Hemichordates

Part of speech: noun

Definitions

1. A group of marine invertebrates that are related to vertebrates, characterized by a notochord and dorsal nerve cord, which include species such as acorn worms and lancelets
2. Invertebrates that possess features similar to those of vertebrates, exhibiting a simple body structure and segmented body plans, primarily residing in marine environments
3. Organisms that form a phylum distinct from other chordates, known for their developmental stages and morphological traits that showcase evolutionary links to higher vertebrates

Etymology: Hemichordates are a phylum of marine animals, such as acorn worms, whose name combines two elements. The first, "hemi-", comes from Ancient Greek "hēmi-", meaning "half", and is the same prefix found in words like hemisphere. The second, "chordate", refers to the broader group of animals that have, at some stage of life, a notochord, a flexible rod that runs along the body and gives the group its name. The name is therefore a literal description: these animals were classed as "half-chordates", sitting close to the chordates but lacking some of their defining features. The Greek prefix was joined to the established zoological term in English, following the common scientific habit of building names from classical roots. Note that the plural "hemichordates" is simply the regular plural of "hemichordate".