Min Seg (Mega 2560) Connects to Mac as tty, Connects to Arduino IDE as cu Only

I own a Min Seg.
My Min Seg model is built on an Arduino Mega 2560.

I have a Macbook running OS X 10.10.3 (Yosemite)

When I connect the board to the Macbook,
using either of the Macbook's two USB 2.0 ports,
using either of two USB A to B cables,
the board lights up, but I am unable to connect
to the tty device using the Arduino IDE.

Tools --> Port offered:

/dev/cu.Bluetooth-Incoming-Port
/dev/cu.Bluetooth-Modem
/dev/cu.usbmodem621 (Arduino Genuino Mega or Mega 2560)

I was expecting to also see:

/dev/tty.usbmodem621 (Arduino Genuino Mega or Mega 2560)

If I unplug the board, the third listed option
from Tools --> Port disappears, as expected.

I opened the System Information utility application.
USB --> USB Bus -->Arduino Mega:

  Product ID:    0x0042
  Vendor  ID:    0x2a03
  Version:	    0.01
  Serial Number: 75435353038351316281
  Speed:         Up to 12 Mb/sec
  Manufacturer:  Arduino Srl
  Location ID:   0x06200000 / 3
  Current Available (mA): 500
  Current Required  (mA): 100

I used the Sparkfun Terminal basics to check for the device.
I used the Terminal utility application.

ls /dev/tty.* offered:

/dev/tty.Bluetooth-Incoming-Port
/dev/tty.Bluetooth-Modem
/dev/tty.usbmodem621

screen /dev/tty.usbmodem621 9600 offered a successful connection.
[A white screen, which allowed for exit using Control+a followed by Control+/]

I have begun to try other means.
The majority of these means were sourced from other threads, such as here.

Mathworks Simulink states that a cu device is expected,
rather than a tty, when setting connection options.

I installed the FTDI drivers.

I ran the following code in the terminal: sudo nvram boot-args="kext-dev-mode=1"

Is an alternative driver worth attempting, such as that listed here?

Answer: Answer granted here.

In short, the starter guide is written incorrectly. A cu address should be used rather than a tty address.