Scyphozoa

The Scyphozoa are a group of animals that live only in the sea, and they belong to the phylum Cnidaria. These animals are known as the true jellyfish or "true jellies." They are very interesting because they have been around for a very long time, from the earliest Cambrian period until today.

The name Scyphozoa comes from an ancient Greek word, skyphos, which means a kind of drinking cup. This name was chosen because the shape of these jellyfish often looks like a cup. These creatures are very important for scientists who study life in the ocean because they help us understand how animals have changed and stayed the same over millions of years.

Biology

Most true jellyfish, called Scyphozoa, live in the ocean. They have two main stages in their life. One stage is called a medusa. It floats in the water, especially in warm summer months. The other stage is a polyp. This is a smaller form that lives on the ocean floor and makes new medusae.

These jellyfish can be small, from about 2 to 40 cm (1 to over 15 inches) across. But some species, like Cyanea capillata, can grow as large as 2 meters (about 6 feet 7 inches) wide. They eat small sea animals such as crustaceans and fish. They use special stinging cells called nematocysts on their tentacles to catch food. Some jellyfish also eat by filtering tiny plants and animals called plankton from the water with their tentacles. All Scyphozoa live in the ocean. They are never found in freshwater or on land.

Anatomy

Scyphozoans, or true jellyfish, have a special gel-like material inside called mesoglea that helps them stay upright. Unlike animals with bones, jellyfish have no hard parts and are mostly water. This makes them hard to find as fossils.

These jellyfish move by using muscles around their edges. They swim by squeezing and relaxing these muscles. Their bodies have a mouth that leads to a stomach with special canals to help them eat. Some even have tiny mouths on their arms! They also have tiny cells that help them sense their surroundings and move.

Commercial importance

Scyphozoa include the moon jelly Aurelia aurita and the enormous Nemopilema nomurai, found between Japan and China. In some years, this large jellyfish can disrupt fisheries.

Jellyfish fished for food belong to the group called Scyphomedusae, and most of them live in warm water. They are part of the order Rhizostomeae.

Taxonomy

The Scyphozoa, also called true jellyfish, have an interesting family tree. Today, they have three main groups with about 200 known species. Scientists think there may be even more.

These groups include the Coronamedusae and Discomedusae subclasses. The Discomedusae subclass has two orders: Rhizostomeae and Semaeostomeae. Each order has several families, like Cyaneidae and Rhizostomatidae. These are just a few of the many true jellyfish in our oceans.