Catostylidae

Catostylidae, the fat-arm jellies, is a family of jellyfish. Members of this family are characterized by their thick, sausage-like oral arms. Members of the family Catostylidae are small marine jellyfish with domed bells. The eight short oral arms are broad and three-sided. These jellies do sting but usually only leave minor burns.

== Biology == left|thumb|Catostylus mosaicus|Catostylus mosaicus (Blue Blubber Jelly) These jellyfish have 3 layers that make up their bodies. They have an inner gastrodermis that comprises the digestive cavity. The gastrodermis possesses a single opening that functions as a mouth and an anus. The middle layer is called the mesoglea; a jelly-like substance that is flexible and dense. The outermost layer is the epidermis; it contains the nerve net. There is a network of branching canals linked with the primary ring canal, but these are not joined to the gastrovascular cavity except through the sixteen or thirty two radial canals. Some of these radial canals do not extend to the edge of the bell. There are eight sense organs, known as rhopalia, which have canals extending to the margin of the bell. Numerous jellyfish in this family rely on zooplankton as a primary source of substance. thumb|Ephyra stage of development These jellyfish swim in jerks by contracting their circular and radial muscles, which decreases the volume of water enclosed under the bell, before relaxing them again and repeating the sequence. They have no control over the direction of locomotion and drift with the currents and tides. They come in many different colors the most common are brown, clear, and blue. They are found around Africa, Australia, Spain, and South Asia. A few have also been spotted near the equator in the Americas.Sunfish, tuna, spiny dogfish, and sea turtles feed on many jellyfish of the Catostylidae family.