Hemichordata Syllabification: (Hem·i·chor·da·ta)Pronunciation: /ˌhemikôrˈdātə/ ZoologyDefinition of Hemichordata a small phylum of marine invertebrates that comprises the acorn worms. Origin:modern Latin (see hemi-, Chordata)Hemichordata in other Oxford dictionaries Definition of Hemichordata in the British & World English dictionary