An arachnologist
A virologist is a scientist who studies viruses.
A scientist who studies animals is called a zoologist.
A scientist who studies radioactivity is called a nuclear physicist or a radiologist.
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.
Parasitologist
geologist
physicist
environmentalist
ecologist