It does, but isn't clearly mentioned in the datasheet. Port A is the ADC 'port'.
It shares most of the pins of Port C (some packages have two extra ADC pins though). I think Atmel uses the Port C moniker for the 'digital' inputs on those pins, and Port A for the analog input. I agree it is confusing.
From page 251 of the datasheet:
"The ADC is connected to an 8-channel Analog Multiplexer which allows eight single-ended voltage inputs constructed from the pins of Port A."
As such, my guess is that Port A represents the internal 8 connections to the ADC.
I just had a look at the Atmega16 Datasheet (http://www.atmel.com/Images/doc2466.pdf). This does have Port A dedicated to the ADC. As such, I think the CPU core is similar but the external pins are multiplexed. I guess for the Atmega8 series they should have dropped the Port A moniker completely to avoid confusion, or maybe they did and the ADC chapter in the datasheet is a typo as you mentioned in the comments.