Jellyfish

Weight and Size

The Lion’s Mane jellyfish can weigh up to 440 pounds (200 kg), about as heavy as a piano!

The smallest jellyfish species are barely visible to the human eye, measuring about 1 centimeter (10 millimeters) across!

The Australian Box Jellyfish can reach about 12 inches (30 cm) in diameter with tentacles stretching 10 feet (3 meters) long!

The average Moon jellyfish grows to about 10-16 inches (25-40 cm) in diameter, about the size of a dinner plate!

The Nomura’s jellyfish can grow to 6.6 feet (2 meters) in diameter and weigh up to 440 pounds (200 kg)!

The Barrel jellyfish can reach up to 35 inches (90 cm) in diameter and weigh as much as 77 pounds (35 kg)!

The Pink Meanie jellyfish has tentacles that can stretch up to 70 feet (21 meters), longer than a school bus!

The upside-down jellyfish usually grows to about 12 inches (30 cm) in diameter, similar to the size of a large pizza!

The Blue Blubber jellyfish typically reaches about 12 inches (30 cm) across and weighs about 5 pounds (2.3 kg)!

The Atolla jellyfish, which lives in deep ocean waters, is usually about 4–6 inches (10-15 cm) in diameter but can flash bright red light that can be seen from 100 feet (30 meters) away!

Names for Males, Females, and Babies

Most jellyfish species have separate male and female individuals, but some species can function as both male and female at different stages of their lifecycle!

Baby jellyfish are called “ephyra” when they first detach from the polyp and start swimming freely!

Before becoming free-swimming ephyra, jellyfish begin as tiny larvae called “planula” that attach to surfaces on the ocean floor!

The stationary stage of a jellyfish’s life is called a “polyp,” which looks more like a tiny sea anemone than a jellyfish!

When a jellyfish is fully grown, scientists call it a “medusa,” named after the snake-haired monster from Greek mythology because of its flowing tentacles!

When several jellyfish polyps are connected together, they form what scientists call a “colony” or “hydroid colony”!

Some jellyfish species release eggs and sperm into the water to reproduce, while others carry their developing larvae in special pouches on their bodies!

A jellyfish polyp can produce up to 45 baby jellyfish in a single spawning season!

Jellyfish eggs are microscopic and can number in the millions for a single adult jellyfish!

In some jellyfish species, the tiny planula larvae swim using tiny hair-like structures called cilia before finding a place to attach and grow!

A single jellyfish polyp can produce 10-15 ephyra (baby jellyfish), and some species can produce hundreds from one polyp!

Diet and Feeding Habits

Jellyfish are carnivores, meaning they eat other animals, primarily tiny zooplankton, fish eggs, and sometimes small fish!

Jellyfish don’t actively hunt – they drift with their tentacles extended, waiting for prey to swim into their stinging cells!

A large jellyfish can consume up to 600 tiny fish or about 35 copepods (tiny crustaceans) per day!

Jellyfish have no teeth, so they dissolve their food using enzymes before absorbing the nutrients through their body!

Some jellyfish, like the upside-down jellyfish, get nutrients from tiny algae that live inside their tissues in a mutually beneficial relationship!

Jellyfish have a single opening in their body that serves as both a mouth and an anus – food goes in and waste comes out through the same hole!

Box jellyfish are active hunters that can move quickly and chase prey, unlike most jellyfish that simply drift and wait!

The Lion’s Mane jellyfish eats over 100 different kinds of sea creatures, including other smaller jellyfish species!

Some jellyfish species can survive for weeks without food when necessary!

Moon jellyfish eat by collecting food on mucus that covers their bodies, then moving the mucus to their mouths using tiny hair-like structures!

Physical Characteristics

A jellyfish’s body has three main parts: the bell (or umbrella), oral arms, and tentacles!

The jellyfish’s mouth is located in the center of its underside and is surrounded by oral arms that help guide food into it!

Jellyfish tentacles are covered with thousands of tiny stinging cells called nematocysts that fire like miniature harpoons when triggered!

The jellyfish’s transparent body helps it hide from predators in the water – they’re almost invisible in some lighting conditions!

Jellyfish don’t have gills or lungs – they absorb oxygen directly through their thin skin from the surrounding water!

Some deep-sea jellyfish have red stomachs because red appears black in deep water, helping to hide any glowing prey they’ve eaten!

The crystal jellyfish is completely transparent except for its bright glowing ring, which helps it attract prey in dark ocean waters!

The cannonball jellyfish has a firm, round bell with short oral arms and no long tentacles, making it look like a swimming mushroom!

The blue button jellyfish isn’t actually a true jellyfish but a colony of hydroids that form a disk shape with a single feeding polyp in the center!

Behavior and Intelligence

Even without a brain, jellyfish can respond to their environment and change their swimming direction when they detect changes in light or water movement!

Some jellyfish, like the Box jellyfish, have groups of eyes that can detect light, darkness, and even see images, helping them navigate around obstacles!

Jellyfish often swim toward the surface during the day and deeper at night, a behavior called vertical migration!

Some jellyfish species can detect vibrations in the water, which helps them sense when predators or prey are nearby!

The upside-down jellyfish spends most of its time resting upside-down on the ocean floor to allow algae in its tissues to receive sunlight for photosynthesis!

When threatened, some jellyfish can pull in their tentacles and increase their pulsing rate to swim away faster!

Jellyfish don’t actively seek out humans to sting – most stings happen when people accidentally touch or swim into jellyfish tentacles!

Box jellyfish can move in specific directions, navigating around obstacles and even swimming against currents!

Jellyfish in aquariums will sometimes gather on the side of the tank where there’s less water flow, showing they can respond to their environment!

Habitat and Survival

Jellyfish populations often bloom (increase rapidly) when ocean conditions provide more food and fewer predators!