This list of mythical creatures that begin with this letter and I am constantly gathering information from each continent, and is continually being updated.
Ichthyocentaur (Greek)
In later Greek periods into the Roman period Tritons were depicted as ichthyocentaurs, i.e., merman with a horse's forelegs in place of arms. The earliest known examples are from the 2nd century BC. The term "Ichthyocentaur" did not originate in Ancient Greece, and only appeared in writing in the Byzantine period (12th century); "Centaur-Triton" is another word for a Triton with horse-legs.
Besides examples in which the horse-like forelimbs have been replaced by wings, there are other examples where the forelegs have several clawed digits (somewhat like lions), as in one relief at the Glyptothek in Munich, Germany. A Triton with a lower extremity like a lobster or crayfish, in a fresco unearthed from Herculanum has been mentioned.