In a species of snail, dark-shelled individuals are better hidden from bird predators in the shady forest, while light-shelled individuals are better hidden in well-lit brushy edge areas. If there were no areas of intermediate brightness in this habitat, which type of selection would act on shell color in these snails?

Disruptive selection

Explanation:

In the given question, the dark-snails and the light-snails are protected from the predator in the shady and the brushy edge areas respectively while the areas with intermediate colour will not prove beneficial to the snails and will increase the chances of the predation.

Therefore nature will select the snails which could be either the dark coloured or light coloured but not the intermediate colour of the snail. This shows that the intermediate colour will not survive whereas the extreme colour of the snail is favoured and will reproduce.

Thus, Disruptive selection is correct.

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answer and explanation;

volcanic rocks are igneous rocks which form from lava, molten rock which has been thrust out of a volcano onto the surface of a rocky body such as an asteroid, planet, or dwarf planet.  

plutonic rocks are igneous rocks which form from subterranean chambers of molten rock or magma. plutonic rocks make up the base of continental crust as well as oceanic crust. their slow rate of formation causes them to be coarse grained since there is plenty of time for large crystals to form before the magma solidifies into rock.

the textural difference is that plutonic rocks are more coarse grained than volcanic rocks. plutonic rocks are coarse grained while volcanic are fine grained ; glassey or fragmental. since fine and coarse are adjectives the decision as to whether a rock is fine or coarse grained is generally made on the bases of whether or not the individual crystals can be seen in most if the rock.