Write a short note on Hemichordata.

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