pearl oyster
Especially refers to Marten's pearl oyster (Pinctada fucata martensii), also known as 阿古屋貝 (あこやがい).
See also: アコヤ貝
A beautiful pearl was harvested from the pearl oyster.
Compound of 真珠 (しんじゅ, 'pearl') and 貝 (かい, 'shellfish'). The reading がい is a rendaku form of かい.