Vermin somehow just slipped my mind in the shock of seeing aberration! I'd go with Int - (not Int 0!) vermin myself.
OK then, I think that's enough of us agreed to make it a Vermin.
Statwise I think we can start by modifying a Medium Monstrous Scorpion, e.g. (I increased the speed from the original's 2//4, which would give 5 ft., swim 10 ft.):
Yohoia
Medium Vermin (Aquatic)
Hit Dice: 3d8+6 (19 hp)
Initiative: +0
Speed: 10 ft. (2 squares), swim 20 ft.
Armor Class: 14 (+4 natural), touch 10, flat-footed 14
Base Attack/Grapple: +2/+3
Attack: Claw +2 melee (1d8+1)
Full Attack: 2 claws +2 melee (1d8+1)
Space/Reach: 5 ft./5 ft.
Special Attacks: Snatch?
Special Qualities: Camouflage, darkvision 60 ft., hold breath (or Amphibious plus water dependency?), tremorsense 60 ft., vermin traits
Saves: Fort +5, Ref +0, Will +0
Abilities: Str 13, Dex 10, Con 14, Int -, Wis 10, Cha 2
Skills: Swim +9
Feats: —
Environment: Aquatic
Organization: Solitary or colony (2-8)
Challenge Rating: ?
Advancement: 3-5 HD (Medium); 6-9 HD (Large)
Level Adjustment: —