True Jellies
True Jellies
Xander Wroblewski – Summer 2025 Education Intern
“Jellyfish” is a term that describes an array of soft-bodied animals found throughout the world’s waters, namely cnidarians (true jellies, box jellies, and siphonophores) and ctenophores (comb jellies). These gelatinous zooplankton are found in every ocean, from the surface to the seafloor. They are one of the oldest animal lineages on the planet, with fossils found from organisms that lived 580 million years ago. Jellyfish can be seen year-round in North Carolina and are found often washed up on beaches after periods of sustained onshore wind.
To view a live-updating map of jellyfish wash-ups on Bald Head Island, click this iNaturalist project link [https://www.inaturalist.org/projects/bhic-jellyfish-wash-up-map]. This map displays real-time sightings of washed-up jellies on Bald Head Island, allowing visitors to know which beach accesses may have harmful animals onshore. iNaturalist is a community science photo ID app: you can upload pictures of an animal or plant, the app itself or experts in the field will identify it for data collection purposes. Please upload any jellyfish found on Bald Head to iNaturalist, so they will automatically appear in the wash-up map for other visitors.
Anatomy
True jellyfish fall under the class “Scyphozoa” and have a jellyfish’s standard appearance: a rounded bell with arms and tentacles hanging underneath. The bell is simple and made of two tissue layers (the outer skin lining and the stomach lining) separated by mesoglea jelly in between, lacking organs entirely. Jellies have one stomach cavity connected to feeding canals with one entrance that is both a mouth and an anus. True jellies contract their bells to propel themselves forward, though many rely purely on currents for movement. The bell is dotted with up to 8 rhopalium sensory clusters and ringed with dangling appendages: oral arms and tentacles. Typically, tentacles are covered in stinging cells called cnidocytes– cnidocytes contain a barbed harpoon coated in venom which is injected into anything that comes in contact with it. Venom can be used to paralyze or kill prey, as well as to deter predators. These tentacles pass the prey to the frilly oral arms, which move prey into the mouth.
Observed True Jelly Species on BHI
Cannonball jellyfish (also called cabbagehead jellyfish) are by far the most common jelly observed on Bald Head Island– they alone make up to 16% of the total biomass found on North Carolina beaches. They amass offshore in spring to reproduce, often getting blown to shore in early summer. Cannonball jellies can reach up to 10 inches across and have a firm, clear or brown ball-shaped bell with a chocolate-colored ring at the rim. This species lacks tentacles and thus can not sting people, instead they have a mop of fused oral arms they use to consume zooplankton, particularly fish larva. Cannonballs can be found in small groups or large colonies, sometimes with portly spider crabs residing in their bell. The two species have a symbiotic relationship: spider crabs ride inside the jelly’s bell and eat leftover food scraps, preventing the cannonball from getting infections. Cannonballs make up the majority of the leatherback sea turtle’s diet, and are often caught for use in jellyfish soup.
Mushroom jellyfish may appear similar to a cannonball jelly, but there are a few key differences between the two species. Mushroom jellies are much larger at about 20 inches across and much flatter in shape. They are also softer in texture, lack brown bands on the bell, and have 8 separated oral arms as opposed to the cannonball’s one large mop. Mushroom jellyfish are usually cream with yellow-brown markings on the oral arms, but can be slightly blue, pink, green, or brown. Mushroom jellies lack tentacles, but retain their venomous cnidocytes on the inside of the bell tissue; they have a mild sting that may not be felt by humans. These jellyfish eat small zooplankton, particularly crustacean larvae.
Atlantic sea nettles are the second largest jellyfish in North Carolina, reaching up to 16 inches in diameter with 40 2-foot-long tentacles and four frilly oral arms. Atlantic sea nettles are transparent with white or red dots running in belts or stripes around the bell, but are often tinted pale yellow or pink. They are solitary, often seen in the open ocean during summer months feeding on other jellies, amphipods, fish, and mosquito larvae. In turn, Atlantic sea nettles are consumed by sea turtles and ocean sunfish. Sea nettles have a moderate sting and are the most common jellyfish reported for stinging beach-goers in the Carolinas: if a sea nettle is sighted it is best to avoid entering the water, as they can cause a painful rash.
The bay nettle was declared a distinct species from the Atlantic sea nettle in 2017 due to genetic, morphological, and behavioral differences recognized by the National Aquarium in Baltimore, MA. Bay nettles are typically found in estuarine harbor waters, have a maximum width of 4 inches, and have longer oral arms. Bay nettles sport up to 24 tentacles used to prey on comb jellies and small crustacean larvae. Bay nettle planula young often settle on oyster shells to form polyps, making adult bay nettles frequent sights around oyster reefs. Their sting is similar to the Atlantic sea nettle’s, call a medical professional if symptoms are severe.
Moon jellies are one of the most well-known jellyfish species due to their popularity in aquarium exhibits. They get their name from their natural tendency to swim in extensive surface blooms at night; these blooms are so thick that they act as a wall, making movement through the swarm difficult. Southern moon jellyfish reach 8 inches in diameter with the majority of the body consisting of a blue or white-tinted circular bell. The bell is ringed with short, extremely thin tentacles responsible for catching small plankton and coating them in mucus. These tentacles do not have a sting strong enough for humans to feel, leading to moon jellyfish commonly being housed in touch tanks. Moon jellies are easily recognized by their four horseshoe-shaped gonads surrounding their mouth. They do not have strong bell convulsions and rely on water currents for movement. Moon jellies are naturally found in shallow water, often in hypoxic, heavily polluted conditions where they dominate all other lifeforms due to their ability to exclude plastics and toxins from entering their body.
The lion’s mane jellyfish is sometimes considered the longest individual animal on the planet, with a bell that can reach a maximum of 7 feet across and tentacles that can stretch up to 120 feet long, equivalent to 3 school buses. Despite their immense capacity for growth, most lion’s mane jellyfish are around 12 inches across and a few feet long. They have a bright orange or red bell divided into 8 lobes, each lobe housing a group of 70-150 outer tentacles densely packed with cnidocyte stinging cells. Inside these outer tentacles are up to 1200 sticky feeding tentacles surrounding the mouth that have fewer cnidocytes. These jellyfish are generally found in solitude within the uppermost 60 feet of cold open ocean waters. They avidly hunt fish and jellies, and are considered top predators when adults. Lion’s mane jellyfish have a very painful sting described as a warming sensation that begins to pulse, leading to reddened skin and swelling. Call a medical professional if you are stung by a lion’s mane jelly, especially if you are stung by many tentacles.
Dwarf lion’s mane jellyfish lack the punch that their larger relatives give but can still produce a moderately painful sting with similar symptoms. These jellyfish are significantly smaller, capping at about 2 inches across. They are easily distinguished by their bright pink bells with orange-red stomach tissues designed for digesting small gelatinous zooplankton. Dwarf lion’s manes are frequently seen in cold, open-water estuaries, locally called “winter jellyfish” as they congregate around North Carolina in winter to avoid the warm Gulf Stream.
Turritopsis nutricula is closely related to the deep-sea Turritopsis jellyfish commonly referred to as the immortal jelly, and as such, both species have similar life cycle-altering characteristics. Turritopsis jellies can restart their life cycle at any stage of development: their cells undergo rapid transformation from an adult medusa to a larval polyp when they are injured or stressed. Theoretically, this ability is unlimited, and can extend the lifespan of the organism indefinitely, though individual jellies often succumb to disease or predation by larger jellyfish. Genetic analysis of Turritopsis DNA is currently underway to minimize the health risks associated with aging. Although they have incredible adaptations, these jellies are very small, about ¼ inch across with 80 hair-like tentacles used for catching microscopic plankton. Their medusa form is transparent with a bright red stomach, while their polyp form is extensively branched. Turritopsis jellyfish are believed to have originated in the Pacific ocean but are now found world-wide after they entered the interconnected conveyor belt between ocean basins.
Sting information
Jellyfish do not intend to sting humans, most stings result from accidental contact with the jelly’s tentacles. Jellies in North Carolina are not lethal, but can still deliver a moderate to severe sting. Jellyfish tentacles can sting after the animal has died, and even if the tentacle is separated from the body. It is easier to prevent a sting than to treat it: consider viewing the live-updating jellyfish map [https://www.inaturalist.org/projects/bhic-jellyfish-wash-up-map] for recent sightings, check the water for jellyfish before entering, and never swim alone.
If you are stung, the most important thing to do is stay calm – get out of the water and call for help. Remove embedded tentacles with a pair of tweezers or gloved hands. Do not use bare hands to remove tentacles, as they will sting your fingers. Do NOT urinate or put freshwater on a jellyfish sting, as it will cause the stinging cells to fire again and release more venom.
If you have been stung by any species of jellyfish, including a man o’ war, wash the affected area with seawater. Then, rinse the skin with vinegar to deactivate stinging cells. Soak the wound with hot (115F) water or apply a heat pack for 20-40 minutes to ease pain. After, consider applying a cold pack for 20 minutes to reduce swelling. Symptoms will vary by species, but may range from minor itching and redness to severe skin rashes, cardiac dysfunction, or respiratory issues. If the affected area is still painful after treatment or if you are stung by a box jelly or man o’ war, contact a healthcare professional.
References:
https://docs.google.com/document/d/10mdAKINFXDzUjTuhrx1IQ4kkruJwkJQw2g5w9_malts/edit?usp=sharing
