Thanks for playing! Actually, we did put in code to ensure that creatures wouldn't look too much alike unless it's intentional.
Creatures have five traits that affect appearance (and many traits that don't): color, size, head shape (or lack of head), leg shape (or lack of legs), and body shape. We randomly generate creature species, and we check to see if a species is similar to (i.e., all traits are the same, or all traits but one are the same) any existing species. If it is, we don't create it.
However, that rule is broken for the poisonous species. All of the poisonous species actually look exactly like one of the edible species, except for one trait. So you'll have poisonous species which have the same head/body/legs/color as an edible species, but a different size (for instance). Or everything the same except for different colors, etc. We did this to make it more challenging to spot poisonous creatures, sort of inspired by the real-life case in nature where you have poisonous mushrooms which look similar to edible ones with a certain key feature which is different.