Cossals are a class of tetrapodal animal similar to mammals in overall structure with minor differences.
The single defining feature of cossals, and the source of the name, is an organ near the heart called the cossary organ or gland that serves to improve the organism to allow it to perform certain tasks better. Examples of this are some semi-aquatic species that may develop aqualung cossary organs to aide in underwater hunting.
Another major difference between mammals and cossals is the way they are born. In cossals, the female develops a large, rigid, internally cushioned chamber on her abdoment that has a food source and heating compounds within it that the infant develops in. This is shed within the first few months of 'pregnancy' and can develop entirely independantly from the mother until the infant(s) emerge from it. As cossals, all civilised races on AulCeles exhibit this process.
Cossals are typically bilaterally symmetrical, including internal structures and organs. This tends not to be true of their external markings though which are usually assymetrical.
All four of the sentient races of AulCeles are cossals.