What is a jellyfish invertebrate or vertebrate?

A jellyfish is an animal in the cnidarian phylum along with anemones and other creatures with nematocysts (stinging cells). Some are tiny and some can grow very large (i.e. the lion's mane jelly). All jellyfish have nematocysts, however some jellies possess very weak nematocysts meant for tiny prey like copopods. The stinging cells in these jellies are generally not felt by humans with the exception of sensitive skin. Cnidarians do not possess brains, but some have eye spots for sensing light.