# Life cycle that may have influenced that of the Xenomorph #

It has recently been suggested that ***Phronima*** was the inspiration behind the Xenomorph:

 - [Meet Phronima, the Barrel-Riding Parasite That Inspired the Movie *Alien*][1]
 - [Deep-Sea Creatures That Inspired the *Alien* Series][2]

![enter image description here][3]

From the [Wikipedia article][4] concerning Phronima:

> Although commonly known as parasites, they are more technically correctly called *parasitoids*. Instead of constantly feeding on a live host, females attack salps, using their mouths and claws to eat the animal and hollow out its gelatinous shell. Phronima females then enter the barrel and lay their eggs inside, and then propels the barrel through the water as the larvae develop...

*If*  the articles above are correct and Phronima is indeed the inspiration behind the Xenomorph, then it is easy to see how one might extrapolate the Xenomorph's life cycle from Phronima's.

# Life cycle that is *more* like that of the Xenomorph #

However, Phronima's life cycle is not *exactly* that of the Xenomorph.  For an animal using **intermediate offspring** to reproduce, I would nominate ***[Cnidaria][5]***, which **@Hypnosifl** has already mentioned prior to my answer.  Cnidaria includes jellyfish and the common sea nettle.  A group of the latter is pictured below:

![enter image description here][6]

Here is a pictorial representation of their life cycle:

![enter image description here][7]

Steps 4-8 show the growth and release of the "polyp", an intermedia offspring which will give rise to the "medusa", which is the full animal.

In regards to plant species, ***ferns*** are a good example of a plant that uses an intermediate offspring to reproduce.

# Another interesting *Alien*-esque life cycle in nature #

May I present to you ***[Dicrocoelium Dentriticum][8]***, better known as the ***Lancet Liver Fluke***, a.k.a. ***["Captain Higgins"][9]*** :

 - Its eggs are defecated by a cow or horse, etc.
 - The eggs are eaten by snails, where they hatch into larvae
 - The larvae mature to juvenile stage within the snail
 - As a reaction, the snail grows a cyst to surround the juveniles, and then the parasite-filled cyst is ejected by the snail
 - The juvenile flukes are in an egg again, but they used the snail to create it for them
 - The cyst-egg is consumed by an ant, where it breaks open
 - The juveniles flow and/or burrow up to the ant's brain and latch onto it causing the ant to climb a blade of grass each evening until the blade of grass (and the ant and the juvenile flukes) are consumed by a cow or horse
 - Inside the cow or horse, they mature into adults and lay eggs
 - Poo, repeat

![enter image description here][10]

Again, not quite the life cycle of the Xenomorph, but there is a two-stage process here that involves at least three animals being seeded along the way.

# Upshot #

Various life cycles in nature — e.g. Phronima, Cnidaria, Ferns, Lancet Liver Flukes — have features in common with that of the Xenomorph.  However, the facehugger, which is a wholly separate lifeform that lays its own egg via a proboscis into a host, seems to be unique to the Xenomorph.  I can find no evidence for it in the "real world".

In a sense, the thing that comes closest is *common bisexual animal reproduction*.  The only caveat is that sperm don't lay their own eggs!


  [1]: http://www.iflscience.com/plants-and-animals/meet-phronima-barrel-riding-parasite-inspired-movie-alien-0
  [2]: http://deepseacreatures.org/interesting/deep-sea-creature-that-inspired-the-alien-series
  [3]: https://i.sstatic.net/VlyAd.jpg
  [4]: http://en.m.wikipedia.org/wiki/Phronima
  [5]: http://en.m.wikipedia.org/wiki/Cnidaria
  [6]: https://i.sstatic.net/Z9bcn.jpg
  [7]: https://i.sstatic.net/Yk3Fw.jpg
  [8]: https://en.wikipedia.org/wiki/Dicrocoelium_dendriticum
  [9]: http://theoatmeal.com/comics/captain_higgins
  [10]: https://i.sstatic.net/6Ue6U.png