Mac Arduino IDE Connection to Min Seg (Mega 2560). No tty
What you are seeing is normal.

In BSD (which is the OS that Mac OS is based on) a serial port has two distinct devices for two distinct roles.

The tty, or TeleTYpe interface is used for incoming connections, be that from a modem, serial terminal, whatever. You would normally run a process called getty on it to present a login prompt.

The cu, or Call Unix interface is used for making outgoing connections to other devices. Traditionally that was mainly other Unix servers through modems. Nowadays it includes many other devices such as an Arduino.

The theory is that when you try and initiate an outgoing connection through the cu interface it first checks that no-one is connected in through the tty interface and if the serial port is available it disables the tty interface so the listening getty process doesn't interfere with your call. Also the tty and cu interfaces deal with the modem control lines differently.

The Arduino IDE is merely honouring that system by only offering you the outgoing device in the port list. As far as the Arduino communication is concerned there should be no difference.