A group of spotted lagoon jellyfish (Mastigias papua)

A group of spotted lagoon jellyfish
The spotted jellyfish (Mastigias papua) belongs to the phylum cnidaria. This means they contain a specialized structure in their skin, called a cnidocyte, that the jellyfish uses to defend itself and attack its prey. The cnidocyte effectively functions as a toxin-filled pressurized harpoon that pierces into anything unlucky enough to come into contact with it.

Below you can see what a discharged cnidocyte looks like under a scanning electron microscope:

Image Source: Wikimedia Commons, User: Spaully (https://en.wikipedia.org/wiki/User:Spaully/Home)
Pretty nasty to imagine it sticking into your skin.

In addition to being weaponized, the spotted lagoon jelly are particularly interesting because they have many small mouths in what's called their oral arms. The jellyfish use their many arm mouths to eat plankton. Imagine having a mouth at the end of each of your hands—it would certainly beat using a fork.

Sources:
http://www.montereybayaquarium.org/animal-guide/invertebrates/spotted-jelly

Note: This was originally posted on my site http://www.sciphotos.com. I'm new to steem it and still learning my way around, but I plan on posting more exclusive and original content soon.