The shell covering a seed is sometimes called a hull.
Seed coat.
the valence shell
germination
linseed.
Burr
seed leaves
To effectively shell sunflower seeds, first crack the shell with your teeth or a nutcracker. Then, use your fingers to remove the seed from the shell. Repeat the process for each seed.
gladius
Aril, testa, hull
An egg
It protects it's seed with the outer shell covering.
The Plastron - is another name for the underside of the shell !