From the broader portion of the planula an outgrowth arises which becomes the first tentacle of the cormus.
"Encyclopaedia Britannica, 11th Edition, Volume 14, Slice 2" by Various
In exactly the same way several individuals of certain kinds of worms are united so as to form a star-like cormus.
"The History of Creation, Vol. II (of 2)" by Ernst Haeckel