A member of the phylum Hemichordata, marine animals that share some characteristics with chordates but lack a true notochord. They include acorn worms and pterobranchs, possessing pharyngeal gill slits and a dorsal nerve cord in some regions.
From Greek 'hemi' meaning half and 'chorda' meaning cord, literally 'half-chordate.' Named in the late 19th century when biologists recognized these animals as having some but not all chordate characteristics, representing a possible evolutionary link.
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