(ˌɛpɪˈθiːkə) n, pl-cae (-siː) (Zoology) the outer and older layer of the cell wall of a diatom. Compare hypotheca[C19: from epi- + theca]
epitheca
epitheca
[¦ep·ə′thē·kə] (invertebrate zoology) An external, calcareous layer around the basal portion of the theca of many corals.A protective covering of the epicone.The outer portion of a diatom frustule.