What makes a cnidarian unique?

The Word cnidarian is a very unique Word that begins with two consonants. One of only two in the entire English language that begins with 'cn' producing the same sound as the letter 'n' alone. Similar in prefix pronounciation to "gnat" or "knight".

Addition:

Cnidarians take their name from cnidocyte cells, most of which contain a nematocyst - a stinging cell that injects a toxin. Only Cnidarians have nematocysts.

All cnidarian forms are either a sedentary polyp or a floating/free-swimming medusa. They have no excretory or respiratory system.