Phylum Hemichordata: These animals are also called as Acorn Worms. They were initially grouped under Phylum Chordata. But, research has proven that none of these organisms does not have a post-anal tail or even the notochord, which is a distinguishing feature of chordates. Hence, these animals have been given a separate phylum, called the Hemichordata.

• 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 organ-system level of organisation.
• They are cylindrical [bilaterally symmetrical], triploblastic, coelomate animals.
• The body is Circulatory system is of open type.
• Respiration takes place through gills.
• Excretory organ is present.
• Sexes are separate. Fertilisation is external. Development is indirect.
• Examples: Balanoglossus and Saccoglossus.

Classification of Phylum Hemichordata

Phylum Hemichordata is again divided into two classes:

• Enteropneusta: This class includes acorn worms. They have a vermiform body and are found on sandy beaches near seas in warm climates.
• Pterobranchia: They have a tube-dwelling and live in deep sea waters. They are bottom dwellers who attache to other organisms for their survival.

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By Team Learning Mantras