There's really two things that I want to bring up here. The first is that the Anatomically Correct series of questions has been flooded with recent questions about various creatures. This is kind of humorous because I was looking into it, and TrEs-2b, the founder of the series, mentions on the Anatomically Correct Slime question (#43) that it was running out of creatures. For reference, we're on #117 last count, and that number will be growing rapidly. This is because if we don't set hard and fast rules as to what is allowed and what isn't, then literally all of science fiction, fantasy, myth, legend, and what-have-you becomes fair game for the Anatomically Correct series, so it will never run out of creatures so long as someone has access to Google.
And I would like not to stop this, but rather to gently apply the brakes and perhaps nudge the wheel a bit. I love the concept of the Anatomically Correct series, because it introduces a monster and then says, 'Okay, but what if this monster was real?", or a fantasy race, or what have you. Then it's a fun exercise putting together the jigsaw of components that allow you to come as close as possible to the target creature, all while staying within the realm of biology. But if we just allow everything, than we run the risk of over-saturating the field. Furthermore, some of the submissions of that 117-item list (as of the time this is being brought up) isn't exactly worthy of the list, so I propose that we implement a more rigid system into place such that all the coming questions in the Anatomically Correct series need not run the risk of downvotes, getting closed, or just an overall lack of interest and answers.
The second thing I want to bring up is that one of the more recent submitters to the series has been insisting on all the creatures evolving naturally. That is certainly a bonus if we can create a creature that can naturally evolve, but that is also horribly limiting in it's own way. A lot of creatures submitted to the list where not created with the intention that they could evolve, they were created to look cool or to be intimidating, and have no business evolving in the first place. Insisting on evolution is a limiting factor when it comes to anatomy, and we can get a lot better answers if we remove that limit.
Here is a short and rough list of conditions that I suggest. The first few have been taken from TrEs-2b's original post in the Meta, and then I've added a few myself.
Conditions for Anatomically Correct:
Generalizations are forbidden. A creature must be described as such that a coherent answer can be provided. (Using just 'Vampire' as a description is no good. Something more akin to 'Vampire which is weak to sunlight and feeds on blood' is better.) Links help, but they should be an addendum, not a substitute, for descriptions.
On descriptions: It should be a clear and thorough description of all the animal's qualities, as well as signature behaviors of said animal. To borrow the phrase 'We're willing to help, but we will not invent the creature and summon it into this world for you'. Pictures help, but they should be an addendum, not a substitute, for description.
Using previous questions under the 'Anatomically Correct' label as an example of why your question isn't violating the rules is not a valid defense. Those question are the exceptions that have been grandfathered in, they are not the precedent.
One that I propose adding:
The only requirement for the answer is to be an anatomically correct creature of the question, or at least as close as can be gotten using the current understanding of biology. Magic or handwavium of any sort is forbidden. Explanation of the evolution of such a creature is nice, but not required. This is to give maximum room for potential answers.
Variations of creatures which already exist in the series should be discouraged unless they are wholly distinct, i.e. if we have a working answer for Elves, asking a new question about dark elves or water elves should be discouraged unless they are functionally different in a lot ways. (I.e. if your water elves can actually breathe water and have other aquatic features, that's fine. If they only have fin-like hands and feet, that's not quite unique enough.)
Characters and creatures that were not intended to be meaningful living creatures with the use of magic, cartoon physics, and / or handwavium should be treated very, very carefully. If you're going to ask about them, make the necessary adjustments in order for them to be meaningful living characters. (For instance, if you wanted to make an 'Anatomically Correct Mickey Mouse', first describe him as close to a real creature as possible, i.e. humanoid creature with mouse-like features including ears and a tail, 3-foot tall body. Don't just post a 2D cartoon picture.) Creatures that have been given power which are biologically impossible should be summarily rejected from the series.
An 'Anatomically-Correct' tag should be created and applied to all questions within the series, in addition to the titles. A question that doesn't meet these guidelines should not be closed out of hand unless it also violates this site's other guidelines, such as being a duplicate or being too vague. The idea is that, while we want to keep the Anatomically Correct series exclusive, we don't want to prevent other questions which don't make the cut, thus providing the tag.
Lastly, (and this is not a suggested guideline, it's just a faint plea from me) please try and help to make sure that this tradition is taken with the respect it deserves. I've been on Worldbuilding for less than a year right now, but this is honestly one of my favorite parts of it, and I would really like for it to continue. If you have a favorite monster or you're worldbuilding for a story and you want to use this question, great! Please put it out, I'll gladly read it and try to come up with a creature that works, alongside the other members of this sight. But if the creature you have in mind is just one of idle curiosity which doesn't really fit, maybe consider just asking it as a normal question or saving it for later when you're more interested.