Are invertebrates and vertebrates universal?

Question

Im making a speculative biology project and I was wondering if vertebrates and invertebrates are universal classes of animals that if animals were to evolve on other planets, would they be able to be classified as invertebrates or vertebrates ?

Answer 1

NO

Life on earth is over 4.5 billion years old. Vertebrates evolved about 500 million years ago.

That is, the classification didn't even apply on this planet for more than 80% of life's existence on it. It is improbable that we could be confident that the same anatomy would appear elsewhere.

Answer 2

I'm not sure this is Worldbuilding, but...

Simplistically, Yes

Vertebrates have spines, invertebrates do not. Convergent evolution would suggest that if there's a biosphere where life evolves that's anything like Earth, you'd get earth-like animals eventually.

The reason spines are so common is because they're useful, structurally speaking. Not only can you hang other bits (like ribs and whatnot) off of them, but having a protected column to store your high-bandwidth nerves in is beneficial from a survival perspective.

Now, if it's not an earth-like planet (all water, say, or a Venutian-style atmosphere with something like floating plankton), then all bets are off over whether something spinelike will evolve at all, but in that case, the classification is trivial - they're invertebrates.

(All this assumes that humans are the ones doing the classification. If the dominant sapient form of life on this speculative planet are cephalopods, they may not place much importance in spines, and would use a different classification system.)

Answer 3

No more than winged and no wings, or legged and no legged, shelled or unshelled. But we don't use these as biological classifications on Earth simply because they have occurred multiple times independently of a common ancestors, as well as disappearing and re-appearing or being the result of convergent evolution. Therefore these classifications are not useful for delineating evolutionary branches.

If we suddenly found evidence of a branch with vertebrae disappearing and re-appearing, or appearing independently of inheritance from a common ancestor of other vertebrates, then the classification of vertebrates vs invertebrates becomes similar to those I described at the beginning and is therefore no longer useful for delineating evolutionary branches or common ancestors.

The thing about classifications, is that classifications are rather arbitrary human constructs and you can classify things however you want. Ultimately you have to ask yourself: is the classification useful for your purpose? On a world where spines have evolved multiple times independently but all winged animals have wings because they all inherited them from a common ancestor then suddenly wing vs wingless becomes a very useful classification while vertebrates vs invertebrates becomes a useless for taxonomy.

Example 1: If you found two planets where vertebrates and invertebrates evolved and inherited that trait from a common ancestor unique to each planet (i.e. useful for taxonomical classification), you still would not group these vertebrates (or invertebrates) from both planets under the same group if your goal is taxonomy. It doesn't make sense. It's not useful for taxonomy since they are just results of convergent evolution.

Example 2: What if an animal had a central nerve bundle protected by a rigid column that ran through it's body laterally (rather than longitudinally). Does that count as a spine? Is that a vertebrate? Would it be useful to group that animal in with other vertebrates having dorsal spines for taxonomical purposes even though its completely unrelated?

(It's really freakin' unlikely that the spin would rotate 90 degrees such that dorsal and lateral "spined" animals share a common ancestor.)

Example 3: What if the world only ever evolved invertebrates? Spines never evolved? Would it be useful to classify everything on that world as invertebrate? If we did that on Earth it would be like dreaming up a taxonomical classification for something we have never seen (left-handed helix DNA for example) and then putting every organism under our sun in the opposite classification.

So in short if I were to answer your question literally, as worded, the answer would be yes. But if I am correctly understanding the intent of your question, the answer would be no.