This question was closed and since then has had no sign of interaction. I've edited it to solve all the solvable problems given in the comments, so what else must I do to get it reopened?
After a lengthy attempt to understand the scope of the query & help the OP improve it, I can at last conclude that the only thing really wrong with the question is that its OP is unwilling to edit it for improved clarity.
The answer to OP's subquestion, "what else must I do...?", is now as it's always been. Address the points of criticism (if any remain) and edit the question for focus & clarity. I'd love to answer it! And I'm sure others would as well. But it needs some fixing up, and I leave that now to the OP!
My opinion: I think there are a few pieces of information that are lacking in your original query.
I see you're working on editing your question -- that's good!
I don't see how I can answer your questions about the scales and skeleton with much specificity. How hard is wood? How sharp are thorns? To use your example: How tough is an exoskeleton. These questions can't be meaningfully answered because there are too many forms of each of these traits.
Well, I gave you two good examples of chitinous exoskeletons, one that any human can easily munch and one that might bust your teeth or rip your gums to shreds. So you can see that chitinous exoskeletons come in a wide variety of difficulty to bite through. We'd need to know roughly where your plant is on that continuum. I suggested in my comment to your Main query that you focus on one kind of tree and one kind of likely herbivore.
It's your job to give me enough background information and appropriate parameters so that I can do my job and give you a creature that has evolved to eat the tree in question. I've got ideas, but can't give them shape without you focusing on sufficient details!
To address your Meta question: you only edited the query an hour ago (as of this writing), so I don't really think you can expect it to be reopened with thousands of views, hundreds of answers and a spot at the top of the hot network questions all in that time frame!
You do have a couple of VTR, though, so clearly folks have noticed your edit and find the query acceptable.
In reading your question over, there are two aspects I'd like to ask for clarification: how thick and chewy are the stiffened cartilagenous endoskeletons?; and how thick and unbreakable are the chitinous scales? How big are the plants in question and how big are the herbivores?
Food for thought: you can pretty easily chomp an ant and eat it without difficulty; but I bet you couldn't easily crack through a crab shell without feeling some side effects.
The plants are organisms with soft cells that don't have walls.
Not clear what it refers to, your imaginary plants or real-world plants. Is it you do not know something or I do not know something?
What do they have instead? And most importantly which plants, yours? Is it a premise already or what?
Their flesh is soft,
U mean that plant matter?
Most terrestrial plants have a coat of hard chitinous scales that do not overlap,
Is it a premise? Is it what it is instead of cellulose for your imaginary plants?
There are no soft-bodied plants on land, as the soft flesh can't stand on its own. The scales often have sharp hairs or other such defences between the scales when herbivores are common
Okay, crab-like plants is probably a bold signal we are deep into a premise for a q, and in ops magic world, okay, okay, get it
as the soft flesh can't stand on its own
It is a premise or a not-so-great statement? If statement, are we in the real world again, what's going on ...
Aquatic plants generally lack the endoskeleton and have sturdier, less flexible flesh to make up for it.
Mm yeah, crab trees looking at those cellulose underwater tree weaklings with a shame
The rest is more or less okayish, formatting would be helpful.
Okay, I may see the question now, it like - here are cool plants, what cool stuff there you can suggest for animals. The legit problem, opinion-based, maybe we need to have fantasy tag or creative thinking for all that. As indeed it is hard to provide proper details and sure there are not that many options to avoid opinion-based answers otherwise.
It is still for those who answer to create required details for your setting so their answers could make sense - so you ask for creating stuff for you. Okay, maybe someone is willing, at least it seems it is now more clear what's going on.
It still needs details, it just you can't provide them, which is understandable. Yeah, we definitely need some tag for such cases.
For questions regarding the viability of a life-form design. These questions should focus on biologically plausible creatures
- no, definitely not it
Use this tag to mark questions related to creating plausible alien biologies that may be close to or far removed from Earthly biology but within the realms of hard science
- for the descriptions hard to tell if it is applicable, besides xeno part.