Hemichordate

Part of speech: noun, adjective

Definitions

1. A soft-bodied marine animal belonging to the phylum Hemichordata, related to both chordates and echinoderms and often living in burrows on the seafloor
2. Any member of the Hemichordata, a small group of worm-like sea creatures that share features with backboned animals and with starfish and sea urchins
3. A wormlike deep-sea invertebrate in the phylum Hemichordata, such as an acorn worm or pterobranch, with a gill-slit structure resembling that of chordates

Etymology: The name is a plain piece of scientific construction. "Hemichordate" joins the prefix "hemi-", meaning "half", to "chordate", the name for animals with a notochord at some stage of life, the group that includes vertebrates. The "hemi-" element comes from Ancient Greek "hēmi-", which descends from the same Proto-Indo-European root, "sēmi", that gave Latin "semi-" and English "semi-", so the prefix is a cousin of words like "semicircle" and "semifinal". The sense of "half" is the key to the name. Hemichordates share some features with chordates, such as gill slits and a dorsal nerve cord, but they lack a true notochord in the same form, so zoologists placed them in a group of their own, sitting beside rather than within the chordates. The word was assembled in English from these classical parts to name that intermediate group, not inherited from any ancient source.