That looks great, and so do those skills and feats!
What do you think of adding tremorsense to these, like some other burrowing critters? (There's an odd split on that, but I thought I'd throw it out there.)
Its skill modifiers are horrid. Are any racial bonuses warranted? Reallocate Listen and Spot ranks to the other skills, since tremorsense gives 'em a good chance of locating opponents?
Should we give it extended reach with tentacles?
Organization: Solitary, pair, or excavation detail (3-4)?
Advancement: 11-20 HD (Huge); 21-30 HD (Gargantuan)?