The magic translator provides /dev/fd.
$ showtrans /dev/fd
/hurd/magic --directory fd
The /dev/fd directory holds the open file descriptors for your
current process. You can't see them with ls -l /dev/fd/ but you can see them
individually like this:
$ ls -l /dev/fd/0
crw--w---- 1 bing tty 0, 0 Nov 19 18:00 /dev/fd/0