cytologist noun
a biologist who studies the structure and function of cells
cy·tol·o·gy -noun the study of the microscopic appearance of cells, esp. for the diagnosis of abnormalities and malignancies.
Extract from "San Diego Zoo" page in Wikipedia - Many species are breed in captivity for release into their native habitats where appropriate. It employs numerous professional geneticists, cytologists and veterinarians and maintains a cryopreservation facility for rare sperm and eggs called the Frozen Zoo.
Cyto- means "cell". So a cytobiologist studies cells. Another name is cytologist.