7 Types Of Jellyfish In Connecticut (How To Identify Them)

Types of Jellyfish in Connecticut
Fact Checked and Reviewed by: Mark Rhodes, Ph.D. - Wildlife Biologist
Dr. Mark Rhodes holds an MS in Fisheries and Wildlife along with a Ph.D. in Wildlife Ecology. He helps maintain our editorial standards of accuracy and quality. You can read more about Dr. Rhodes here.

Connecticut’s Long Island Sound is one of the most important natural resources in the state, both for its contributions to the economy from boating, fishing, and tourism, as well as its importance for breeding, nesting, and feeding a diverse number of plants and wildlife. Among the many critters that call this estuary home are several species of jellyfish.

So, what types of Jellyfish are native to Connecticut?

Connecticut’s waters are home to several jellyfish species, including true jellyfish and other gelatinous plankton. The most common species of true jellyfish include moon jellyfish, lion’s mane jellyfish, sea nettles, mauve stingers, crystal jellyfish, mushroom jellies, and cannonball jellies. Species of gelatinous plankton, commonly found in Long Island Sound include comb jellies and sea gooseberries. 

Below, we’ll take a closer look at these common types of jellyfish in Connecticut, as well as gelatinous plankton. We’ll also talk about how you can identify them and what time of year they are most commonly found in the waters of Long Island Sound.

Types Of True Jellyfish In Connecticut

There are several true jellyfish species commonly found in Connecticut. In addition to moon jellyfish, lion’s mane jellyfish, and sea nettles, you can also find mauve stingers, crystal jellyfish, mushroom jellies, and cannonball jellies.

Let’s learn how you can identify these quiet animals!

Moon Jellyfish

Moon jellyfish have a saucer shape and are translucent with either a white or pink color. They grow to a diameter of 10 inches and have a unique pattern on the top of their bell that resembles a four-leaf clover. The horseshoe shapes that make up this pattern are actually the moon jelly’s sex organs.

The moon jellyfish has hundreds of hair-like tentacles on the outer rim of its bell. You’re most likely to see these jellyfish in Long Island Sound during late spring. Moon jellyfish are only slightly venomous, meaning they’ll produce prickly sensations or mild burning if you are stung.

Lion’s Mane Jellyfish

There are two types of lion’s mane jellyfish found in Connecticut. As juveniles, they are typically pink. Then, they will turn either reddish brown or purple as they become adults.

While lion’s mane jellyfish can grow to a diameter of 8 feet long, those found in Connecticut are typically 6-12 inches in diameter. They are known for their unique oral arms, which are ruffled and give the jellyfish the appearance of a lion’s mane. In addition to their oral arms, these jellies have eight U-shaped groups of pale, white tentacles coming from the underside of their bell.

Lion’s mane jellyfish are very common in the area. While they are most common during the summer months, they can also be seen in the winter and spring. Lion’s mane jellyfish can sting, but they are only mildly toxic.

Sea Nettles

Sea nettles in Connecticut are often white in color and grow to a diameter of 10 inches. They have eight groups of 3-5 tentacles each and their tentacles are very deadly to crabs or small fish that they may eat.

Sea nettles are most common in Connecticut during the summer months, particularly because they prefer less salty water like that of estuaries. Interestingly, sea nettles have red or maroon-colored markings when they are found in areas with higher salinity. They are venomous and have a painful sting, but are not deadly to humans.

Mauve Stingers

Mauve stinger jellyfish are small, having a bell diameter of 2.3-3.5 inches. They get their name from their pink color, though they can also be yellow and they are easily identifiable by the warts that occur on the bell of the jellyfish. By contrast, many other jellies have a smoother bell.

Mauve stingers are typically oceanic, but it is possible for them to be washed into estuaries like Long Island Sound. They have eight solitary tentacles rather than tentacles that grow in groups and four oral arms. This type of jellyfish is venomous.

Crystal Jellyfish

Crystal jellyfish are almost transparent or pink and are shaped like an umbrella with long, thin tentacles. Their bells can grow up to 10 inches in diameter, but their most notable feature is the bluish-green bioluminescent glow that they give off when disturbed.

Crystal jellyfish spend most of their time offshore, so you’re not likely to encounter them on the beaches of Connecticut. However, they are most likely to come inland and be washed ashore during the fall and summer months.

Cannonball Jelly

Cannonball jellies have a diameter no bigger than 8 inches and belong to the class Rhizostomeae. Jellyfish belonging to this class do not have tentacles and instead have shorter, wider oral arms that have several mouth openings.

These jellyfish have a large, hemispherical bell that is white in color with chocolate brown stripes. Mushroom jellies are considered one of the least venomous jellyfish, which is beneficial because they may gather in large numbers during the summer and fall months, particularly in estuaries like Long Island Sound.

They are often considered pests by commercial fishermen, particularly because they can clog and damage nets. Plus, these jellies have to be sorted out so they slow down sorting times.

Mushroom Jelly

Like cannonball jellies, mushroom jellyfish do not have tentacles but instead have oral arms with mouth openings. While they are sometimes confused with the cannonball jellyfish, because of certain visual similarities, mushroom jellies can grow to more than twice the size of cannonball jellies and be as big as 20 inches in diameter.

Additionally, there are differences in the shape of the bell and its colors. Mushroom jellies are also white, but they have a flatter, softer bell. They also do not have the same brown bands that are found on the bell of cannonball jellies. Similar to cannonball jellyfish, though, they don’t pose a serious threat to humans.

Other Gelatinous Plankton Found In Connecticut

In addition to the true jellyfish mentioned above, there are two types other types of gelatinous plankton classified as jellyfish found in Connecticut, including comb jellies and sea gooseberries.

Comb Jellies

Comb jellyfish are also sometimes called sea walnuts. Unlike true jellyfish, these gelatinous creatures lack stinging cells and pose no threat to humans. You’re most likely to see them between May and December.

Comb jellyfish are smaller in size, with most growing to a diameter of 2-3 inches. They lose their tentacles as they mature, instead having two long lobes that are attached near the top of their bodies. Comb jellyfish have sticky cells on the inside of these lobes that they use to trap their prey like fly paper.

Sea Gooseberries

Sea gooseberries are also transparent, though they are more spherical. They are smaller than comb jellies and grow to just 3/4 of an inch long. These jellies get their name from the unique comb plates that make up the outside of their bell and help with locomotion. The comb plates grow in rows, giving sea gooseberries eight distinct sections of their body.

Sea gooseberries have two fringed tentacles that dangle from the body so they can catch food. These plankton are also iridescent and they have a glow underwater. You’ll only see these jellies in Long Island Sound during the winter months.

Final Word

Connecticut is home to many types of animals, including seven types of jellyfish, as well as two other gelatinous plankton that are referred to as jellies. With their various sizes, colors, and traits, it’s fairly easy to tell these jellyfish apart.

This is fortunate since some jellyfish found in Connecticut, like the lion’s mane jellyfish, are venomous to humans. That being said, most of the jellies that are venomous are only mildly toxic to humans who are stung. This means that while the sting of a jellyfish can produce some discomfort, it’s not likely to be deadly or dangerous.