Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. Cow sharks, or the Hexanchidae, are a family of sharks characterized by an additional pair or pairs of gill slits. There are currently known to be four species in three genera, Heptranchias, Hexanchus and Notorynchus. Cow sharks are considered the most primitive of all the sharks, because their skeletons resemble those of ancient extinct forms, with few modern adaptations.

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