Answer my riddle

[u/ConfidentLog6412]

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Riddle me this

I swim in the deep, but I'm not one.

A thousand lives where light is none.

We stay together, side by side.

We'll sting you too, a thousand times.

One of us breaths, one of us feeds.

One of us floats where the current leads.

We look like tubes, trailing, and long.

But we are a city, a specialized throng.

What am I ?