Coelenterates comprise such animals as hard corals, soft corals, sea fans, jellyfish and sea anemones. Nearly all are marine and the majority are sessile, that is they are permanently fixed to the substrate, and most of these do not move around as adults.

Their body mass is composed of three layers: an outer layer of cells called the ectoderm; an inner layer of cells called the gastroderm (also entoderm or endoderm); and a gelatinous/fibrous mesogloea layer containing cells that is sandwiched in between.

In jellyfish, most of the animal is made up of this mesogloea. Many coelenterates also have a supportive skeleton made from chitinous or collagenous material, and/or calcium carbonate.

Another major characteristic of coelenterates is they possess stinging cells called nematocysts, which are mainly located on tentacles or tentacle-like structures, and are used for defence and capturing live food.

The MAGNT coelenterate collection includes over 9000 octocorals, mostly sourced from Australian waters and shallow, tropical and subtropical regions of the central-west Pacific across the Indian Ocean to the Red Sea. There is also comparative material from such regions as Antarctica, New Zealand, and the Caribbean.

The MAGNT assists with external research projects on box jellyfish, and handles enquiries on venomous marine animals.

This section is also responsible for the curation of the Ascidian collection. Although the collection is available for external study, no research is currently conducted by MAGNT staff.