Bulla cf. striata
The shell of this mollusk is thin and delicate, smooth, oval and inflated with a depressed spire. The aperture is longer then the shell and is rounded at both ends, narrow posteriorly and flaring anteriorly. The lip is thin and slightly constricted centrally.
Spotted this in about 30m of water at Dayang Beach, Talikud Island. It measured 2cm long. (Not 100% sure if this is Bulla striata.)