Platyhelminthes have [[1]]  for the excretion.

Concept:  In Platyhelminthes, there is the flame cell which helps in the excretion of the waste materials.
In Platyhelminthes, there is only one opening, which is the mouth through which egestion and ingestion.
So in Platyhelminthes, the anus is not present but that does not mean that the Platyhelminthes excretory system is absent.
Platyhelminthes have flame cells for excretion.
Hence, flame cells are the correct answer.