What exactly do you mean by "hard shelled?"
no, because it has a hard outer shell
Its hard to know without seeing a picture, but this could be describing a wolf spider, but its more likely an orb spider based off the limited information.
It is hard to know for certain without seeing a picture. However, this spider is most likely the Enoplognatha ovata.
Reptile eggs are soft-shelled so that the babies can break out of the shells. Bird eggs are hard-shelled, because baby birds use their beaks to crack the shells of their eggs, but since reptiles don't have beaks to use to break their shells, their eggs have to be soft-shelled.
It really does depend on the type of spider you get bitten by but in most cases the answer is no
A turttle.
There are many such hard shelled insects, mostly beetles.
It is hard to identify a spider without knowing how big it is, where it was found, its overall body shape and other characteristics. This could be a common house spider, a wolf spider, or a garden orb weaver.
A hard shelled sea creature is the barnacle.
no, because it has a hard outer shell
Platypus eggs are not hard-shelled, like birds' eggs. They are soft-shelled and leathery.
Your description could fit hundreds of different species, but if the spider is fairly large and has a "flat body" it might well be a Huntsman spider, of which there are several kinds. Try searching in Google for "huntsman spider" and then looking at the images that come up.
no
Its hard to know without seeing a picture, but this could be describing a wolf spider, but its more likely an orb spider based off the limited information.
bugs
yes, hard shelled tacos are the traditional mexican ones, soft shelled tacos are technically not even tacos but burritos or enchiladas instead
Nuts are a hard shelled fruit.