antoceros: is there a th in the first syllable?
heard as antoceros
spelled anthoceros
Yes, from anthos, flower. Anthoceros.
What the ear did
Many speakers flatten the th to a plain t in a fast unstressed syllable, and the spelling then follows the mouth. The th is the giveaway that the first half of the name is the same word as in anthology, a gathering of flowers.
A-N-T-H-O-C-E-R-O-S
The full entry for anthoceros covers the name itself.