I rec'd a separate W2 from Aetna Ins. for Short Term Disability rec'd on Maternity Leave. Is this income taxable? Do I need to enter it as add'l income? As another W2?

It depends, based on the way it was reported to you.  

If you receive a W-2 for a third party sick pay, with no amount in box 1 for wages and the income is reported in box 12 with code of J: Non-taxable sick pay is not subject to taxation. It does not need to be reported on your income taxes. Your employer was required to generate a W2 with the figure, which is why you received it. So basically you do not need to file this return, per IRS.

If you and your employer share the cost of a disability plan, you are only liable for taxes on the amount received due to payments made by your employer. 

• Report your W2 using these steps- Federal Taxes > Wages and Income >Wages and Salaries

See the following TurboTax article for additional information:  Are Short Term Disability Claim Payments ... - TurboTax - Intuit

Related information:

• Is disability income taxable?