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Today, it’s time to learn all about jellyfish. Despite their name, it’s important to know that jellyfish are not fish at all. In fact, to avoid confusion, they are sometime called sea jellies, or even just jellies.
Characteristics of Jellyfish:
Jellyfish are invertebrates, which means they don’t have bones. In fact, they have no brain, no heart or other organs like lungs or gills.
Jellyfish obtain the oxygen they need through a process called diffusion whereby they absorb oxygen directly through their thin, permeable body walls from the surrounding water, allowing them to survive without specialized respiratory organs.
Made up mostly of water, these creatures are characterized by their gelatinous, umbrella-shaped bells and trailing tentacles.
Jellyfish are free-swimming which means they don't really have a permanent hime. They often drift with ocean currents, traveling through oceans, seas, and bays.
Jellyfish play an important role in the ocean. They function both as predators and prey. They feed on small fish, plankton, and even other jellyfish, using their tentacles to ensnare and immobilize their prey with toxins. At the same time, they are an essential food source for various larger species, such as turtles and certain fishes.
The main part of a jellyfish is the bell, which looks like an umbrella. This bell moves by pulsating, pushing water from underneath to help the jellyfish swim or float. The surface of the bell can be smooth or have frilly edges depending on the type of jellyfish, and it holds their basic digestive and nervous systems.
Hanging from the bell are the jellyfish's tentacles, which they use to defend themselves and catch food. These tentacles have thousands of tiny stinging cells called nematocysts. Each cell has a small dart that can shoot out and deliver venom, which paralyzes or kills small sea creatures. Jellyfish can stretch out or pull in their tentacles when they need to.
Below the bell are the oral arms, which are thicker and look a bit like the tentacles but have a different job. They help move the food caught by the tentacles to the jellyfish’s mouth.
Types of Jellyfish:
Jellyfish are found in every ocean in the world, and they come in a variety of shapes, sizes, and colors.
Moon Jellyfish are one of the most common and recognizable jellyfish species, the Moon Jellyfish is known for its translucent, saucer-shaped bell which can be up to 40 centimeters in diameter. These jellyfish typically inhabit temperate and tropical oceans around the world and are often seen in large numbers. Their diet mainly consists of plankton and small fish.
The Lion's Mane Jellyfish holds the title for the largest jellyfish. The Lion's Mane can have a bell diameter of over 2 meters and tentacles that extend up to 30 meters or more. It is found in the cold,waters of the Arctic, Northern Atlantic, and North Pacific Oceans. The tentacles are grouped in eight clusters, each cluster containing up to 150 tentacles, lined with nematocysts to capture prey.
Known for being one of the most venomous marine creatures, the Box Jellyfish has a cube-shaped bell and can grow up to 20 centimeters along each side. Its tentacles, which can reach up to 3 meters in length, are covered with potent venom that can be fatal to humans. Box Jellyfish are primarily found in the waters of the Pacific and Indian Oceans, particularly around northern Australia and throughout Southeast Asia.
Cannonball Jellyfish are named for their round, cannonball-like shape. This jellyfish is common in the coastal waters of the Southeastern United States and into the Caribbean. The bell of the Cannonball Jellyfish can reach up to 25 centimeters in diameter, and while its sting is not generally harmful to humans, it can stun small fish.
These are just a few examples of the diverse array of jellyfish species found in oceans around the world.
Jellyfish Life Cycle:
One super-interesting thing about jellyfish is their life cycles, which include several unique stages.
The cycle starts when a female jellyfish releases eggs into the water. These eggs get fertilized by sperm released from a male jellyfish. The fertilized eggs soon develop into larvae known as planulae. These tiny, free-swimming offspring drift with the ocean currents until they find a suitable place to settle down.
Once the planulae find a good spot, like a sea floor or a rock, they attach themselves and transform into polyps. Polyps look like tiny sea anemones or pieces of coral and can stay in this form for years. During this time, they feed on small floating organisms by catching them with their tentacles.
Next, during a process called strobilation, the polyp reproduces asexually. It splits up to create stack-like segments called ephyrae on top, which are young jellyfish.