well with what he technically is they could have made him look like anything, but they made him look like a turtle. There are other people who will agree and disagree, but I say he is a turtle, not your typical turtle, but yes a turtle.
"Shuckle seems to be based on an endolith, an organism that lives inside porous rocks or animal shells or possibly an abalone. Fungi, also known as mold, are common endoliths; this explains why Shuckle is the mold Pokémon. It may also be based on scale insects – small, shelled parasites that produce a sweet fluid called honeydew that attracts other insects. Shuckle may have been based on a variety of mollusks, as it shares some characteristics with them. Some examples of the similar characteristics are the shell, muscular and limp-seeming feet, the use of acids to receive food or to break down obstacles, likes fermented foods, and both also live close to the water. It may also be based on turtles or tortoises, appearance-wise."
That last line looks like it was added just because. It shares no characteristics except the shell.
Its body shape, head, and limbs are nothing like a turtle, nor do I think any turtle Pokemon would ever be Bug type because they're, you know, not bugs. And like it says, Shuckle is the mold Pokemon.
Faust_8: Would you own slaves if you could? OW: If I lived on a farm or something, sure. But I have no need of slaves right now.