What is Phylum Hemichordata ?
The name "hemi"; (meaning "half") provides a clue to these animals, which have some of the features of chordates, and some features that are characteristic of the Echinoderms. They are commonly known as the "acorn worms"; because of their acorn-shaped proboscis. These animals burrow into the sand or mud in the sea, and can grow to 2.5 meters in length. This is a very small group of animals, including only about 90 species altogether.