1. Any of a group of small marine animals that have some characteristics of chordates, including a notochord-like structure, and are considered to be related to the ancestors of vertebrates.
Usage: biology; zoology; technical

Examples

• Hemichordates are found in ocean sediments and are important for understanding the evolution of chordates.
• The acorn worm is a common example of a hemichordate.
• Scientists study hemichordates to learn about the early development of vertebrate ancestors.
• Hemichordates possess a structure called a stomochord that resembles the notochord of true chordates.
• These small marine creatures bridge the gap between invertebrates and vertebrates in evolutionary history.