Moon Jellyfish
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40 free Moon Jellyfish trivia questions with answers — trivia quiz, new questions added Oct 2026.
Moon jellyfish are the pale, pulsing jellies most people picture when they think of a jellyfish tank. They look simple, but almost everything about them is strange: how they are built, how they find a meal, and how one animal can pass through several completely different shapes in a single lifetime. This quiz turns the best moon jellyfish fun facts into questions. It covers the body and senses, feeding and predators, the sting, the life cycle, the science behind the names, and a few surprising run-ins with people, from laboratories to power stations. It is pitched for curious beginners, students and families, with a handful of tougher questions for keen jelly watchers. Every answer comes with a short explanation, so you leave knowing more than when you started.
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Q 01Which space shuttle carried nearly 2,500 young moon jellyfish into orbit in 1991 to study weightlessness?
Columbia
Columbia carried the jellies as the lone jellyfish experiment on a nine-day life-sciences mission, flying alongside studies of humans and rodents.
Q 02Which country's Oskarshamn nuclear plant shut a reactor in 2013 after moon jellyfish clogged its cooling pipes?
Sweden
Sweden's plant, home to one of the world's largest reactors, had tons of the jellies cleared from its pipes before it could restart.
Q 03What are the four horseshoe shapes visible through the top of a moon jellyfish's see-through bell?
Reproductive organs
Reproductive organs, known as gonads, form the four horseshoes, and they are the mark by which a moon jelly is most readily recognized.
Q 04Roughly how much of a moon jellyfish's soft, translucent body is made up of nothing but water?
About 95%
About 95% is water, leaving only a sliver of solid matter, which is why a jelly lifted out of the sea slumps into a shapeless blob.
Q 05Which of these body parts does a moon jellyfish get through life without?
Brain
Brain, heart and eyes are all missing, yet a simple net of nerves lets a moon jelly smell, taste and tell light from dark.
Q 06Which collective noun, heard alongside the term bloom, names a group of moon jellyfish swimming together?
A smack
A smack is the traditional word for the gathering, and a single one can hold hundreds or even millions of moon jellies near the surface.
Q 07Moon jellyfish share the famous snorkeling spot Jellyfish Lake with golden jellies in which Pacific nation?
Palau
Palau's lake sits on the island of Eil Malk, where the golden jellies cross the water every day while the moon jellies keep no such schedule.
Q 08Which sea turtle, the largest alive, lives almost entirely on jellies such as moon jellyfish?
Leatherback
Leatherback turtles follow jellies up and down the water column all day, and their appetite helps keep jelly numbers in check.
Q 09Which floating litter do sea turtles often swallow after mistaking it for a moon jellyfish or another jelly?
Plastic bags
Plastic bags adrift in the sea look just like jellies to a hungry turtle, and a swallowed bag can block the animal's gut.
Q 10Studies of the moon jellyfish showed that jellyfish are which kind of swimmer, compared with all other animals?
The most energy-efficient
The most energy-efficient swimmers known, they let the springy bell bounce back by itself, traveling 30 percent farther on each stroke.
Q 11A 2015 study found moon jellyfish share which rare ability with the tiny jellyfish Turritopsis dohrnii?
Aging in reverse
Aging in reverse, the trick that earned Turritopsis the nickname immortal jellyfish, lets a moon jelly turn back from an adult into a young polyp.
Q 12What can moon jellyfish do to survive when prey runs short, then undo once meals return?
Shrink their bodies
Shrink their bodies is the trick: a hungry moon jelly can dwindle to one-tenth of its size, then grow back when food becomes available again.
Q 13What can tint a normally colorless moon jellyfish pink, lavender or orange for a while?
What it has eaten
Q 21Moon jellyfish trap tiny prey on their bells with which sticky substance before sweeping it toward the mouth?
Mucus
Mucus coats the bell and snags passing prey, then beating hairs called cilia carry the catch to the rim to be passed on to the mouth.
Q 22What is the main food of moon jellyfish as they pulse and drift through coastal waters?
Zooplankton
Zooplankton, tiny drifting animals such as copepods, is the staple, though moon jellies also catch fish eggs, small mollusks and even other little jellies.
Q 23Where on her body does a female moon jellyfish carry her developing young before releasing them as larvae?
On her oral arms
What it has eaten shows through the clear body: certain crustaceans turn a moon jelly pink or lavender, while brine shrimp turn it orange.
Q 14Jellies such as moon jellyfish are kept in round 'kreisel' tanks, named after the German word for which toy?
Spinning top
Spinning top is what kreisel means, and the tank's slow circular flow keeps delicate jellies from being hurt by pumps or by the tank itself.
Q 15Which naturalist gave the moon jellyfish its first scientific name in 1758?
Carl Linnaeus
Carl Linnaeus, the father of modern taxonomy, listed the species in the tenth edition of his Systema Naturae, the starting point for naming animals.
Q 16Which kind of evidence revealed that the worldwide moon jellyfish is really more than two dozen look-alike species?
Genetic samples
Genetic samples split one supposedly worldwide species into at least 28, most of them very hard to tell apart by looks alone.
Q 17The seafloor 'polyp' stage of a moon jellyfish takes its name from a French word for which sea animal?
Octopus
Octopus is poulpe in French, and the naturalist Réaumur picked the name because a polyp's ring of writhing tentacles looked like one.
Q 18The swimming adult stage of a moon jellyfish is named after which figure of Greek myth?
Medusa
Medusa gave her name to the bell-shaped adult form and to Medusozoa, the wider group of animals that pass through such a stage.
Q 19Tiny mineral grains called statoliths, set around a moon jellyfish's bell, help the animal sense what?
Gravity
Gravity pulls on the grains so the eyeless jelly can orient itself in the water, while light-sensing spots called ocelli tell bright from dim.
Q 20With no gills or lungs, how does a moon jellyfish breathe as it drifts along in the sea?
Through its skin
Through its skin: the thin membrane covering a moon jelly's body lets the gas it needs seep straight in from the surrounding seawater.
On her oral arms, the frilly flaps around the mouth, small pits act as a temporary brood chamber for the growing larvae.
Q 24Moon jellyfish belong to the phylum Cnidaria, which makes which animals their close relatives?
Corals and sea anemones
Corals and sea anemones carry the same kind of stinging cells as a moon jelly, the feature shared by all 11,000 or so cnidarian species.
Q 25Cnidaria, the phylum of the moon jellyfish, takes its name from the ancient Greek word for which plant?
Nettle
Nettle is knide in ancient Greek, a nod to the coiled stinging threads that every cnidarian carries in its cells.
Q 26Which disc-shaped giant, one of the world's heaviest bony fishes, is a known predator of moon jellyfish?
Ocean sunfish
Ocean sunfish, or Mola mola, were once thought to live mainly on such prey, but jellies and salps turn out to be only about 15% of their diet.
Q 27Caltech biologists found a young moon jellyfish that loses limbs rearranges the rest to restore which trait?
Its symmetry
Its symmetry returns within about four days as the surviving limbs space themselves evenly, a kind of self-repair the team named symmetrization.
Q 28The bell of a full-grown moon jellyfish is often compared in size to which household object?
A dinner plate
A dinner plate is about the size of a typical adult bell, around a foot wide, yet every moon jelly starts out as a larva less than a millimeter long.
Q 29What do keepers at the National Aquarium adjust in the tank to control when moon jellyfish breed?
Temperature
Temperature is the switch: in the wild, the seasonal warming and cooling of the sea tells seafloor polyps when to bud off new young jellies.
Q 30What do biologists call the tiny free-swimming young that bud off a moon jellyfish polyp on the seafloor?
An ephyra
An ephyra is only about 4 millimeters across when it swims free, and a single polyp can release tens of them.