40 Fun Facts About Comb Jellies (Ctenophores)

The rainbow colours that ripple along a comb jelly's sides when it swims are produced by what?

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.

Instead of a jellyfish's stinging cells, a comb jelly's tentacles carry cells that release what?

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.

Comb jellies have no brain, so which simpler system under the skin coordinates their swimming?

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.

Which sea's fisheries crashed in the 1980s after the sea walnut, an American comb jelly, invaded?

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.

In laboratory experiments, what can two injured sea walnuts do, even if genetically different?

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.

Like the so-called immortal jellyfish, what can an adult sea walnut do when put under severe stress?

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.

Why is the deep-sea bloodybelly comb jelly thought to have a stomach coloured dark red?

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.

Fossils thought to be comb jellies go back to which period, known for its 'explosion' of life?

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.

Which letter stays silent when biologists say 'ctenophore', the scientific name for a comb jelly?

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.

Which body opening does the sea walnut form only when it is needed, then seal over again?

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.

Comb jellies are the largest animals to swim using which tiny, hair-like structures?

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.

How many comb rows, the bands of beating plates that propel a comb jelly, do most species have?

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.

Which species, up to 1.5 metres long, is the largest of all known comb jellies?

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.

How did the sea walnut most likely cross the ocean to reach European seas in the 1980s?

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.

Catches of which small fish collapsed in the late 1980s as invading sea walnuts ate its eggs?

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.

The comb jelly Beroe seals its huge mouth shut while it swims in a way likened to what?

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.

Which fruit gives its name to Pleurobrachia, a small round comb jelly with two long tentacles?

Gooseberry-sized and nearly as round, the sea gooseberry trails tentacles up to twenty times its body length, then reels them back into pouches.

Some genome studies suggest comb jellies, not which simple animals, form the oldest animal branch?

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.

Comb jellies' hunting tricks, such as dangling a sticky droplet, are likened to which animals'?

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.

What does the statocyst, a tiny organ at the end of a comb jelly opposite its mouth, sense?

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.

Each sea walnut is both male and female, which allows a lone animal to do what?

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.

What do adult comb jellies do when food runs short, reversing the change once prey returns?

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.

Platyctenid comb jellies, which creep over the seabed and corals, are often mistaken for what?

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.

NOAA scientists named Duobrachium sparksae, a comb jelly found off Puerto Rico, using only what?

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.

When disturbed, a few comb jellies such as Euplokamis release a cloud of what into the water?

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.

Along its comb rows, the sea walnut flashes which colour when it is disturbed?

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.

Mertensia ovum, a comb jelly also known as the sea nut, lives mainly in which ocean?

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.

Early zoologists lumped comb jellies into one group, Coelenterata, with which other animals?

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.

A comb jelly's comb plates beat one after another in a rhythm likened to which crowd ritual?

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.

Comb jellies resemble jellyfish but differ so much that biologists give them their own what?

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.

Which landlocked sea did the sea walnut invade in 1999 by way of Russia's inland waterways?

The Caspian Sea lost about 60% of its sprat after the invader arrived, and the sturgeon and seals that eat them declined in turn.

Comb jelly neurons lack serotonin and dopamine, so which chemical messenger do they rely on instead?

Glutamate does the signalling, and comb jellies carry an unusually large set of receptors for it. Their odd chemistry is one reason some biologists think their neurons evolved separately from other animals'.

The comb jelly Bathocyroe fosteri honours Dudley Foster, a pilot of which research submersible?

Alvin pilot Dudley Foster collected the first specimens. The little jelly is common near the Mid-Atlantic Ridge, where it usually hangs motionless in the water.

Juvenile Lampea comb jellies cling like parasites to which barrel-shaped drifters that form chains?

Salps are the only food Lampea eats, and a juvenile too small to swallow one simply rides on it. That makes Lampea the one partly parasitic genus of comb jelly.

How do the comb jellies Ocyropsis and Bathocyroe use their two big mouth lobes to escape danger?

They clap them to jet away: the squirt of expelled water drives the animal backwards very quickly, a rare burst of speed in a group of slow swimmers.

In which country did sea walnuts reach salty inland lakes, carried in by accident with mullet fry?

Egypt's Lake Qarun, near Faiyum, yielded sea walnuts in 2013, and nearby Lake El Rayan II followed in 2014. Both lakes are salty, and Qarun is saltier than the sea.

What is the jelly layer called that fills a comb jelly's body between its outer and inner skins?

Mesoglea is mostly water, so it cannot hold the body up in air: lifted out of the sea, comb jellies and jellyfish alike flatten or collapse.

Comb jelly expert Steven Haddock says even textbooks make which mistake in their illustrations?

Drawing them upside down comes from assuming they swim like jellyfish, mouth facing down. In fact a comb jelly usually swims with its mouth leading the way.

Thalassocalyce inconstans is the only comb jelly whose fragile adult body takes which shape?

A bell like a jellyfish's lets it fish with the dome spread wide; when krill or other small prey touch the inside, it snaps shut and traps them in mucus.

Which reptiles join jellyfish and chum salmon among the animals that eat comb jellies in bulk?

Turtles and some jellyfish eat comb jellies in large quantities. Chum salmon digest them 20 times as fast as the same weight of shrimp, so a swarm makes a quick, easy meal.