Very, very formal, if that's what you were aiming for. I like it that way. To make it more informal, you could make the shell imperfect: by rotating it slightly,and making it not quite so perfectly in the corner. It might be fun to experiment.
This is a very good image. The ROT is perfect for this challenge. I have noticed that many images are close but do not follow it in this rule. This image is one of them. That is not necesarily bad given the nature of this challenge. However, I wish your subject in this case would have been placed a little further left and slightly higher.
Kewl shot, I love the texture of the background and the composition is spot on. Now you got me craving for paua fritters. Something I haven't had for years! (9)
One of my favorites in this challenge! Wonderful texture -- you can almost feel it. Nice focus and contrast on the shimmering colors of the shell. Great job!