No, leeches are definitely not single-celled organisms. They are multicellular animals, belonging to the phylum Annelida, which also includes earthworms and other segmented worms.

Here's why:

* Complexity: Leeches have complex body systems like digestive, circulatory, and nervous systems, which require multiple cell types and tissues to function.

* Size: Leeches are macroscopic, meaning they are visible to the naked eye. Single-celled organisms are microscopic.

* Structure: Leeches have a segmented body, distinct head and tail regions, and specialized structures like suckers for attachment. This level of organization is impossible in a single-celled organism.

So, while leeches might be small and slimy, they are far from simple! They are actually quite complex creatures with a fascinating anatomy and physiology.