anthaceros, corrected
heard as anthaceros
spelled anthoceros
Anthoceros. The vowel joining the two halves is o.
What the ear did
It is the linking vowel of a Greek compound, the same one that joins the parts of chromosome and thermostat. It never takes stress, so it is never clearly heard.
A-N-T-H-O-C-E-R-O-S
The full entry for anthoceros covers the name itself.