Adipose eyelid

An adipose eyelid is a transparent eyelid found in some species of fish, that covers some or all of the eye. They are most commonly found on deep sea (benthic) fish, but can also be seen on non-benthic fish. Fish with this feature include milkfish, isospondyls (including herring), jacks, mullets, and mackerel. The overall anatomy of the eyelids plays an important role in understanding their possible purpose.