Instead the terms cephalothorax or prosoma are widely used.
"Explanation of Terms Used in Entomology" by John. B. Smith
The prosoma is well developed.
"A Monograph on the Sub-class Cirripedia (Volume 1 of 2)" by Charles Darwin
I to VI, The six appendage-bearing somites of the prosoma.
"Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 3" by Various