Reading through this thread made me think up an alien.
So, It's kind of like a nautilus where the shell has 4 insect like legs. The shell and the nautilus type thing are two separate animals but born together with connected brains so that they share a nervous system, the 2 beings work as one. The actual nautilus fleshy bit has 6 large tentacles which are used to manipulate objects. They are also land based and are about the size of a large dog.
This pretty much confirms that anyone with some imagination can think of one.
wouldent sharing one brain and one nervous system make it technically one creature? Rather then two in some kind of simbiotic state