Here's why:
* Lack of a backbone: Invertebrates are animals that lack a backbone or spinal column. Leeches, like all other worms, do not have a backbone.
* Belong to the phylum Annelida: Leeches are segmented worms, belonging to the phylum Annelida. This phylum encompasses creatures like earthworms and marine worms, all of which are invertebrates.
* Other characteristics: Leeches possess other characteristics that classify them as invertebrates, such as:
* A soft, segmented body
* A closed circulatory system
* A simple nervous system
Vertebrates, on the other hand, possess a backbone and other characteristics such as:
* A skull
* A complex brain and nervous system
* A well-developed circulatory system with a heart
* A distinct internal skeleton