Why protonephridia are termed as flame cells?

i believe it is "they are not used up by reactions" as the answer to your question, text me back if this is correct because i just learned this.

the relative standard reduction potential of the half-cell in which reduction occurs; more positive than the other half-cell. reduction is a chemical process in which electrons are added to an atom or an ion; it always occurs accompanied by oxidation of the reducing agent.