The most commonly referred to Jellyfish belongs to the class of Scyphozoan. They are disc shaped animals that are seen floating near, or beached, the shore. Jellyfish are one of the most beautiful and awe inspiring creatures of the ocean, certainly one of the most popular attractions at public aquariums.

Within the class of Scyphozoan are the orders of Semaeostomeae, which contains 50 described species of mainly coastal water jellyfish, including the popular Aurelia and Chrysaora. The order Coronatae include 30 described species of deep sea jellyfish. The order Rhizostomeae contains 80 described species, which include the Cassiopea jellyfish, seen often in petshops, who swim upside down as they contain, and expose, their photosynthetic symbiotic algae to sunlight. The order Stauromedusae consists of 30 described species, which are the non swimming stalked jellies that are generally found in cooler waters. They are vase shaped and fixed by a basal stalk. Their mouth is pointed upwards

Jellyfish, or Sea Jellies, are made up of 99% water, and are found all over the world and in all the seas, even in some freshwater locations. A jellyfish's body is made up of two layers, and in between is a  jellylike substance, which is how they get their name. Their bodies range in size from 1 to 16 inches, with a few species attaining  up to 6 feet across and 15 feet in length. 

Most Jellyfish have very short lifespans and may live for only a few weeks, or at the most a
couple of years and feed on small plankton type animals that they capture within their tentacles, which have stinging cells, called nematocysts. 

The life cycle of Scyphozoan jellyfish consists of three stages ; Adult jellyfish sexually produce eggs and sperm and the larvae is,  either 'brooded' within the gut of the adult or develops as a free swimming planula. The planula settles onto a substrate, the hydratuba stage, and develops into an adult, or scyphistoma. The scyphistoma, which is a sessile or stationary polyp, asexually buds off a small medusa, called an Ephyra, which develops into an adult. 

Midwater Systems has developed a custom acrylic jellyfish tank, called the Jelliquarium, and is working on holding systems used to keep these midwater collections and gelatinous organisms in suspension.

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