I believe the dungeons down there have lots of alcoves, our DM modified the map and knocked out the alcove walls in their areas.
If you don't want to mess with actual girallion stats, here is an alternative from d20 arcana (in the d20 modern srd if you want it for free)
Grendelspawn Hunter medium size, CR 6.
They even have a huge queen.
Grendelspawn
Grendelspawn hiss and growl but seem to have no language of their own.
Species Traits
Grendelspawn have the following traits:
Acid Spit (Ex): Grendelspawn can spit acid up to 20 feet away as a ranged touch attack; if the acid hits, it deals 2d6 points of acid damage per round until it’s washed off with at least a gallon of water (a full-round action) or until 1 minute passes. A grendelspawn hunter can spit acid twice per day; a grendelspawn queen can spit acid at will.
Rage (Ex): A grendelspawn that takes damage in combat flies into a berserk rage the following round, clawing and biting madly until either it or its opponent is dead. An enraged grendelspawn gains +4 Strength and +4 Constitution, and it suffers a –2 penalty to Defense. The creature cannot begin or end its rage voluntarily.
Scent (Ex): This ability allows the grendelspawn to detect approaching enemies, sniff out hidden foes, and track by scent.
Keen Sight (Ex): Grendelspawn have darkvision with a range of 60 feet and low-light vision.
Grendelspawn Hunter
Hunters tend to travel in small packs of three to six. Though only marginally intelligent, they often display the cunning common to many predators.
Grendelspawn Hunter: CR 6; Medium magical beast; HD 9d10+27; hp 76; Mas 17; Init +2; Spd 40 ft., climb 20 ft.; Defense 18, touch 12, flat-footed 16 (+2 Dex, +6 natural); BAB +9; Grap +14; Atk +14 melee (1d6+5, bite) or +11 ranged touch (2d6, acid spit); Full Atk +14 melee (1d4+5, 2 claws), +12 melee (1d6+2, bite) or +11 ranged touch (2d6, acid spit); FS 5 ft. by 5 ft.; Reach 5 ft.; SQ acid spit (2/day), rage, scent, keen sight; AL queen, master; SV Fort +9, Ref +8, Will +4; AP 0; Rep +0; Str 20, Dex 15, Con 17, Int 3, Wis 12, Cha 11.
Skills: Climb +13, Listen +6, Spot +6, Survival +5.
Feats: Combat Reflexes, Multiattack, Track.
Rage (Ex): When raging, a grendelspawn hunter gains 18 hit points. Its other statistics change as follows: Mas 21; Defense 16, touch 10, flat-footed 14; Grap +16; Atk +16 melee (1d6+7, bite); Full Atk +16 melee (1d4+7, 2 claws), +14 melee (1d6+3, bite); SV Fort +11; Str 24, Con 21.
Possessions: None.
Advancement: 10–15 HD (Medium); 16–27 HD (Large).
Grendelspawn Queen
Grendelspawn queens are generally solitary, although sometimes a small cluster of them will cooperate long enough to protect a joint clutch of eggs. They have a ruthless intellect devoted solely to the protection of their progeny.
The grendelspawn queen gains the following additional special qualities:
Improved Grab (Ex): To use this ability, a grendelspawn queen must hit with its tentacle slam. If it gets a hold, it can constrict (see below).
Constrict (Ex): A grendelspawn queen deals automatic tentacle damage with a successful grapple check against creatures smaller than itself.
Grendelspawn Queen: CR 12; Huge magical beast; HD 14d10+70; hp 147; Mas 21; Init +0; Spd 20 ft.; Defense 22, touch 8, flat-footed 22 (–2 size, +14 natural); BAB +14; Grap +30; Atk +20 melee (2d6+12, bite) or +12 ranged touch (2d6, acid spit); Full Atk +20 melee (2d4+8, 2 claws), +18 melee (2d6+4, bite), +18 melee (1d6+4, 2 tentacle slams) or +12 ranged touch (2d6, acid spit); FS 15 ft. by 15 ft.; Reach 10 ft.; SQ acid spit (at will), rage, improved grab, constrict, scent, keen sight; AL eggs; SV Fort +14, Ref +9, Will +5; AP 0; Rep +0; Str 26, Dex 10, Con 21, Int 13, Wis 12, Cha 15.
Skills: Hide –8, Intimidate +15, Listen +14, Spot +14.
Feats: Blind-Fight, Combat Expertise, Frightful Presence, Multiattack, Power Attack.
Rage (Ex): When raging, a grendelspawn queen gains 28 hit points. Her other statistics change as follows: Mas 25; Defense 20, touch 6, flat-footed 20; Grap +32; Atk +22 melee (2d6+15, bite); Full Atk +22 melee (2d4+10, 2 claws), +20 melee (2d6+5, bite), +20 melee (1d6+5, 2 tentacle slams); SV Fort +16; Str 30, Con 25.
Possessions: None.
Advancement: 15–32 HD (Huge); 33–42 HD (Gargantuan).