word-forming element denoting requests and classes in zoology, from Latin -acea, neuter plural of -aceus "belonging to, of this nature of" (increased from adjectival suffix -ax, genitive -acis); neuter plural because of a presumed animalia, a neuter plural noun. Therefore, crustacea "shellfish" tend to be *crustacea animalia "crusty pets." In botany, the suffix is -aceae, from fem. plural of -aceus, with regards to Latin plantae, that will be a fem. plural.