sexdigitist

from The Century Dictionary.

• noun A six-fingered or six-toed person; one who or that which exhibits or is characterized by sexdigitism.

from the GNU version of the Collaborative International Dictionary of English.

• noun One who has six fingers on a hand, or six toes on a foot.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun rare One who has six fingers on a hand, or six toes on a foot.