Orange Atlantic or East Coast sea nettle. (Istockphoto )

Jellyfish are among the coolest-looking inhabitants of the sea. I have spent hours watching them during visits to the National Aquarium in Baltimore.

Although I love looking at jellyfish inside glass enclosures, running into them in the ocean is a different matter entirely.

There are hundreds of jellyfish species worldwide. Jellyfish don’t have hearts, bones or eyes. In fact, jellyfish aren’t even fish: They belong to a group of animals called invertebrates, which means they don’t have backbones. Because they aren’t in the fish family, scientists often refer to them as “jellies.”

Jellyfish feed on small fish, shrimp, zooplankton and other jellyfish. They catch prey using tiny barbed stingers on their tentacles called nematocysts. When an unsuspecting creature brushes against a nematocyst, venom is injected into the animal, stunning or killing it. The jellyfish then pulls the prey into its mouth.

Jellyfish also use nematocysts for defense. If you come in contact with a jellyfish, not only will the nematocysts inject venom into your flesh, but tentacles might break off and get stuck to your skin. Because nematocysts do not always “fire” on contact, you could be stung again if you don’t carefully remove the remaining stingers. A jellyfish can sting you even if it’s dead, so you should never use your bare hands to pick up a jellyfish that you find on the beach.

First aid for jellyfish stings can be divided into four steps. You should ask for help from a grown-up. (You might have heard that peeing on jellyfish stings is a good thing to do. It isn’t!)

●Remove the tentacles. Gently rinse the area with lots of seawater. Never use fresh water, because it can trigger the stingers to release venom. Don’t touch the tentacles with your bare hands.

●Deactivate the nematocysts. If you search the Internet, you will find conflicting advice about this step. That is because the best method to deactivate nematocysts depends on the type of jellyfish involved.

For example, one method for deactivating nematocysts is to soak the area in vinegar. The most common jellyfish along the Atlantic coast and in the Chesapeake Bay are sea nettles. Although vinegar is effective for some types of sea nettles, it can trigger nematocysts to fire in others. A safer method for sea nettles is to apply a paste made of baking soda and seawater.

●Remove the nematocysts. Rubbing the area with a towel might cause nematocysts to release more venom. Instead, use a credit card to gently scrape off the stingers.

●Relieve pain and swelling. In the past, ice was recommended to lessen the pain from jellyfish stings. Newer research suggests that it’s more effective to soak the area in moderately hot water for 20 minutes. Of course, that might be impractical if you’re on a beach.

Ibuprofen or acetaminophen also can help with pain. Applying calamine lotion or steroid ointments can reduce itch.

Bonus fact: If you need more advice about jellyfish stings, a grown-up can call the national poison control help line at 800-222-1222.

— Howard J. Bennett

Rose Ann Soloway, a clinical toxicologist at the National Capital Poison Center, helped with this article.