Here's why:

* Vertebrates are animals with a backbone (spinal column).

* Invertebrates are animals without a backbone.

Fungi are a separate kingdom of life entirely, distinct from the animal kingdom. They have their own unique characteristics, including:

* Heterotrophic: They get their food by absorbing nutrients from their environment.

* Multicellular (except for yeasts): They are made up of many cells.

* Chitin cell walls: Their cell walls are made of chitin, a tough, fibrous substance.

* Spore reproduction: They reproduce using spores.

So, while fungi are often found in the same environments as animals, they are not classified as either vertebrates or invertebrates.