3d flower diffuser

I have created a prototype but would like help in creating a more attractive flower design diffuser container.

Requirements:

1. It will be 1 or 2 part unit curved top part of the design with a flat back. but must be able to open and close. I am open to other ideas on the best way for this to be orchestrated.
2. It may be possible for piece 1 to twist & screw onto piece 2 using the piece in the centre of the design as a bolt .
3. The diffuser will need to be able to hold pieces the size of rice grains whilst being still allowing for a water to be able to flow through the vents.
4. The size/ diameter of this object would be around 14cm Circumference x 2.0cm(depth) 

Additional Images: 

1. https://www.dropbox.com/s/63vlms38n1axe82/3d%20flow%20vents.jpg?dl=0
2. https://www.dropbox.com/s/p5mhky4qstfw7we/Arctic-Cat-Screw-on-Vented%20P12345266.jpg?dl=0
3. https://www.dropbox.com/s/ng0rhaqft2n45la/screw.jpg?dl=0
4. Design from Crystal: https://www.dropbox.com/s/ek3gsc63hzbm3pq/3d-flower-diffuser-v05-symmetric.stl?dl=0