What Am I?

You will find me in the deepest parts of the ocean,

in freshwater and terrestrial destinations.

Scientists have estimated about

120, 000 of me still contentedly living.

I normally eat krill and other trivial particles.

I have a hard shell like protection to defend my back from

predators.

I have been known to be extremely ugly by judgemental

fishermen and scientists.

If it wasn’t for me the ocean would be a different place.

What Am I?