"Jellyfish are extremely simple organisms, characterized mainly by their undulating bells (which contain their stomachs) and their dangling, cnidocyte-spangled tentacles. Their nearly organless bodies consist of just three layers—the outer epidermis, the middle mesoglea, and the inner gastrodermis—and water makes up 95 to 98 percent of their total bulk, compared to about 60 percent for the average human being."
"Jellyfish are equipped with hydrostatic skeletons, an innovation that evolution hit on hundreds of millions of years ago. The bell of a jellyfish is a fluid-filled cavity surrounded by circular muscles; the jelly contracts its muscles, squirting water in the opposite direction from where it wishes to go."
"Jellies have evolved specialized structures called nematocysts. There are thousands of nematocysts in each of the thousands of cnidocytes on a jellyfish's tentacles. When stimulated, they build up pressure and explode, piercing the skin of the unfortunate victim and delivering thousands of tiny doses of venom."
"Weirdly, box jellies are equipped with as many as two dozen eyes—not primitive, light-sensing patches of cells but true eyeballs composed of lenses, retinas and corneas. These eyes are paired around the circumference of their bells, one pointing upward, one pointing downward—giving some box jellies a 360-degree range of vision, the most sophisticated visual sensing apparatus in the animal kingdom. Of course, these eyes are used to detect prey and avoid predators, but their main function is to keep the box jelly properly oriented in the water"
There are four main groups of jellies. "Scyphozoans, or "true jellies," and cubozoans, or "box jellies," are the two classes of cnidarians comprising the classic jellyfish. There are also hydrozoans (most species of which never getting around to forming bells, instead remaining in polyp form) and staurozoans, or stalked jellyfish, which are attached to the sea floor."
So that's the skinny on jellies. Now for the fun part, the photos!
Lion's Mane jellyfish. The largest known type of jelly, the largest recorded specimen had a bell that was 7' in diameter and with tentacles that stretched for an amazing 120' !
Another shot of a Lion's Mane jelly.
Yet another shot of a Lion's Mane jellyfish.
One of the most colorful and spectacular jellies is the oddly named Flower Hat jelly. Found off the southern coast of Japan, this 6" wide jelly's sting is painful but not deadly.
This extremely rare Halitrephes maasi jellyfish was only recently found in deep Mexican waters. Its bioluminescence is only activated when a light shines on it. Otherwise it swims unnoticed in the dark.
Moon jellies are one of the most common of all jellyfish - and one of the most prolific. Huge blooms of them have clogged warmer ocean bays, causing problems for fishermen.
Sea nettle jellyfish. Different species of this widely distributed jelly can be found in the Atlantic (the more colorful types) or in the Pacific ocean. The bells are about a foot across, with tentacles as long as 30'. In this photo, juvenile fish swim inside the tentacles for protection from larger predators.
Here are two more types of Sea nettle jellyfish (above and below).
Here are two more photos of the wildly colorful and totally weird Flower Hat jellies. I think my initial reaction is probably pretty common "THAT'S a jellyfish?!"
I couldn't find an ID for this jelly but it's so cool looking I decided to include it. It could be a type of box jellyfish.
No positive ID here either but I think it may be a Blue Blubber jelly. No, I'm not making that name up and in fact Blue Blubbers are fairly common.
Not sure which jellies these are but loved the photo. They are clustered under a kelp forest.
Box jellyfish. This longer view shot gives you an idea of just how long a jelly's tentacles can be.
Compass jellyfish. These common visitors off the coast of Britain get their name from the distinct brown pattern on their bell - a radial pattern that resembles a compass. Bells are about a foot across and the tentacles pack a nasty sting.
Crown jellyfish. Crown jellyfish are able to make light through bioluminescence. When they are touched, their bells will light up. Otherwise, the bell of a crown jellyfish will look transparent when undisturbed. When they are attacked, crown jellyfish are able to startle, mislead, and distract their predators with the light that they produce. They may also use their bioluminescence to lure or dazzle their prey.
Fried Egg (Egg Yolk) jellyfish. Monterey Bay Aquarium says: "Like a large bird egg cracked and poured into the water, that three-foot, translucent bell is yolk-yellow at the center, with hundreds of tentacles clustered around the margin. The egg-yolk jelly is one of the larger species of jellies commonly found in Monterey Bay. This massive jelly usually drifts motionless or moves with gentle pulsing. Acting like an underwater spider web with a mild sting, an egg-yolk jelly captures other jellies that swim into its mass of tentacles."
Giant jellyfish (Stomolophus nomurai). From Wikipedia "Growing up to 6.6 ft in diameter and weighing up to 440 lb, Nomura's jellyfish reside primarily in the waters between China and Japan,. Population blooms appear to be increasing with frequency in the past 20 years. Possible reasons for the population increase include climate change and over-fishing (of predators)."
Another shot of the Giant jellyfish. The swimmer gives some perspective as to this jelly's monstrous size.
Unknown jellyfish species. I suspect it's a Compass jelly (look at the radiating lines at its top).
Golden jelly (Mastigias papua etpisoni). From National Geographic - "Found near the remote Pacific island of Palau, these jellies actually follow the sun's path. Solar rays nourish essential, algae-like organisms called zooxanthellae, which live symbiotically in the jellies’ tissues and provide their hosts with energy as a byproduct of their photosynthesis."
Unknown jellyfish. I love the speckling on the bell of this very pretty jelly.
Moon jellyfish. Although most commonly Moon jellies are translucent, they can actually be pink or blue as well. Here's a very pretty one.
Purple jellyfish. From Wikipedia - "This species is known in Europe as the mauve stinger. It is widely distributed in all warm and temperate waters of the world's oceans, including the Mediterranean Sea, Red Sea and Atlantic Ocean. It is also found in the Pacific Ocean, with sightings in warm waters off Hawaii, southern California and Mexico, as well as other Pacific locations.
Versuriga jellyfish. From EarthTouch news - "Versuriga jellies are part of the order Rhizostomae, a group of jellyfish with no tentacles at all. Instead, they have eight highly branched "oral arms" – masses of spongy tissue used for filter feeding. This jelly doesn't have one mouth, but rather many small ones, like some kind of ocean-dwelling hydra. The mouths sit along the lengths of the arms, and gobble up plankton as they swim by. If you look closely you'll see some juvenile slender yellowtail kingfish using the jelly for protection against the predatory trumpetfish lurking nearby.
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