Science & Technology

The amazing jellies have 1,200 to 1,800 species.

Imagine living creatures that survive without a brain, heart, or lungs, are often see-through, and are are about 98% water. Well, the creatures exist and go by the names jellyfish, jellies, medusa, and sea jelly, among others. There are up to 1,800 species of the venomous ocean dwellers with varying appearances, habits, and behaviors. Jellyfish are found in aquatic environments all over the world.

• Kingdom – Animalia
• Phylum – Cnidaria
• Subphylum – Medusozoa

The animal named “jellyfish” represents more than one taxonomic group, so the scientific classification varies. The four groups of common jellyfish are Cubozoa (box jellyfish), Scyphozoa (true jellyfish), Staurozoa (stalked jellyfish), and Hydrozoa (small jellyfish).

The Oldest Multi-Organ Animal Group

Jellyfish do not have bones, so there is no fossil evidence to support the amount of time they have existed on Earth. However, scientists believe the animals have existed for 500-700 million years, which makes them the oldest multi-organ animal group. The free-swimming marine creatures have bell-shaped bodies and long tentacles and come in a variety of colors, including translucent (see-through). The bell is a hollow structure filled with a jelly-like substance called mesoglea, which is 95% water. Tentacles form at the margin of the bell and hang from the body at varying lengths. Some jellyfish use their bodies and tentacles to swim at a slow pace, while others simply drift with the current of the water.

Bells range from about one millimeter to 6.5 feet in height and diameter. The lion’s mane jellyfish, however, blows the others out of the water (no pun intended) as far as size. The tentacles of this jelly can reach lengths of 120 feet.

Jellyfish are carnivores. They use their tentacles, armed with nematocysts (stinging cells), to capture prey and defend against threats. The cells inject venom into prey, which can be rather painful. The severity of the sting varies throughout the species, but some can be fatal, even to humans. Because they are so hard to see in the water, it is not uncommon for beachgoers to experience a jellyfish sting. Some stings are superficial, causing discomfort only at the sting site. Others can lead to systemic problems, which are painful issues throughout the entire body. On rare occasions, jellyfish stings can lead to death.

What Do Jellyfish Eat?

Jellyfish indulge in plankton (their favorite), small fish, crustaceans, and even other jellyfish. They are opportunistic predators, which means they wait for the food to come to them. Because many jellies simply float, they are not able to do much hunting. Instead, they wait patiently for the food to show up where they are. Once they have stung and immobilized their prey, they bring it to their mouths located beneath their bell. Interestingly, jellies ingest food and remove waste (poop) from the same opening.

Their diets regulate populations in the marine environment and help to maintain the balance of the food chain. Like all animals, the role they play in their ecosystem is important.

From Birth to Death

Oddly enough, jellyfish are not “born.” Instead, they are “grown” as they develop as part of a complex life cycle of aquatic animals called cnidarians. They begin their lives as adult medusae (the plural for medusa) and are the familiar free-swimming jellies we have seen and heard about. Their lives are a fascinating process of sexual and asexual reproduction governed by temperature and lighting in the water’s depths.

Most jellyfish live for a span of a few hours to five years. Many factors, including the availability of food, pollution levels, water temperature, and diseases, all contribute to the life or death of the sea creature. However, one, the Turritopsis dohrnii jellyfish, is considered immortal. This jelly can regenerate itself when faced with unhealthy conditions. Any damage that comes to this animal is basically reversible, allowing them to live for millions and millions of years. Nevertheless, it is still vulnerable to predators and diseases that can lead to death.

Jellyfish are some of the most unusual and interesting animals in the ocean. Even though they do not have brains, hearts, bones, or lungs, they have survived for hundreds of millions of years by using their bodies, stinging tentacles, and drifting movements to catch food and protect themselves. These gelatinous sea creatures may look delicate, but they are powerful survivors that continue to play an important role in ocean life.

1. Jellyfish do not have bones, hearts, lungs, or brains.
2. Jellyfish are the medusa stage of the life cycle of a cnidarian.
3. A sting from a jelly can be painful and sometimes (though rarely) leads to death.