HHGTTG

"The Haggunenons of Vicissitus Three have the most impatient chromosomes of any life-forms in the galaxy. Whereas most races are content to evolve slowly and carefully over thousands of generations - discarding a prehensile toe here, nervously hazarding another nostril there, the Haggunenons would do for Charles Darwin what a squadron of Arcturan Stunt-Apples would have done for Sir Isaac Newton.
"Their genetic structure, based on the quadruple-striated octo-helix, is so chronically unstable, that far from passing their basic shape onto their children, they will quite frequently evolve several times over lunch. But they do this with such reckless abandon that if, sitting at the table, they are unable to reach a coffee spoon, they are liable without a moment's consideration to mutate into something with far longer arms - but which is probably quite incapable of drinking the coffee.
This, not unnaturally, produces a terrible sense of personal insecurity and a jealous resentment of all stable life-forms, or “filthy rotten stinking samelings” as they call them. They justify this by claiming that as they have personally experienced what it is like to be virtually everybody else they can think of, they are in a very good position to appreciate all their worst points. This appreciation is usually military in nature and is carried out with unmitigated savagery from the gunrooms of their horribly beweaponed, chameleoid death flotilla.

Experience has shown that the most effective way of dealing with any Haggunenon you may meet is to run away… terribly fast."

Upon leaving the Milliways, Arthur, Ford, Zaphod and Marvin stole a black starship from the parking hangar. When Arthur pointed out that a fleet of black battlecruisers had been tailing their stolen ship for quite a while, and Marvin told everyone on board that they had stolen an Admiral's flagship. He knew this because he parked it, during his very long stint as a car park attendant for Milliways.

They discovered that the flagship belonged to a Haggunenon Admiral after both Zaphod and Trillian encountered the Admiral's second in command, the Underfleet Commander, each seeing them in a different form, through the visiscreen. The Second in Command's first form was of a big leopard wearing an in-flight casual spacesuit (split to the navel), then as a shoebox full of size nine Chukka boots. Both times the Underfleet Commander mistakenly assumed that Zaphod and (in turn) Trillian were the same person, due to Haggunenon's constantly changing appearances.

The Haggunenon Admiral was assumed to be still inside Milliways enjoying its meal, but it was revealed that the Admiral had been sleeping on the flagship in the form of a chair; one which Zaphod said could have been made for him due to its two headrests, which turned out to be the Admiral's eyebrows instead. The Admiral then evolved into a copy of the Ravenous Bugblatter Beast of Traal, from which Ford and Arthur were able to escape via an escape pod, but which ate Marvin, Trillian, and Zaphod. Those three later made their escape when the Admiral evolved into an escape capsule.