Sketching forced me to look at the differences in detail of shape, color texture, etc. Those differences made me wonder if they were a function of environment, eg, did they blend in better where they lived with those differences? Did they prefer different places? For example, the Box Crab prefers rocks & muddy bottoms, the Kelp Crab is found in the intertidal zone, the Red Rock Crab is found on jetties, intertidal pools & under & around rocks.