Homeostasis is the state of steady internal, physical and chemical conditions maintained by living systems. This is the condition of optimal functioning for the organism and includes many variables, such as body temperature and fluid balance, being kept within certain pre-set limits. Any organism whose internal environment is highly influenced by external factors is conformer. Many marine invertebrates are conformers: they have no need to control their internal environment since the external environment is fairly constant in terms of temperature, oxygen tension and nutrients. Conformers cannot maintain their constant internal environment.