What Are Jellyfish & Interesting Jellyfish Facts

The ocean is a mysterious place, and there is a certain critter that stands out above the millions of others, Jellyfish! Jellyfish come in many shapes, sizes, and colors. Some jellyfish are dangerous while others are not. But jellyfish are not as easy to understand as they may look.

What Are Jellyfish?

Jellyfish or jellies are soft-bodied free-swimming aquatic animals with a gelatinous bell shaped body and trailing tentacles on the underside of their body. They move by contracting their bodies and do not have much control over where they go. Most jellyfish drift with the water currents and are made up of more than 90% water. Jellyfish are not even actual fish. This is a bit of a misconception as they’re really just oversized zooplankton that freely float in the ocean currents.  The confusion exists because they can be qualified as a plant, animal, and also categorized with sea anemones and coral.

The Basic Anatomy of Jellyfish

Roughly 95-98% of jellyfish bodies are made up of water and the other five percent of a jellyfish’ body is made of solid matter which gives them the free floating ability and their translucent appearance. Jellyfish are simple creatures in the fact that they lack a brain, heart, bones or even blood.

Jellyfish have a simple nervous system that gives them the ability to smell, detect light and react to stimuli. Even though jellyfish can smell, they lack lungs or any form of a respiratory system like most mammals.

Jellyfish have both oral arms and tentacles. Depending on the species, the number of tentacles may vary from four to eight.  The tentacles are not merely used to control vertical movements but also to sting and capture their prey. The simple digestive cavity of a jellyfish acts as both its stomach and intestine, with one opening for both the mouth and the anus. While jellyfish can move up and down with ease, their bell shape restricts any horizontal movement which makes them poor dance partners.

Jellyfish are also perfectly symmetrical and if you were to slice one in half, the parts would mirror one another. We don’t recommend slicing any in half and testing this for yourself, just take our word for it.

The Jellyfish Life cycle

How life begins for jellyfish are another unique quality.  They have thrived and survived because they can reproduce both sexually and asexually. This fact is how they have survived and thrived for over 700 million years.

During mating season, adults release sperm and eggs into the surrounding water, where the eggs are fertilized and grow into new organisms. In some jellyfish species, eggs attach to a pouch surrounding the mouth.  The eggs then are fertilized when the egg-bearer swims through another jellyfish’s sperm. Another way fertilization may occur is through harboring the eggs inside their mouth, and then the sperm is absorbed through their stomach.

Jellyfish development occurs in multiple phases. Once sperm has fertilized the eggs they will develop into larval planulae.

When the fertilized eggs hatch, they float to the top of the water. Many are eaten by predators in the wild and the ones that survive the larvae stage begin to sink into the ocean to develop into a polyp. As the polyps mature,  it creates a colony from its body as more polyps are produced. They then bud into ephyrae and then transform into adult medusae.

In the wild, jellyfish can survive and live anywhere from a few hours to a months. Aquarium jellyfish can live anywhere from a few months to over a year if properly cared for. Pet Moon Jellyfish will live anywhere from 6 months to a year in a jellyfish aquarium.

Where Do Jellyfish Live?

There are over 1000 species of jellyfish in the world that are living nearly everywhere in the ocean. Some species survive best in Arctic waters while others live in the warmer waters near the equator. The beauty about jellyfish is their ability to adapt and thrive wherever they are.

A polyp’s habitat is whatever it latches onto before maturing into an adult jellyfish (medusa).  They form blooms that number in the thousand and the saltier the water, the larger the bloom.

Jellies often use the current and their body to travel without expending energy. But even the tamest of currents can overwhelm them because of their lack of brain, blood, and central nervous system and fast currents can cause harm.

What Do Jellyfish Eat?

Jellyfish are not picky when it comes to eating and the free-floating ocean creatures are considered opportunist predators. The size of the jellyfish plays a large role on what they decide to capture and ingest. Smaller jellyfish may only eat eggs and plankton while larger species can consume larger prey or even other jellies. When it comes to pet jellyfish, baby brine shrimp seem to be a favorite.

The process of capturing their prey is another way jellyfish are unique. By using their tentacles, they sting their prey into paralyzation or death. Often times the prey they kill are too large for them to even eat because as they float freely with only their sensory system, the size of what they are attempting to devour is unknown. Their mouth lies underneath their belly and can only fit so much. The size of their bell-shaped body is a giveaway as to how large their mouths are.

Some jellyfish also will eat their own. The choice in food makes them more than simply opportunist but also cannibalistic.

Jellyfish Fishy Facts

  1. Have you ever wondered how much water a jellyfish is made of causing their transparency?  – While humans are made of seventy percent water, most jellyfish are ninety-five percent H2O.
  2. How long have jellyfish been on earth? – Jellyfish came long before humans. The majestic, floating predator have survived for over 700 million years.
  3. There are jellyfish species that are larger than humans, while others are as small as the head of a needle.
  4. Did you know a group of jellyfish is not only known as blooms but also by “swarms” or “smacks.”
  5. Not all jellyfish sting. While, others can kill humans with their poison.
  6. Some jellyfish glow in the dark and would make great nightlights.
  7. Not all jellyfish even tentacles.
  8. Powdered jellyfish can be used in food.
  9. The goo that jellies release could be used to power medical devices.
  10. Jellyfish are so willing to eat anything that they will even eat peanut butter.