Comb Jellies (Ctenophores)
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40 free Comb Jellies (Ctenophores) trivia questions with answers — trivia quiz, new questions added Oct 2026.
Ctenophores, better known as comb jellies, are some of the oddest animals in the sea. They look like jellyfish but are not, they shimmer with rainbow colours as they swim, and their kind has been drifting through the oceans since long before the first fish. This quiz gathers the best fun facts about ctenophores. It covers how comb jellies move, sense their surroundings and catch their prey, the tricks their bodies can pull off in the lab, the species with the strangest shapes and habits, and the story of one small invader that upended whole fisheries. A few questions touch on the science, from fossils to the argument over where these animals sit on the tree of life. It is written for curious readers, students meeting comb jellies in a biology class, and anyone who has watched one sparkle in an aquarium tank. Most questions can be reasoned out without a textbook, a handful are tougher, and every answer comes with a short explanation.
30 of 40 questions with answers and explanations. Play the quiz
Q 01The rainbow colours that ripple along a comb jelly's sides when it swims are produced by what?
Scattered light
Scattered light makes the rainbow: the tightly packed hairs of each beating comb plate break it into shifting colours, much as an oil slick does. The animal itself is making none of it.
Q 02Instead of a jellyfish's stinging cells, a comb jelly's tentacles carry cells that release what?
Glue
Glue bursts from cells called colloblasts when prey touches a tentacle, so comb jellies cannot sting swimmers. One genus, Haeckelia, cheats by reusing the stinging cells of jellyfish it eats.
Q 03Comb jellies have no brain, so which simpler system under the skin coordinates their swimming?
A nerve net
A nerve net runs beneath the skin, densest around the mouth, tentacles and comb rows. Many of its nerve cells merge into one continuous web, a wiring style that sets comb jellies apart from other animals.
Q 04Which sea's fisheries crashed in the 1980s after the sea walnut, an American comb jelly, invaded?
Black Sea
The Black Sea had nothing that ate the newcomer, and by 1989 it held up to 400 sea walnuts per cubic metre, all feeding on plankton and fish eggs.
Q 05In laboratory experiments, what can two injured sea walnuts do, even if genetically different?
Fuse into one animal
Two sea walnuts can fuse into one animal, joining even their nervous and digestive systems. Within about two hours, nearly all of the merged body's muscle twitches were in step.
Q 06Like the so-called immortal jellyfish, what can an adult sea walnut do when put under severe stress?
Grow young again
A stressed sea walnut can grow young again, turning from a lobed adult back into its early tentacled form. The discovery, reported in 2024, made it the first comb jelly known to do so.
Q 07Why is the deep-sea bloodybelly comb jelly thought to have a stomach coloured dark red?
To hide glowing prey
Its red gut is thought to hide glowing prey, which would otherwise shine through the see-through body and betray it. Red is nearly invisible in the deep sea.
Q 08Fossils thought to be comb jellies go back to which period, known for its 'explosion' of life?
Cambrian
Cambrian fossil beds up to 525 million years old hold soft-bodied animals read as comb jellies. Some from Canada's Burgess Shale carried as many as 80 comb rows, far more than living species.
Q 09Which letter stays silent when biologists say 'ctenophore', the scientific name for a comb jelly?
C
C is silent, so the word is usually said 'TEEN-o-for'. It comes from Greek words for comb and carry, after the rows of beating combs the animals swim with.
Q 10Which body opening does the sea walnut form only when it is needed, then seal over again?
Anus
The sea walnut's anus exists only while in use: the gut swells until it meets the skin, opens a pore, then closes without a trace. Adults go about once an hour.
Q 11Comb jellies are the largest animals to swim using which tiny, hair-like structures?
Cilia
Cilia bundled into rows of comb plates beat like tiny oars, and the biggest comb jellies they propel reach 1.5 metres long. Each plate holds thousands of them.
Q 12How many comb rows, the bands of beating plates that propel a comb jelly, do most species have?
8
Most species have 8 comb rows, running from one end of the body towards the other and spaced more or less evenly around it. The organs that make eggs and sperm lie in canals just beneath them.
Q 13Which species, up to 1.5 metres long, is the largest of all known comb jellies?
Venus girdle
The Venus girdle looks like a transparent belt with shimmering edges and swims by rippling its whole body. It drifts in warm oceans worldwide, eating small crustaceans.
Q 21Each sea walnut is both male and female, which allows a lone animal to do what?
Fertilise its own eggs
A sea walnut can fertilise its own eggs, and a large one may produce as many as 10,000 of them. Egg-laying can begin when the animal is only about 15 mm long.
Q 22What do adult comb jellies do when food runs short, reversing the change once prey returns?
Shrink
They shrink: a hungry comb jelly first stops making eggs and sperm, then gets steadily smaller, and returns to full size and to breeding when food comes back.
Q 23Platyctenid comb jellies, which creep over the seabed and corals, are often mistaken for what?
Flatworms
Q 14How did the sea walnut most likely cross the ocean to reach European seas in the 1980s?
In ships' ballast water
Travelling in ships' ballast water is the likeliest route, and the sea walnut was built for it: it tolerates almost any saltiness and water from 2 to 32 °C.
Q 15Catches of which small fish collapsed in the late 1980s as invading sea walnuts ate its eggs?
Anchovy
Anchovy, known locally as hamsi, was the region's key commercial catch. The sea walnut ate the fish's eggs and hatchlings and competed with the survivors for plankton.
Q 16The comb jelly Beroe seals its huge mouth shut while it swims in a way likened to what?
A zipper
A zipper is the comparison: the lips seal from each end to keep Beroe streamlined, then spring open to suck in prey, often another comb jelly larger than itself.
Q 17Which fruit gives its name to Pleurobrachia, a small round comb jelly with two long tentacles?
Gooseberry
Gooseberry-sized and nearly as round, the sea gooseberry trails tentacles up to twenty times its body length, then reels them back into pouches.
Q 18Some genome studies suggest comb jellies, not which simple animals, form the oldest animal branch?
Sponges
Sponges were long assumed to be the first branch, but a 2023 chromosome study backed comb jellies instead. If that holds, neurons and muscle cells either evolved twice or were lost along the way.
Q 19Comb jellies' hunting tricks, such as dangling a sticky droplet, are likened to which animals'?
Spiders
Spiders make a fair match: some comb jellies hang motionless with tentacles spread like a web, some pounce like jumping spiders, and some swing a sticky bead as bolas spiders do.
Q 20What does the statocyst, a tiny organ at the end of a comb jelly opposite its mouth, sense?
Balance
Balance comes from a chalky grain resting on four tufts of hairs, which feel its weight shift as the animal tilts. A clear dome protects the whole device.
Flatworms are the usual mix-up, because platyctenids are flat, nearly all lack comb rows and they glide along on a turned-out throat. Long branching tentacles streaming in the current give them away.
Q 24NOAA scientists named Duobrachium sparksae, a comb jelly found off Puerto Rico, using only what?
Video footage
Video footage from a robot submersible nearly 4 km down was all they had, since no specimen could be collected. The clips are kept at the Smithsonian as the species' type material.
Q 25When disturbed, a few comb jellies such as Euplokamis release a cloud of what into the water?
Luminous ink
Luminous ink shines at much the same wavelengths as the animal's own body. What the glow is for is still unsettled: studies have yet to pin down a purpose for comb jellies' light.
Q 26Along its comb rows, the sea walnut flashes which colour when it is disturbed?
Blue-green
Blue-green flashes come from cells in the canals beneath the comb rows. In Monterey Bay, more than 90 percent of comb jellies are bioluminescent.
Q 27Mertensia ovum, a comb jelly also known as the sea nut, lives mainly in which ocean?
Arctic
Arctic seas suit Mertensia ovum, which stays mostly in the top 50 metres, while most comb jellies prefer warmer water. It is the main bioluminescent drifter among the region's jelly-like plankton.
Q 28Early zoologists lumped comb jellies into one group, Coelenterata, with which other animals?
Cnidarians
Cnidarians, the jellyfish, corals and sea anemones, share the comb jellies' jelly-filled body and lack of a brain. But their cell layers are one cell thick, where a comb jelly's are two.
Q 29A comb jelly's comb plates beat one after another in a rhythm likened to which crowd ritual?
Mexican wave
A Mexican wave of beating plates runs down each comb row, each plate firing just after its neighbour. The wave starts at the end farthest from the mouth and travels towards it.
Q 30Comb jellies resemble jellyfish but differ so much that biologists give them their own what?
Phylum
Phylum is the rank just below kingdom, so the split from jellyfish is about as deep as animal classification goes. The comb jellies' group, Ctenophora, holds fewer than 200 known living species.