If you allow me to talk from memory and a very little digging in my Web 
Browser Archives, may I say you are very right for looking into this.

First, below is text copied from an ATMEL Application Note PDF file 
without a number, but with the shown title. There are many others like 
it on the same topic.

Application Note

Migrating from RS-232 to USB Bridge
Doc Control
  Purpose of Modifications
  Creation date
24 Nov 2003
22 Dec 2003
  Universal Serial Bus Specification, revision 2.0
  Universal Serial Bus Class Definition for Communication Devices, 
version 1.1
  USB CDC demo firmware
  USB: Universal Serial Bus
  CDC: Communication Device Class
  ACM: Abstract Control Model
  VID: Vendor Identifier
  PID: Product Identifier

The Arduino shows up as "/dev/ttyACM(X) when attached to Linux via USB, 
and behaves just like a terminal port. It does not have all 8 serial 
lines active , but does use 2 simulated flow control lines to switch the 
Arduino into program mode.

Going further to confuse and encourage you, "Bluetooth" wireless devices 
were originally invented to remove the wires of the PC serial ports. And 
seem to parallel the USB development path.

Look for /dev/ttyACM0. Add your user to the group "dialout" IIRC. And 
have a lot of fun with Arduino and Linux.

admin at lctn.org wrote:
> I have a little kingdel box that has 5 actual, 9 pin serial ports. I am
> working with arduino and need my active usb port to show up as a com
> port, but it doesn't.
> ls /dev/tty* does not list any usb devices. Is there a way to make the
> usb port a com port in this case?
> Ubuntu 18.04.3 LTS
> Raymond Norton
> 952.955.7766
> _______________________________________________
> TCLUG Mailing List - Minneapolis/St. Paul, Minnesota
> tclug-list at mn-linux.org
> http://mailman.mn-linux.org/mailman/listinfo/tclug-list