Do all fish have gills covered by operculum?

Characteristics of operculum:

1. All fish having gills are not covered by operculum.
2. Operculum is present in bony fish, hence forms gill covering for bony fish.
3. Operculum is series of bones.
4. It provides facial structure to bony fish.
5. It is a protective covering for gills in bony fish.
6. Thus, gills are covered by operculum in only bony fish.