Advanced Race Builder. Since this is absurd let's go crazy and make 'em 20 points at the edge of balance.
Here is my take:
Crab People (Looks like Crab, Walks like People)
Adjusted 20 Race Points
+3 Monstrous Humanoid
+0 Aquatic Subtype
+0 Size: Medium
+0 Speed: Land 30'
+4 Abilities: Advanced. +2 STR, DEX, CON, +4 INT, -2 WIS
+2 Amphibious: Can breathe both air & water
+2 Claws 1d4 Primary Natural Weapons x2
+0 Darkvision: 60'
+2 Deepsight: Underwater Darkvision 120'
-1 Delicious: -2 Escape Artist/CMD vs Bite (-4 if lemon or butter is used)
-1 Light Sensitivity: They do have those little black pearls for peepers.
+4 Lucky, Greater: +2 Racial Saves All. They need all they can get.
+0 Sexual Dimorphism: Males=+2STR, -2WIS. Females=+2CHA, -2CON
-1 Shattered Soul: Harder to Resurrect
+0 Speak with Avians: It was free... guess the Crab People like Seagulls, Ospreys, Penguins, etc.
+3 Spell Resistance, Greater: SR=CL+11
+2 Swim: Swim Speed = 30'. +8 Swim Checks.
+1 Water Sense: Blindsense in Water 30'
Starting Languages: Aquan, Undercommon.
Their mouths evolved to enable speech, and thus lost their bite potential. It'd have taken points away from the build and emphasis for the implied hint towards focus on the Claws in feats.
Monstrous Race Unlocks crazy awesome options related to grappling, multiple limbs, grasping and mobility, but really escalates the character beyond scale.
Fluff:
Having evolved from arcane laboratories and cultist circles, the Crab People found themselves able to breed true to create offspring and gifted with the magical enhancement to have an edge over wild species in their environment. They have adapted to subterranean living but are able to flourish in cavernous systems, particularly in the darklands and can tolerate exposure to sunlight with adaptation.
Being the offspring of both Arcane tinkering and the get of eldritch rites invoking the Dark Tapestry, the Crab People are insular and clannish in nature, acknowledging the value of trade and interaction with Intelligent races, but always wary of ever being exploited again, which in their worldview is a matter of when, not if. Morality to them is a matter of perspective and necessity, not values. Their insular nature and lack of assimilation with the established cultures on Golarion has led to a racial tendency towards gullibility when made to interact, reflecting the birthing wounds to their racial psyche.
Physically they have been adapted for amphibious function, and have the potential to rival the Sahuagin should they ever amass the numbers and organize massed communities. Being a Monstrous Humanoid with claws, most Humanoid equipment have to be modified or customized for usage by the Crab People, with the most common form that of grafting said equipment to their carapace of limbs. A cosmetic accessory typically taken for fashion as much as necessity is a sunshade or visor, usually made for shellfish or coral to protect their eyes when they venture into well-lit environments.
Odd to note, but they have only one standing rivalry in their hostile environment: the elusive, but devious Underwear Gnome, a perverted derivative offshoot of depraved Svirfneblin.
If there are no limits, why not just give brawler class levels to a karkinoi?
http://paizo.com/pathfinderRPG/prd/bestiary4/karkinoi.html#karkinoi
Well that crab just pinched my balloon...