Adipose eyelid
An adipose eyelid is a transparent eyelid found in 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. Some fish that this feature is found on include: milkfish, herring-like isospondyls, jacks, mullets, and mackerel. The overall anatomy of the eyelids plays an important role in understanding their possible purpose.