Touching a jellyfish can be a very painful experience whereas touching a comb jelly is not painful. why is there a difference?

Comb jelly does not have nematocysts.

Explanation:

Centophores (phylum Ctenophora) consists of invertebrate animals that live in marine waters. They make use of cilia for swimming, and they are the largest animals to swim with the help of cilia.

Ctenphores are popularly known as comb jellies, sea gooseberries, sea walnuts, or Venus's girdles, are voracious predators. Unlike Jelly fish(phylum cnidaria) with which they share several superficial similarities, ctenphores does not possess stinging cells, nematocysts. Instead, in order to capture prey, ctenophores possess sticky cells called colloblasts.

d they all are treatable but they never completely go away