellies. The answers come from our biologists and from reputable sources that we reference at the end of this page. If you have a question about jellies that’s not addressed in this page or the references below, please feel free to email our librarian.

Jellies

Questions & Answers

What are jellies?

Jellies belong to the phylum Cnidaria, which has three major classes: Hydrozoa, the primitive fern-like creatures, many of which produce small jellies; Scyphozoa, the large jellies or scyphomedusae and their polyps; and Anthozoa, the sea anemones. Although many of these animals produce a jelly as part of their life cycle, there are only about 200 species of large jellies that people are likely to notice - most of these are in the class Scyphozoa.

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What is a jelly made of?

A jelly is an invertebrate made up mostly of water, and has no heart, brain or bones. It is made up of 96 percent water, 3 percent protein and 1 percent minerals.

Where can you find jellies?

Jellies live in all the world's oceans.

How do they swim?

Jellies swim by jet propulsion. The jelly will expand then quickly contract its bell-shaped body, which forces water away from the bell and pushes the jelly in the opposite direction.

Do jellies have eyes?

Jellies don't have eyes as we think of them, although some species have eyespots. Eyespots are light-sensitive spots on the rim of their bells called ocelli. Jellies also have sensory organs called rhopalia, which form a row of small round structures along the rim of the bell. The rhopalia include sensory organs called statocysts that help maintain the jelly's balance. When a jelly tips too far to one side, the statocyst will stimulate nerve endings that cause muscles to contract, turning the jelly right side up.

How do jellies avoid their predators?

Jellies are drifters and can't hide from predators, but some are transparent which keeps them hidden from hungry leatherback sea turtles and ocean sunfish.

How do jellies sting?

Jellies have specialized stinging cells, called cniodocytes. Each of these cells contains a nematocyst which acts like a mini-harpoon. When a jelly touches something the nematocyst is released and injects toxin into the prey.

What type of jellies does the Aquarium have?

Jellies you might see at the Aquarium include moon jellies (Aurelia labiata), lion’s mane jellies (Cyanea capillata), fried egg jellies (Phacellophora camtschatica), water jellies (Aequorea spp), Japanese sea nettles (Chrysaora pacifica), Pacific sea nettles (Chrysaora fuscescens), spotted jellies (Mastigias papua) and red eye medusas (Polyorchis penicillatus). Moon jellies are the species most likely to be on exhibit all the time.

How can I identify a moon jelly and where are they commonly found?

Moon jellies have a transparent, white bell rimmed with hundreds of short tentacles. They have four oral arms, which hang from the centre of the bell. The four horseshoe shapes in the centre of the bell are the gonads (sex organs) and the guts. The moon jelly has two distinct lifecycle stages; the polyp stage and a medusa or jelly stage. 

Moon jellies range from the Arctic to Florida and from Alaska to southern California. While swimming you may encounter huge masses of them (called smacks) drifting with the current near the beach. If you touch their tentacles their sting will not kill you, unless you are allergic to the toxin. It will probably feel tingly, but some people say they don't feel anything when stung by a moon jelly.

How long do jellies live?

They can live in the polyp, or budding, stage for as long as five years or more. During the medusa stage the jellies may live for several months.

What are the jellies at the Aquarium fed?

The jellies at the Aquarium are fed a daily meal of larval brine shrimp that have been enriched with fatty acids, as well as frozen copepods.

Can a jelly "repair" its damaged tentacles or other parts of its delicate body?

Yes, a jelly can regenerate small amounts of tissue that has been damaged.



Facts & References

Did You Know?

  • Australia’s box jelly is the most dangerous jelly. It has a lethal toxin more potent than cobra venom. It can kill a person in minutes.
  • Jellies have been in the Earth's oceans for over 650 million years; they were here before the dinosaurs.
  • The largest jelly has a bell that can reach 2.4 metres across and tentacles that extend over half the length of a football field.
  • Many people consider jellies a delicacy. They are dried and de-salted to provide a nutrient-rich, low fat, low-calorie meal. It could become the next diet-craze food.

References

  1. Monterey Bay Aquarium. Jellies: Online Field Guide.
  2. Wroebel, David and Claudia Mills. 1998. Pacific Coast Pelagic Invertebrates. Monterey Bay, CA: Sea Challengers.

Permission is granted by the Vancouver Aquarium Marine Science Centre for classroom teachers to make copies for non-commercial use. This permission does not extend to copying for promotional purposes, creating new collective works, or resale.

Jellyfish

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