The context for this is that a PC druid that is not yet level 8, wants to achieve flight by using the Wild Companion feature from Tasha's Cauldron of Everything to summon a familiar with a fly speed like an owl, and then turn themselves into a small creature like a crab with their Wild Shape that the owl will then carry, thus achieving flight.
So the question is can they have Wild Companion and Wild Shape active simultaneously?
The Wild Companion feature you gain at 2nd level says:
You gain the ability to summon a spirit that assumes an animal form: as an action, you can expend a use of your Wild Shape feature to cast the find familiar spell, without material components
The Wild Shape feature (also gained at second level) says:
Starting at 2nd level, you can use your action to magically assume the shape of a beast that you have seen before. You can use this feature twice. You regain expended uses when you finish a short or long rest.
So you have two uses of Wild Shape per short rest. You could spend one of them to summon a familiar and the other one to transform with Wild Shape. There is nothing that states that you cannot use both uses at the same time; only, normally if you use the Wild Shape to transform a second time, you of course lose your original transformation.
The kinds of beasts you can transform into is only limited by CR, and that they originally may not have a fly speed. A crab would qualify.
