• Popularly known as the ‘Acorn worm’ or ‘Tongue worm’.

• Marine Hemichordate.

• It excavates ‘U’ shaped burrows in sand or sandy mud.

• Mucus emits greenish light.

• Body is divisible into Proboscis, Collar and Trunk.

• It is the connecting link between invertebrate and vertebrates.

• Body is unsegmented, soft and cylindrical.

• Trunk is divided into branchio – genital, middle hepatic, posterior part hepatic regions.

• Indirect development.

• Larva : Tornaria