Boekind was a species from the Silver Devastation.
Biology
Boekind were large, humanoid heads with numerous tendrils which terminated in round pod-like structures in place of hair. (TV: The End of the World)
Boekind could communicate telepathically and were able to speak, although they often preferred telepathy. (TV: New Earth, Gridlock)
Life cycle
Based on a newscast by Bad WolfTV, it was possible for a member of Boekind to become pregnant and (TV: The Long Game) their young were called Boe-lets. (PROSE: Time Traveller's Diary)
Technology
The Face of Boe at least lived permanently in a life support tank with added teleportation capabilities. (TV: The End of the World, New Earth, Gridlock)
History
In the year 200,000, which the Ninth Doctor knew to be the time of the Fourth Great and Bountiful Human Empire, the Face supposedly gave birth to the Boemina. (TV: The Long Game) It was during the Fourth Great and Bountiful Human Empire that Boekind became all but extinct, whilst the Face of Boe lived on. (PROSE: The Time Traveller's Almanac)
Indeed, by the time of his hospitalisation and near-death in 5,000,000,023, the Face was the last of his species. (TV: New Earth) He later sacrificed himself to save the inhabitants of New New York in the year 5,000,000,053, rendering Boekind extinct. (TV: Gridlock)