ursinology?
Ursinologist
Since the bear genus name is ursus, and the term ursusology is applied to the acts of studying bears, I humbly submit the word "ursusologist" for one who studies the various types of bears.
A scientist that studies bears would be called an ursinologist.
The name of a scientist that studies sports is called a sports scientist.
An arachnologist
A scientist who studies crystals is known as a Crystallographer.
A scientist who studies animals is called a zoologist.
A scientist who studies animal life is a zoologist. There is no particular name for a scientist that specialises in platypuses.
The name for this type of scientist is a teuthologist
This answer is a entomologistA scientist who only studies fish is called an ichthyologist.
environmentalist
ecologist
Astronomer
A botanist