malacology
The scientific study of mollusks, a branch of zoology.
He is majoring in malacology at university.
貝類学 is a synonym for malacology, but 軟体動物学 is more precise as it refers to the phylum Mollusca, while 貝類学 can sometimes be used more broadly for shell-bearing animals.
Compound of 軟体動物 (なんたいどうぶつ, 'mollusk') and 学 (がく, 'study'). The term is a direct calque of the Western scientific term 'malacology'.