Why Hemichordates are not placed under Chordates?

Hemichordates don’t have a notochord or a post-anal tail in their body, which is a differentiating feature in the chordates. Earlier, the hemichordates were placed among the chordates but due to the absence of any type of backbone or chord, these were removed from the group.

The hemichordates are marine animals and have triploblastic bodies. They are also known as acorn worms.

There are distinct animals with distinct structures and forms. Till now, a million species of animals have been introduced, and the urge for classification becomes all the more essential. The classification also assists in allowing a systematic position for newly introduced species. Animals have definite shapes and sizes. They are unbranched except for the sponges. Animal organs are generally internal, e.g., liver, heart, kidney, lungs, brain, stomach, etc. 

The growth of an animal’s body is limited, and it stops long before death. The growth regions are not localized. They can move bodily from one place to another. They have sense organs, nervous systems, and excretory organs. There are different Phyla such as Porifera, Cnidaria, Ctenophora, Platyhelminthes, Nematode, Annelida, Arthropoda, Mollusca, Echinodermata, hemichordate, and Chordata. Let us have an overview of Phylum Hemichordata.