Why might natural selection influence the lengths and widths of brachiopods?

Question

Brachiopods are marine animals.

Answer 1

Natural selection will influence any characteristic that has survival value. If a certain length or width helps the brachiopod survive to reproduce when others die, then that length or width is more likey to be passed to the next generation and to become more widespread in the population.

For instance:
-- a narrow width might allow a brachiopod to hide in crevices and avoid being eaten
-- a greater width might make the brachiopod harder to swallow for some organisms
-- a greater length might make the brachiopod faster

and so on ...

Answer 2

This is for school, isn't it?