There are about 1000-1500 known types of jellyfish in oceans worldwide.
Moon Jellyfish: Aurelia aurita
The Moon Jelly is the most famous species of jellyfish and is often kept and bred in captivity. This is the type of jellies most commonly seen in public aquariums and sold at Jellyfish Art. They are transparent and easily distinguished by four pink horseshoe markings. Their size varies between 1 and 8 inches and in diameter. The sting of the moon jellyfish is venomous but only has no effect on people. Because of their translucent bodies, moon jellies will glow with whatever color of light is shone on them.
Man-of-War Jellyfish: Physalia physalis
Also known as the Portuguese man-of-war, Blue Bottle and Blue Bubble, this jelly has a purple-blue tint and is found in warm ocean waters throughout the world. With an approximate length of 12 inches and width of 5 inches, a Man-of-War can grow tentacles up to 50 meters long, although 10 meters is the average. These jellies are covered with venom-filled nematocysts used to paralyze and kill small fish and other creatures. For humans, a sting from this species can be excruciatingly painful but rarely fatal.
Lion's Mane Jellyfish: Cyanea capillata
The Lion's Mane Jellyfish holds the record for longest animal in the world because of its extremely long tentacles. These jellies live in the cold waters of the Arctic Ocean and Northern Pacific Ocean. They rarely descend below 42 degrees latitude and are never found in the southern hemisphere. The Lion's Mane, like most other species of jellyfish, is carnivorous and feeds on zooplankton, small fish, and ctenophores. The Lion's Mane jellyfish also feeds on other jellyfish like Moon Jellies. Predators of the Lion's Mane Jellyfish include seabirds, larger fish, other jellyfish species and sea turtles. Despite their dangerous name, this jelly is relatively harmless to humans – their sting only causes an itchy rash and mild burning sensation.
Freshwater Jellyfish: Craspedacusta sowerbyi
Almost all of the world's species of jellyfish live in salt water, but there are a few fresh water jellies like Craspedacusta sowerbyi. There are significant differences between this freshwater jellyfish and its marine counterpart. The freshwater jelly has a structure called a velum on the ventral surface. This membranous structure extends inward from the circular edge of the jellyfish's bell. The jelly originated from the Amazonian forests of South America and are abundant all over the world. The freshwater jelly can be found in freshwater lakes, rivers,algae-filled ponds, reservoirs, man-made impoundments, water-filled gravel pits and rock quarries. These jellies prefer standing water and do not like tides or currents. The body of the freshwater jellyfish is transparent with a white or green tinge. Unlike the marine jellyfish, the freshwater jellyfish's tentacles are not powerful enough to break into human skin, and so humans don't feel any sting from the freshwater jellyfish.
Atlantic Sea Nettle: Chrysaora quinquecirrha
This species is commonly found along the east coast of North America in the Atlantic Ocean. The Sea Nettle is semi-transparent and has small whitish dots and reddish-brown stripes. The sea nettle is saucer-like in shape with four oral arms attached to the underside of the mouth and a number of long tentacles. Unlike many species of jellyfish, who only feed on microscopic plankton and zooplankton, the sea nettle also eats a number of significantly larger preys, such as young minnows, bay anchovy eggs, worms and mosquito larvae. Although these are dangerous jellies, it is important to note that they do not "attack" humans but rather use the sting as a natural defense mechanism.
Upside Down Jelly: Cassiopea sp.
Upside Down Jellyfish in habit shallow waters around the world. This jellyfish looks less like an ordinary jellyfish and more like a sea anemone as it sits upside down on the bottom most of the time. This camouflage is what enables the jellyfish to survive well against predators. This jelly also hosts symbiotic algae within its tentacles, which provide nutrition to the jellyfish. These can be found on the bottom in huge numbers, making them look like a bed of flowers.
With around 1500 discovered species of jellyfish so far, scientists are covering more uncharted ocean territories and continuously discovering new species.