It depends on what you mean by *Dark Net*.  There are several TLDs used for different systems of anonymous internet access.

Here are a few:

 - `.bit` used by <a href="https://zeronet.io/">Zeronet</a>
 - `.i2p` used by the <a href="https://geti2p.net/en">Invisible Internet Project</a>
 - `.loki` used by <a href="https://loki.network/">Loki</a>
 - `.onion` used by the <a href="https://torproject.org">Tor Project</a> (included for completeness)

Also, there are systems that don't use domains at all or, at least, not as we know them.

I'd be surprised if there aren't many others too.