Some of the unusual biomes for fictional alien lifeforms are:

* Sun's Corona. It is speculated that at some point charged plasma particles may exhibit cell-like and dna-like behavior, potentially giving birth to plasma-based lifeform. Such lifeform was featured in a short story "Out From the Sun" by Arthur C. Clarke, published in 1958.
* High pressure environment, such as "surface" or depths of Jupiter. In this environments common gases would turn into metals. Those were featured in "Call me Joe" story by Paul Andersson, written in 1957. 
* Surface of neutron star. This sort of unusual biome was featured in "Dragon's Egg" by Robert L. Forward, written in 1980. 
* Methane world, where Methane is used instead of water. An example of creature from such world was featured in "Snow maiden" short story, written by Kyr Bulychev, in 1973, featuring an alien woman with body temperature below -70 degrees celsius.
* Charged dust clouds. It is speculated that charged dust clouds scattered in space may, in some situation, develop life-like properties, using electric charges.

Note that those sorts of biomes would be largely incompatible with earth-based carbon lifeforms, and would not be suitable for biomes on a single planet.

For planetary biomes, following biomes and evolutionary alterations are possible:

* Low density atmosphere area. It will create lifeforms with increased lung size, and large surface area, assuming the lungs would evolve. 
* Alternative symmetry. Majority of mammals use bilateral symmetry. A biome where radial symmetry is used will result in a vastly different appearance of lifeforms, for example mimicking that of a starfish. Five legged creatures would be possible.
* Different number of limbs. Most mammals possess 4 limbs. In a situation where evolution develop different number of limbs, worlds with centaurs or winged creatures become possible.
* Increased amount of oxygen. Increased presence of oxygen allows larger insects. At the same time, it produces a much more dangerous fires.
* Sunless or distant world. The sun barely gives any energy, and the planet is covered with crystallized gases and rivers of helium, without an atmosphere. Existing creatures would possess heavy insulation, hunt for heat sources.
* Geothermal world. Frozen water world without sun, where life developed in oceans covered with eternal life,' with their only source of power being geothermal power of the planet. May produce civilization of blind creatures, or civilization without astronomy.
* High gravity world. This sort of environment could produce flattened creatures, flight would be unthinkable, and fall would be fatal.
* Low gravity world. This can produce large, fragile creatures capable of floating.

Many other possibilities are possible.
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