Dysidea etheria have a simple immune system which distinguishes itself from that of other organisms, that have very complex immune systems. The immune system of a sponge will not accept body tissue from another species, immediately recognizing it as a pathogen, when it could actually prove useful to the sponge. On the other hand, if another Dysidea etheria donates the same type of tissue to the organism, the immune system of the sponge will accept it. If the immune system of the sponge finds a pathogen something known as gray cells will attack it and destroy it. They will first send off chemicals that stop it from spreading any further. If that doesn't work they will release a chemical that destroys the pathogen.