[3.5] Racial Ability DCs and HD

[Thurbane]

Do racial abilities that have a save DC based on Hit Dice improve with class levels, or only through racial HD? In particular, the following aiblity of the Marrulurk:

Nauseating Breath (Su): Once per day, a marrulurk can breathe a 10-foot cone of nauseating gas as a free action. All creatures except other marrulurks within the area must succeed on a DC 13 Fortitude save or be nauseated 1 round. The save DC is Constitution based.

The Marrulurk has 3 RHD and Con bonus +2, so the formula is the standard 10 + 1/2 HD + ability mod (10+1+2=13). If you could please provide quote for sources on the ruling?

Thanks - T

[kitep]

I found this in the Rules Compendium, p22, under "Breath Weapons"

SAVES AGAINST BREATH WEAPONS
    Breath weapons that deal energy damage allow a Reflex save
for half damage (DC 10 + 1/2 breathing creature’s racial HD
+ its Con modifier; the exact DC is given in the creature’s
descriptive text). Some breath weapons allow a Fortitude
save or a Will save instead of a Reflex save. In many cases,
a creature that succeeds on its saving throw against such a
breath weapon suffers a reduced effect.
    Creatures are immune to their own breath weapons.

Nauseating is not energy, but unless someone finds something better, it looks like it's racial HD only for this particular ability.