Little eggs that hatched a thing that looked like a.....?

Question

i was at a cave for vacation and i bought something from a gift store that you put in a glass jar and fill it with room temp water and it hatches a creature like a trilobite, i did the instructions and something hatched it does look like a trilobite and it also looks like a horse shoe crab its about nickle size and its really cool what is the creature that is in the glass jar?

Answer 1

Horseshoe crabs are marine animals so it's unlikely any would survive in a (freshwater) cave or a jar filled with tap water.

There's no way to know without a picture. Also it would help if you could tell us the location of the cave where you bought the jar.

ADDED: I wish I could help out but I have no idea what this critter might be. Perhaps you could contact the gift shop and ask what the eggs were they sold to you.

In the meantime, here's  a link to pictures of cave crustaceans.