Ctenophores come in all shapes and sizes, but they share a common method of locomotion: eight rows of cilia, beating in mesmerizing synchrony. These bioluminescent blue-green “combs” light up coastal shores at night—as well as the depths of the twilight zone, where a number of species have yet to be formally described. In images, ctenophore combs sometimes appear rainbow-colored, but this prism effect is actually the product of light refraction rather than bioluminescence.
Despite their clear, jelly-like appearance and simple nervous system, ctenophores are not related to jellyfish. Ranging from the egg-like Pleurobrachia to the ribbony Cestum veneris (also known as Venus’ girdle), ctenophores’ shape might have something to do with their hunting strategy: some stay still, with their tentacles hanging down to trap passing zooplankton in a sticky web; others engulf tasty larvae with wing-like lobes.
Almost every type of ctenophore eats with a little help from its friend the colloblast. These mushroom-shaped cells in the tentacles secrete a sticky substance to help reel in prey. (This strategy is similar to a jellyfish sting, but not at all venomous.) Some species, like Beroe, forgo the tentacles for “macrocilia” in their large mouths to usher in and bite off bits of prey—usually other ctenophores—while Ocyropsis traps prey in its lobes and stuffs it in its its mouth.
In general, coastal comb jellies tend to be tough enough to endure punishing tidal action, while open-ocean species are so fragile, they are hard to capture intact. Aside from their bioluminescent lights, most ctenophores are clear. One notable exception is the deep-sea species Bathocyroe, whose deep red stomach disguises its bioluminescent dinner. (Red light doesn’t penetrate the twilight zone, so it appears black.) Although many species have yet to be described, scientists think that a majority of ctenophores live in the twilight zone.
Comb jellies play an important role in regulating the marine ecosystem. They eat lots of fish and shellfish larvae, but in turn, they provide food for fish, jellyfish, and leatherback sea turtles. They also consume large amounts of copepods, which prey on phytoplankton that grow on the ocean surface in the presence of sunlight and carbon dioxide. Though the so-called “jelly web” is far from understood, researchers are investigating how ctenophores and other gelatinous zooplankton recycle nutrients and transport carbon through the ocean.
|Scientific Name||Over 100 species—not all have been described|
|Other Names||Comb jellies, sea walnuts, sea gooseberries, Venus’ girdles|
|Size||1 millimeter to 1.5 meters (nearly 5 feet)|
|Discovery||Johann Friedrich Gustav von Eschscholtz, 1829|
|Eats what?||Smaller species feed on “marine snow” detritus, fish larvae, copepods; larger species eat smaller zooplankton, crustaceans, jellyfish, salps, or other ctenophores|
|Eats how?||Most species use sticky tentacles to reel in prey; non-tentacled species use lobes or cilia to usher prey into mouth and take bites|
|Is eaten by?||Fish, jellyfish, sea turtles|
|Bioluminescence||Most species, except platyctenids and the cydippid genus Pleurobrachia|