7 Facts About Jellyfish + Photos of Caribbean Jellyfish

They’re neither the most primitive beings nor are there killer jellyfish; there are many legends surrounding these animals and facts about jellyfish that we don’t know. We are mesmerized by them when we dive, our hearts sink when we find them as fluorescent decor in some upscale restaurant tanks, and most of us run off the beach at the first sign of their presence.

But the truth is, we call animals jellyfish when they aren’t, we think they attack when they never do, and for most people, they remain a big mystery. Today, we’re going to clear that up with this collection of facts about jellyfish.

1. What Are Jellyfish?

Jellyfish, although many people mistakenly think they are fish (for some reason), actually aren’t. These fascinating marine animals belong to the group called Cnidarians, which also includes corals, sea anemones, and the dangerous Portuguese man o’ war—though it is not a true jellyfish.

Cnidarians are tiny animals that either form colonies, like corals, or live as solitary individuals. When the animal is attached, it is called a polyp; when it is detached and swims freely, it is called a jellyfish.

Some of the most distinctive features of jellyfish and other cnidarians include their bell-shaped bodies, a single central opening that serves as both mouth and anus, and several tentacles surrounding the mouth used for capturing prey and defense.

These tentacles are equipped with cells containing a more or less stinging liquid (nematocysts), which is one of the main reasons jellyfish are both feared and admired in the marine world. But here’s an important note about jellyfish: they don’t actively attack with venom; instead, if their tentacles brush against your skin, the nematocysts break open, releasing the venom.

Cnidarians are divided into three classes: Hydrozoa, Scyphozoa (true jellyfish), and Anthozoa (which includes sea anemones).

We already know about sea anemones from the article “30 Facts About Sea Anemones You Need to Know” Now, our goal is to differentiate which animals are jellyfish and which are not, because it can be tricky.

2. Hydroids, Hydromedusae, and Siphonophores resemble jellyfish, but they are not jellyfish

Hydroids (Class Hydrozoa, Order Hydroida) In these animals, the polyps are usually colonial and attached to a common structure or branched skeleton that grows in feather-like or fern-like patterns. They have a stage that resembles a “jellyfish,” and indeed, they look almost identical to jellyfish, with one key difference: their bell has a “velum,” a thin membrane that folds inward, forming a kind of shelf or inner rim at the bottom of the bell. During this typically short period, they are referred to as hydromedusae.

Siphonophores (Class Hydrozoa, Order Siphonophora)

The famous Portuguese Man o’ War is not actually a jellyfish but a colony of polyps.

These marine creatures are complex floating colonies that use a gas-filled float to stay buoyant. This float not only allows them to drift across the ocean but also helps regulate their depth in the water depending on the gas inside.

They move by pulsing swimming bells that expel gas for propulsion and are located just below the float. This mechanism enables them to maneuver efficiently through open waters.

Their sting can be quite severe, especially in species that drift in open waters.

3. True Jellyfish and Box Jellyfish

3.1. True Jellyfish (Class Scyphozoa)

Jellyfish are fascinating and enigmatic creatures of the marine world. When discussing jellyfish, it’s essential to highlight their diversity and uniqueness. True jellyfish belong to the Class Scyphozoa, and their anatomy is as interesting as it is varied.

Structure and Anatomy of Jellyfish

Jellyfish have a unique body structure, with a prominent bell that varies in shape. If compared to dishes, they can range from “flat plates” to large bowls. In jellyfish anatomy, their tentacles play a crucial role. Hanging from the edge of the bell, these tentacles are armed with stinging nematocysts, used for both capturing prey and defense. Depending on the species, the number and length of these tentacles can vary greatly.

The jellyfish’s mouth is located at the end of a feeding tube extending from the center of the bell’s underside. In some species, this tube is surrounded by four oral arms (named so because they are near the mouth) that dangle.

Another interesting fact about jellyfish is that, despite their biological complexity, they have no brain, heart, or bones. Instead, they possess a simple nervous system that detects light, vibrations, and chemicals in the water. Jellyfish are made up of 95% water.

Jellyfish lack a bony skeleton like other animals; instead, they have a hydrostatic skeleton composed of fluids and circular muscles in their bells. This system allows them to propel themselves by contracting their muscles and expelling water in the opposite direction of their movement. This method of propulsion is efficient in calm seas, but in stronger currents, jellyfish simply drift with the flow.

This simplicity makes them an evolutionary mystery and a fascinating subject for marine biologists.

3.2. Box Jellyfish (Class Scyphozoa, Subclass Cubomedusae)

Box jellyfish, scientifically classified under the class Scyphozoa and subclass Cubomedusae, are among the most fascinating and dangerous jellyfish species.

Structure and Anatomy of Box Jellyfish

Box jellyfish have a unique anatomy, starting with their distinctive cubic bell. This box-like shape, with its four square sides, sets them apart from other jellyfish. Their appearance is not only distinctive in shape but also in rigidity, as their bell is more solid compared to common jellyfish.

One of the most interesting facts about box jellyfish is their advanced visual capability. These jellyfish have sophisticated vision, which is rare among jellyfish. With 24 eyes spread across the four sides of their bell, they have a 360-degree field of view, allowing them to detect prey and potential threats with great efficiency. They are also extremely fast, capable of moving up to six meters per minute.

Tentacles of Box Jellyfish

Each of the four corners of the box jellyfish’s bell has one or more tentacles filled with stinging nematocysts. Unlike other jellyfish, these tentacles do not hang from the edge of the bell but are strategically placed at the corners, giving them a unique and effective appearance for hunting.

Regarding their life cycle, box jellyfish undergo a polyp stage and a medusa stage, similar to other species, but their cubic shape is unique to this type of jellyfish.

The sting of box jellyfish is known to be extremely painful and, in some cases, fatal. For this reason, it’s crucial to exercise caution if you are in waters where these jellyfish are found.

4. 7 Fun Facts About Jellyfish

1. Ancient History

Jellyfish are marine creatures that have existed for over 600 million years, making them some of the oldest beings on the planet. Despite lacking bones, scientists have traced their existence through “soft fossils,” which show impressions left in rocks. This data reveals that jellyfish have survived through mass extinction events, including those that wiped out the dinosaurs.

1. Diversity of Jellyfish Species Number of Species.

It is estimated that there could be up to 300,000 species of jellyfish, though only over 2,000 have been discovered and described. Each species has unique characteristics. For example, the largest jellyfish, like the lion’s mane jellyfish, can grow up to two meters wide with tentacles extending up to 36 meters long. In contrast, small jellyfish, like the Irukandji, measure only one or two centimeters. This diversity in size and shape makes jellyfish fascinating and varied.

1. Jellyfish Lifespan and Other Fun Facts

The lifespan of jellyfish varies greatly by species. Some live only a few days, while others can live much longer. An interesting fact is that the immortal jellyfish, scientifically known as Turritopsis dohrnii, can reverse its life cycle. If it faces survival difficulties, it can transform into a cyst, return to the ocean floor, and restart its life cycle from the beginning. It then develops into a polyp and clones itself to form a colony. Once the colony matures, it starts producing adult jellyfish again.

1. Bioluminescence.

A Natural Spectacle Among the fun facts about jellyfish is their ability to produce light through bioluminescence. This ability not only allows them to glow in the dark ocean but also helps them attract prey, communicate with each other, or camouflage from predators. Photos of bioluminescent jellyfish display truly spectacular light shows.

1. Breathing and Oxygen Absorption

Despite lacking gills, jellyfish can absorb oxygen directly through their skin, allowing them to survive at various ocean depths. Some jellyfish species even have sensors that detect light, helping them navigate their aquatic habitat.

1. Role in the Ecosystem

Jellyfish are effective predators that feed on fish, shrimp, crabs, and small plants. They use their stinging cells, called nematocysts, to paralyze their prey before consuming it. At the same time, jellyfish are an important food source for many marine creatures, such as sea turtles, tuna, swordfish, and sharks.

1. Myths and Realities About Jellyfish

One widely spread myth about jellyfish is that urine can relieve the pain from their stings. However, this is false and can actually worsen the situation by activating more nematocysts. The proper way to treat a sting is to rinse the affected area with vinegar and apply cold compresses to reduce pain and inflammation.

5. Caribbean Jellyfish Photos

Divers often encounter a wide variety of these animals during their dives, and knowing a few facts about jellyfish them can be essential for both safety and enjoying these fascinating marine creatures. Below is a detailed list of some of the most common jellyfish species you might come across on your underwater adventures in the Caribbean.

Warty Jellyfish (Pelagia noctiluca)

Belonging to the class Scyphozoa, this jellyfish measures between ¾ and 4 inches (2-10 cm). It is identified by its dome covered in wart-like structures with nematocysts, eight contractile tentacles, and four frilled oral arms. It is translucent with pink, purple, yellow, or brown tones and is bioluminescent at night.
Fun Fact about Warty Jellyfish: This species is known for its bioluminescence and painful stings.

Blue Jellyfish (Phyllorhiza punctata)

Size: Between 6 and 8 inches (15-20 cm).
It is blue to blue-green with white spots, has a thick, granular dome, and its oral arms have long, club-shaped appendages with hanging filaments.
Fun Fact about Blue Jellyfish: Despite their size and appearance, these jellyfish have relatively low toxicity, making them less dangerous for divers.

Moon Jellyfish (Aurelia aurita)

Size: Between 6 and 8 inches (15-20 cm).
It has a saucer-shaped dome with numerous short, fringe-like tentacles around the edge. The reproductive organs, shaped like a clover, are visible through the translucent dome.
Jellyfish Anatomy: Slightly toxic; it can cause mild itching and rashes. It is one of the most well-known and studied jellyfish.

Cannonball Jellyfish (Stomolophus meleagris)

Size: 4 – 7¼ inches (10-18 cm).
It has a bulb-shaped dome with short, bifurcated oral arms around a robust feeding tube.
Fun Fact about Cannonball Jellyfish: They do not sting. Although not among the largest, its robust structure makes it notable in its habitat.

Spicy Cauliflower Jellyfish (Drymonema dalmatinum)

Size: 1½ – 3 feet (0.6-1 meter).
It has a smooth, saucer-shaped dome with lobes around the edge. The tentacles are short and range in color from lavender to purple.
Jellyfish Tentacles: Its short and powerful tentacles are particularly dangerous, highly toxic, and its sting requires immediate treatment.

Mangrove Upside-Down Jellyfish (Cassiopea xamachana)

Size: Between 6 and 7 inches (15-18 cm). It has a flattened, disc-shaped dome with clustered and branched oral arms.
Jellyfish Species: This jellyfish is unique for its inverted resting behavior, which facilitates the growth of symbiotic algae on its body

Sea Wasp (Carybdea alata)

Size: Between 2 and 3¼ inches (5-8 cm).
It is a box jellyfish with a rectangular, translucent dome and reaches a height of between 2 and 3¼ inches. It is easily identifiable by the tentacles hanging from each of the four corners of the dome.
Facts about Sea Wasp Jellyfish: These jellyfish are attracted to light at night, making them common in shallow reef areas.

In summary, all these facts about jellyfish reveal a fascinating diversity and complexity. Understanding their true characteristics and distinctions helps us appreciate their role in the ecosystem and debunk many misconceptions. And by looking at the photos of Caribbean jellyfish, we understand that a dive is well worth an encounter with them. Want to see them for yourself? Contact us.