Analyze for mollusks and echinoderms, what are the advantages and disadvantages of having a shell or spiny skeleton?

SHELL:
- Advantage: the shell can be a good protection against predators and it protects mollusks' soft body.
- Disadvantage: the shell can be heavy and a lot of energy is needed to move it which can slow down a mollusk

SPINY SKELETON:
- Advantages: spiny skeleton serves as a protection against predators.
- Disadvantages: in some species, spine skeletons do not allow for much body flexibility.

The answer is atmosphere. there are four spheres of the earth: 1. geosphere (from greek word 'geo' = ground), 2. hydrosphere (from greek word 'hydro' = water), 3. biosphere (from greek word 'bio' = life), and 4. atmosphere (from greek word 'atmo' = air). a magnetosphere is a region of space around astronomical objects controlled by the magnetic field of that object. through the process of elimination, since lightning is present in the air, it can be found in the atmosphere.