Your organic intersections showed a good grasp of how the forms wrap around one another, so it was a lack of application - although in truth it's also a different context so it's not abnormal for the understanding to translate fully without a bit of help.

You can use whatever references you like - just make sure that they're all high resolution, so it's easier to identify the major elements of the given animal. Low-res reference can make things harder than it needs to be.