The excretory organs in a planarian or fluke are called protonephridia.

Here's why:

* Protonephridia are simple excretory organs found in many invertebrates, including flatworms like planarians and flukes.

* They consist of a network of branching tubules that collect waste products from the body fluids.

* These tubules end in flame cells, which are specialized cells with cilia that beat and create a current to draw waste into the tubules.

* The waste is then transported through the tubules and excreted from the body through pores called nephridiopores.

Let me know if you have any other questions about planarians, flukes, or excretory systems!