Phylum Hemichordata was earlier considered as a sub-phylum under phylum Chordata. But now it is placed as a separate phylum under non-chordata. This phylum consists of a small group of worm-like marine animals with the organ-system level of organization. They are bilaterally symmetrical. triploblastic and coelomate animals. The body is cylindrical and is composed of an anterior proboscis, a collar and a long trunk (Figure).
The circulatory system is of open type. Respiration takes place through gills. The excretory organ is probosci’s gland. Sexes are separate. Fertilization is external. Development is indirect.
Examples: Balanoglossus and Saccoglossus.