Lion's Mane jellyfish (Cyanea capillata)

This jellyfish has a bell reaching up to eight feet in diameter, and tentacles longer than a blue whale - up to 200 feet long. Juveniles are pink, turning red as they mature, becoming brownish purple as adults. This jellyfish can cause severe stings, and there have been rare reports of fatalities to swimmers. In one of the Sherlock Holmes mysteries by Sir Arthur Conan Doyle, a lion's mane jellyfish is the killer. It is found from temperate waters to the Arctic.

West Coast sea nettle (Chrysaora fuscescens)

Very long tentacles characterize this Pacific Ocean jellyfish, which is tan with reddish hues. Its sting can be mildly harmful to humans, something like a bee sting. The sea nettle is an opportunistic feeder, eating other jellyfish, fishes and microscopic animals. It is eaten by sea turtles and ocean sunfish.

Moon jelly (Aurelia aurita)

Sometimes found in huge swarms, this billowing jelly is a transparent, milky white, with short, fine tentacles around the bell rim. It is found from the Arctic to Florida and Mexico, from Alaska to California. This is the jellyfish most commonly seen washed up on beaches. Its sting causes a rash that may itch for several hours.

Umbrella jellyfish (Eutonina indicans)

This beautiful small (up to about one inch) jellyfish looks like a miniature umbrella, and is so transparent that it is nearly invisible in the ocean. (Invisibilty is an excellent defense against predators when there is no place to hide.) It is a hydrozoan, which means that its offspring live in colonies as polyps and then bud into small adult-like animals before maturing. Umbrella jellyfish live in cool northern oceans around the world.

Elegant jellyfish (Tima formosa)

Appropriately named, these tiny, attractive jellyfish live about 200 to 300 feet down in the water column. Japanese relatives of the umbrella jellyfish, they also are hydrozoans. They are known to be plankton feeders, but little else has been discovered about them. They float in open waters, usually near shore.

East Coast sea nettle (Chrysaora quinquecirrha)

This stinging nettle is common in the Chesapeake from mid-summer through fall. Mildly toxic, it is often a nuisance on bathing beaches because, true to its name, the stinging cells in the tentacles can deliver a painful sting. It preys mainly on fish larvae, crabs, oysters, and other jellyfish.

Upside down jellyfish (Cassiopeia xamachana)

This lovely tropical jellyfish resembles lacy ruffles and lives upside down on the bottom of mangrove swamps. Algae (zooxanthellae) in its tissues provide food for it.

Leidy's comb jelly (Mnemiopsis leidyi)

About two inches wide, comb jellies range from Cape Cod to the Carolinas and are common in the Chesapeake Bay as far north as Baltimore. They have eight moving comb plates that move food toward the mouth. Marine labs use them to study bioluminescence and regeneration. Comb jellies are not true jellyfish. They have no stinging cells.