Composition: 6, Composition is nice... you avoided a static "centered" subject in favor of subjects which fall along the 3rds of the image.
Technical: 4, Fairly sharp.... could be sharper in the main subject and you might also explore color saturation.
Appeal: 4, To me, the biggest shell must be the main subject, because the rest is much smaller. Yet the really sharp focus in the picture is in the center (on the smaller shell) which confuses my eye... I want to look at the big shell, but end up being forced to look at the small one. The white crystals that surround the shells are okay in the center, but mostly show "dirt" on the right 3rd of the image.
Challenge: 5, Okay close-up. A more macro version would have focused on just a portion of the big shell and explored the textures to be found there when looking at an extreme close-up or macro.
Overall Calculated Average Score: 5, Not a bad pic... lacks a little in the technical and creative sides.