INVERTEBRATA, a term commonly used in zoology to denote all those animals not possessing a backbone (e.g., insects, snails, worms), in contradistinction to the Vertebrata (q.v.), in which a backbone, or some structure representing it, is present. The animals thus brigaded together do not form in any sense a natural assemblage, but the term is none the less a very conven ient one. For the purposes of this dichotomous division the Pro
tochordata (Amphioxus, Balanoglossus and the Tunicata, qq.v.) are included in the Vertebrata, though they have no true vertebral column. (See ZOOLOGY, ZOOLOGICAL NOMENCLATURE, INVERTE BRATE EMBRYOLOGY.)