Write short note on Hemichordata. 

Explanation

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 bilaterally symmetrical, triploblastic and coelomate animals.
The body is cylindrical and is composed of an anterior proboscis, a collar and a long trunk.
Circulatory system is of open type.
Respiration takes place through gills.
Excretory organ is proboscis gland.
Sexes are separate.
Fertilisation is external.
Development is indirect. Balanoglossus
Examples : Balanoglossus and Saccoglossus.