A question on prestige casting classes.

[Calemyr]

This is something I've been wondering about ever since I first learned of prestige classes. Prestige casting classes like Archmage and Thaumaturgist are listed with (+1 Existing Class) as class feature. Now I know this means you gain spells and they improve as though you'd gained a level in that class, and that you don't gain new features related to that class, but just where "can" becomes "can't" is unclear to me. Is there an official ruling on these issues?

Familiars: If a wizard becomes an Archmage, does his archmage levels help improve his familiar?

Animal Companions: What of druids who take prestige caster classes? Do their animal companions continue to improve?

Turning: If a cleric takes a prestige caster class with (+1 divine caster class) on it, is their effective level for turning improved as well?

Domain Powers: Very few do, but for those few (such as the Death Touch power), does that improve?

This is probably a dumb question to ask, but it's just been something I've always been curious about. Thank you for any answers you can share with me.

[Assassinfox]

Dunno about domain powers, but I know familiars, animal companions, and turning don't improve unless the PrC says otherwise.

[Khantalas]

Class features do not improve. Only spellcasting does. You gain more spells per day, but nothing else the old class has.

Yeah, and new spell levels.