The Common Rorqual Whale (Balaenoptera musculus)

Date 1903
Source http://www.flickr.com/photos/biodivlibrary/6358178351
Author Harry Hamilton Johnston
Full title British mammals; an attempt to describe and illustrate the mammalian fauna of the British islands from the commencement of the Pleistocene period down to the present day, by Sir Harry Johnston.
Source: https://commons.wikimedia.org/wiki/File:British_mammals_(6358178351).jpg

The blue whale (Balaenoptera musculus) is a marine mammal belonging to the baleen whales (Mysticeti). It is the largest animal known to have ever existed. Blue whales were abundant in nearly all the oceans on Earth but their numbers have been greatly reduced due to whaling.