A herpetologist.
A person who studies snakes is called a Herpetologist.
I think your thinking of an OB/GYN; OB/GYN: A commonly used abbreviation. OB is short for obstetrics or for an obstetrician, a physician who delivers babies. GYN is short for gynecology or for a...
A Hydrologist.
A radiologist.
virologist