trichocephalus

from The Century Dictionary.

• noun A genus of nematoid worms, typical of the family Trichocephalidæ.
• noun The detached hectocotylized third left arm of the male argonaut, deposited in the pallial cavity of the female, and regarded as a parasite by Delle Chiaje, who called it Trichocephalus acetabularis, making the word a pseudogeneric name. See cut under Argonautidæ.