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).
Fig: Balanoglossus
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.
