Whether decking out an alien world with life in a game session, or story, it is important to know how best to suspend disbelief when dealing with non-Earth organisms.
Life can come in literally any imaginable, and unimaginable, shape, size and disposition. Whether it's how we know it or don't, life is an adaptable beast where change is what allows it to survive. Yet, life isn't entirely random and prone to inconsistencies. Because while the evolution of beasts brings about random mutation, only certain elements survive and continue.
Nature keeps many patterns, and follows them to the letter. And we shouldn't forget this when designing alien life on distant planets. It might have worked in old pulp comics from yester-decade where the male sentient was a ghastly beast of many limbs and hazardous body, while the female member was attractive, if not lacking in non-humanity.
There is consistency, design and purpose behind life and how it comes about. Let us look at our own organisms of Earth. Here we would find that vertebrate life, while often very different from each other, all possess four limbs, a head with eyes and mouth, tails or remnants, similar bone structures, genetalia positioned at the rear, and etc. So unless we're designing a very pulpy sort of alien ecosystem, we can expect to see various examples of divergence that also feature convergent form and utility, but this shouldn't discourage one from making everything too "samey". Rather, we should see worlds with a lot of invertebrate creatures, each filling their niche in life, or on the other hand, perhaps various vertebrate things where each runs on four to six legs, with some species instead using the fifth and sixth limbs for manipulation.
Whether it's spines, body structures, psionic powers, wings, or what-have-you, consistency in form and pattern makes for standardized and believable life, while divergence and biodiversity makes for realistic life. Stay creative, friends!
Alternatively, you can just give me the finger and continue on with ant-men and their sensuous babe-queen. 'Cause fun is what counts in the end, and not necessarily dedicating too many resources to one facet of an adventure your railroad-hating players might not even run into.