All mysticetes, are slip into 4 families.They are large whales with baleen instead of  sharp teeth.

Baleen is a long plates inside the mouth made of keratin which filters their prey.

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Keratin is a  substance also found in human's fingernails and hair.

This mean the baleen is used differently among species (gulp-feeding with balaenopterids, skim-feeding with balaenids, and bottom-feeding with eschrichtiids).

 

All of these whales have double blowhole, a symmetrical skull and one sternum bone.

They can be found in all oceans and can take the longest migrations known to man.