There’s more types of Metroids than just the little blobby guy who made a cameo in Kid Icarus…
In their “natural” environment on SR388, Metroids go through at least 7 developmental stages from egg to omega.
There’s also a Queen variant but it’s unknown if an Omega Metroid will become a Queen in the right circumstances or if there are special eggs that produce new Queens. (This is how the Queen appears in Metroid 2 on the Game Boy and in the fan-developed Metroid 2 Remake.)
However, when exposed to different environments and circumstances, you can get some of the interesting variants seen in the latter Metroid games.
Check it out on MetroidGuide.com.