to download a pdf of "What Jellyfish Are Not."

tentacleW hat Jellyfish AreNO T You can learn a lot about jellyfish . . .by learning what they’re not!oral armby Kathy KrankingNot Jelly, Not FishNope—even thoughthey’re called “jellyfish,” thatname doesn’t really describethese animals. For one thing,they certainly aren’t made ofjelly—at least not the kind you’deat in a sandwich. Jellyfish aremade mostly of water with asmall amount of thick gel. Also,jellyfish aren’t fish at all. They’reinvertebrates (animals withoutbackbones) and are cousinsto corals and sea anemones.So a better name for them isjust “jellies.”Not Look-AlikesDifferent kinds of jellyfish canhave very different looks. Theycan be as small as a rice grainor wider than you are tall. Andthey come in a rainbow ofcolors, even ones that glow inthe dark!Not YourAverageAnimalCheck out thisbeautiful purplestripedjellyfish as itswims along upsidedown. You can see thatjellies are unusual-lookingcreatures. Unlike most otheranimals, a jelly has no head,bellface, legs, or feet. Instead, a jelly’sbody is made up of an umbrellalikebell and dangling tentacles.Depending on the species, a jellycan have just a few tentacles orhundreds of them (though somekinds have no tentacles at all). Thejelly’s mouth is at the bottom ofits bell. It may be surrounded byfrilly oral arms, which move foodto the mouth when the jelly eats.INGO ARNDT/MINDEN PICTURES >; ART BY JIM PAILLOT1819

illustrationThe egg yolk jelly (left) eatsother jellyfish. So it has stickytentacles to help it hang on toits slippery, squishy prey. Thebluefire jellyfish at right hasused its stinging cells to catchan unlucky fish.Not BrainyJellies differ from other animalson the inside, too. A jelly hasno heart, no blood, no bones—not even a brain! But jellies getalong just fine without thesethings. They have nerves that,depending on the species, maylet them sense when they aretouching something, whetherthey are right side up or upsidedown, whether they are in lightor darkness, or even what odorsare in the water around them.Not HuggableImagine how hard it would beto catch food if you were a soft,squishy blob with no teeth orclaws. That’s how it is for jellies,so they have a secret weapon.Along their tentacles and sometimesalso on their oral arms,they have tiny stinging cellscalled nematocysts (nuh-MATuh-sists).These contain eventinier harpoons full of venom.The venom can stun or kill prey.Though some kinds of jellies areharmless to people, others cangive a nasty sting, and a few areeven deadly.Not Good SwimmersWith no fins or flippers, jelliesare weak in the swimmingdepartment. A jelly swims bysqueezing muscles at the bottomof its bell. This pushes wateraway, gently moving the jelly inthe opposite direction. Anotherway jellies get around is bysimply drifting along with theocean currents.Jellies don’t stalk or chasetheir prey. Instead, they swim ordrift with their tentacles danglingbeneath them. When a fishor other small creature bumpsinto the tentacles, it gets zappedby the jelly’s stingers. Then theoral arms move the prey to thejelly’s mouth.Some kinds of jellies, such asthe barrel jelly at right, haveno tentacles or central mouth.Instead they have hundreds oftiny mouths along theiroral arms. The mouthstake in tiny creaturesfloating inthe water.Check out this colorful crownjelly. Like many other jellies,it has glowing lights that itcan flash. The flashing lightsmight protect the jelly by confusingor startling an enemy.20TOM STACK/tom stack & assoc. (20); SUE DALY/NATUREPL.COM (21TL); FRÉDÉRIC PACOREL/BIOSPHOTO (21TR); DAVID WROBEL/VISUALS UNLIMITED > (21B) 21

Not a Good MealThanks to their stingers, jellieshave few predators. Mostanimals don’t want to tanglewith them. But there are some,including sea turtles (right)and certain fish, that can eatjellyfish. Somehow, they’re notbothered by the stingers.Not Always LonersThough most animals steerclear of jellies, some are actuallyjelly tagalongs. Certain fishand other creatures will use ajelly as a kind of bodyguard.For example, wearing a stingingupside-down jelly on its backcan keep the crab at right safefrom enemies. Other tagalongsstay close to a jelly or even rideinside its bell.There are different ideasabout why the tagalongs aren’tharmed by the jelly. For example,they may be covered withmucus that keeps the stingersfrom firing, or perhaps they arejust careful not to touch thejelly’s tentacles.So now that you’ve learned allthe things that jellies are not, youknow exactly what they are! =AMAR & ISABELLE GUILLEN/SEAPICS.COM (22T); JÜRGEN FREUND/NATUREPL.COM (22B);MICHAEL PITTS/NATUREPL.COM (23); BRANDON COLE (23 INSET)Not Always RecognizedIf you saw a jelly baby, or larva,you might not know it’s a jelly.Baby jellies change shape severaltimes as they grow. The typicaljellyfish, with a bell and trailingtentacles, is how they look whenthey are grown up.The spotted jelly(left) is a “gardener.”It grows tiny plantsunder its skin! Theplants make food thatthe jelly absorbs.The jelly at right has afishy fan club—smallfish that stick closeto it to stay safe fromenemies.22 23