We don't have synonyms for mastax yet — it may be a rare, specialized, newly coined, or misspelled word. The closest thesaurus entries we have are masta, mystax and mastah.
(n) :
(zoology) The pharynx of a rotifer. It usually contains four horny pieces. The two central ones form the incus, against which the mallei, or lateral ones, work so as to crush the food.
(n) :
(zoology) The pharynx of a rotifer. It usually contains four horny pieces. The two central ones form the incus, against which the mallei, or lateral ones, work so as to crush the food.