What is a animal smaller then thumbnail?

You're asking for something incredibly small! It's tough to find an animal that's *smaller* than a thumbnail, as most animals have some visible size. However, here are some microscopic creatures that fit the bill:

* Tardigrades (Water Bears): These amazing creatures are incredibly resilient and can be found in extreme environments. They are typically about 0.5 millimeters long, which is smaller than a thumbnail.

* Rotifers: These microscopic animals are common in freshwater habitats. They are usually around 0.1 millimeters long, making them even smaller than tardigrades.

* Amoebas: These single-celled organisms are found in various environments and move using pseudopods. They can be incredibly small, with some species measuring only a few micrometers in diameter.

* Bacteria: While not technically animals, bacteria are incredibly tiny, ranging in size from a few micrometers to a few tens of micrometers.

* Viruses: Viruses are even smaller than bacteria, with some being only a few nanometers in diameter. They require a host cell to reproduce and are not considered living organisms.

Remember, these are just a few examples, and there are many other microscopic creatures out there! The world of the very small is full of fascinating and incredible life forms.