Still life (and still learning)

[Lindy]

I retired my D7100 and bought a new Z5. Wow, whole new learning curve.
Took this still life of shells with a Nikkor 28-75/2.8 at 50mm, 1/40s, f/18. Natural light through a window with translucent blinds, no flash. Thoughts?

 

[Needa]

Removing the background spot would help. Other than that play with the arrangement. Maybe turn 1st shell so the lines converge in the center of the others or swap it diagonally and have the dark part to the center and the line point to the negative space. I've shot dozen of shots of objects on the beach only to delete them all, so just keep at it.