Scyphozoa

The Scyphozoa are a group of animals that live only in the ocean and belong to the phylum Cnidaria. They are known as the true jellyfish or "true jellies." These creatures have been around since the earliest times, from the 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. True jellyfish are fascinating because they are very old animals that have lived in our oceans for millions of years.

Biology

Most Scyphozoa, known as true jellyfish, have two main stages in their life cycle. One stage is called the medusa, which floats in the water and is often seen in warm summer months. The other stage is a polyp that lives on the ocean floor and produces new medusae each season. Many of the large, colorful jellyfish you might see in coastal waters are Scyphozoa. They usually range from 2 to 40 cm in diameter, but the largest species, Cyanea capillata, can be up to 2 meters across.

These jellyfish live in oceans all over the world, from the surface to deep waters, but they never live in freshwater or on land. As medusae, they eat small animals like crustaceans and fish using special stinging cells called nematocysts on their tentacles and oral arms. Some species also filter-feed on plankton by straining it from the water with their tentacles.

Anatomy

Scyphozoans, also known as true jellyfish, have a special gel-like material called mesoglea inside their bodies that helps them stay structured without a skeleton. Unlike some other jellyfish, they swim by using muscles around their edges to push themselves through the water.

These jellyfish don’t have heads, skeletons, or special organs for breathing and waste removal. Their bodies are mostly water—up to 98% in some species—which makes them hard to find as fossils. Inside, they have a stomach connected to four main channels, and some even have extra tiny mouths on their arms. Their nervous system is spread out, helping them move and sense their surroundings.

Commercial importance

Some types of Scyphozoa, like the moon jelly Aurelia aurita and the enormous Nemopilema nomurai, are important because they are caught for food. The jellyfish that are fished for food belong to a group called Scyphomedusae in the order Rhizostomeae. Most of these jellyfish live in warm water and can sometimes cause problems for fisheries.

Taxonomy

The Scyphozoa, also known as true jellyfish, are a class of marine animals. They were once thought to include other groups like Cubozoa and Staurozoa, but now they are known to have three main orders. Currently, about 200 species of Scyphozoa are known, with likely many more waiting to be discovered.

The Scyphozoa class includes several subgroups:

• Subclass Coronamedusae

  • Order Coronatae
  • Family Atollidae
  • Family Atorellidae
  • Family Linuchidae
  • Family Nausithoidae
  • Family Paraphyllinidae
  • Family Periphyllidae

• Subclass Discomedusae

  • Order Rhizostomeae
    • Suborder Daktyliophorae
      • Family Catostylidae
      • Family Lobonematidae
      • Family Lychnorhizidae
      • Family Rhizostomatidae
      • Family Stomolophidae
    • Suborder Kolpophorae
      • Family Cassiopeidae
      • Family Cepheidae
      • Family Mastigiidae
      • Family Thysanostomatidae
      • Family Versurigidae
  • Order Semaeostomeae
    • Family Cyaneidae
    • Family Drymonematidae
    • Family Pelagiidae
    • Family Phacellophoridae
    • Family Ulmaridae

• Order †Byroniida (possible stem coronatids)