Class Crustacea
Order Eupausiacea
Over 90 different species.

It looks like a shrimp. Ironically, this is it's distinguishing characteristic. If you are a serious biologist, you might note that shrimp have ten legs, while krill have 12 to 16.

Everything bigger than a krill eat krill (Krill are part of the famous plankton you hear so much about). Krill range from 10 to 150 millimetres, and thus some of them are indeed big enough for humans to catch with nets. If humans do go after krill, they must freeze it immediately, as krill turn poisonous at room temperature.

I like the word krill. (Roll the R)

Krill have light making organs. 10 of them, for each krill. Just thought I'd mention it.
A group of krill is known as a swarm.