While the vehicle dives deep into the cold undersea darkness, scientists sit comfortably aboard a ship on the sea surface, controlling the ROV movements remotely and watching its video feed on a bank of screens.

There’s a huge amount to be learned: not only which (and how many) jellies exist, but just as important, what they’re all doing down there. Edith Widder, a marine scientist at the Harbor Branch Oceanographic Institution in Florida, is developing “Eye in the Sea,” a supersensitive camera that will sit on the seafloor and watch bioluminescent organisms light up in their natural environment. It was years before scientists realized that polyps, small organisms that grow on surfaces such as rocks, are actually the immature form of free-swimming jellies. Jellyfish, also known as jellies, are fascinating animals that spend their lives floating in the oceans.

They’ll officially describe them, Raskoff says, just as soon as they discover something else: some spare time. A male sea-firefly ( Vargula hilgendorfii) will squirt out a bright dot of light, zip upward, and then squirt another and another, essentially drawing an arrow that points out his whereabouts. A really fun decorative addition to any room and way more exciting than a goldfish, with no feeding! As it turns out, they are a dominant form of life in the ocean, far more abundant than previously realized. Traditionally, biologists distinguished and classified jellies strictly according to physical shape: the number of tentacles, or a certain shape of the stomach.

It looked just plain bizarre: bulbous, dusky red, and huge, nearly one meter (about three feet) in diameter, with several fleshy arms instead of tentacles, like a balloon with greedy fingers. Humans can also be stung by jellyfish which can result in mild symptoms such as pain and blistering, to more serious symptoms including whole-body illness. And Monterey Bay, one of the best-explored deep-sea regions, represents only the smallest slice of the total.This light is used primarily as a form of communication between animals and can be used for defense, offense, and intraspecific communication. Meanwhile, the old web, thick with organic material, falls toward the seafloor and becomes a free lunch for another animal below. When something touches a jellyfish these nematocysts shoot out and can penetrate the skin of the animal. The viperfish ( Chauliodus sloani) dangles a luminescent lure in front of its mouth and then snaps up any creature that dares to investigate. Their membership consists of species from widely divergent taxonomic groups, including true jellyfish from the phylum Cnidaria, comb jellies from the phylum Ctenophora, sea snails and sea slugs from the phylum Mollusca (most mollusks, such as the familiar, hard-bodied clams and mussels, are not jellies), and a small group from the phylum Chordata (which mostly includes non-gelatinous animals such as birds, reptiles, and people).

To see the animal life, gelatinous or otherwise, that thrives at greater depths, a submersible vehicle like the ones used by scientists in Monterey Bay comes equipped with powerful lights. Some biologists have speculated that jelly populations thrive as increasing numbers of shrimps, fishes, and squids are harvested from the oceans, leaving behind vast amounts of uneaten small prey.Standing 24cm tall, the rounded tank holds two amazingly lifelike jellyfish which swim and glide around.