Sounds good (whatever the phantom number might be).
I make it:
Armour Class: 17 (-1 size, +3 Dex, +5 natural), touch 12, flat-footed 14
Sure, for the basic version. When I advance one for a home campaign, it will of course also have Improved Critical (bite).
Well that (and Improved Natural Attack) goes without saying.
Filling it in a bit more...
We've basically only got its skills, feats and "Spiked Defense" special quality to figure out.
Vampire Squid
Large Magical Beast (Aquatic)
Hit Dice: 7d10+14 (52 hp)
Speed: Swim 30 ft. (6 squares)
Armour Class: 17 (-1 size, +3 Dex, +5 natural), touch 12, flat-footed 14
BAB/Grapple: +7/+17
Attack: Tentacle +12 melee (1d4+6)
Full Attack: 6 tentacles +12 melee (1d4+6) and bite +7 melee (2d8+9/18-20×3)
Space/Reach: 10 ft./10 ft. (20 ft. with tentacle)
Special Attacks: Augmented critical, constrict 1d4+6, improved grab, ramming
Special Qualities: Darkvision 60 ft., ink cloud, jet, low-light vision, "spiked defense"
Abilities: Str 23, Dex 16, Con 15, Int 10, Wis 12, Cha 11
Saves: Fort +7, Ref +8, Will 3
Skills: 20 - Listen ?, Spot ?, Swim +14
Feats: 3 - ?
Environment: Underground
Organization: Solitary
Challenge Rating: ?
Treasure: None
Alignment: Usually lawful neutral ?
Advancement: 8-12 HD (Large) 13-21 HD (Huge) ?
Level Adjustment: —
Jet (Ex): A vampire squid can jet backward once per round as a full-round action, at a speed of
120 feet. It must move in a straight line, but does not provoke attacks of opportunity while jetting.
Ramming (Ex): As a standard action, a vampire squid can swim at up to quadruple speed (120 feet) and ram a waterborne target (such as a ship or another creature). To ram, the vampire squid must end its movement in the target's space. This attack deals 2d12+9 points of damage. If the target is a creature, it can attempt either an attack of opportunity or a DC 19 Reflex save for half damage. The save DC is Strength-based.
Upon ramming a ship, the vampire squid can make a Strength check to breach its hull, which causes the ship to sink in 1d10 minutes. The break DC varies with the type of vessel rammed, as follows: rowboat DC 20, keelboat DC 23, sailing ship or longship DC 25, warship DC 27, or galley DC 30. (See Chapter 5 of the DMG for information about ships). Regardless of the check result, every creature aboard must attempt a DC 15 Reflex saving throw. Success means the creature takes 1d6 points of damage from being thrown about by the impact; failure means the creature is hurled overboard.