By some they are classed with the Scolecida in the sub-kingdom Annuloida.
"The New Gresham Encyclopedia" by Various
SCOLECIDA, absence of secondary sexual characters in, i.
"The Descent of Man and Selection in Relation to Sex" by Charles Darwin
SEVENTH STAGE: +Soft Worms (Scolecida)+.
"The History of Creation, Vol. II (of 2)" by Ernst Haeckel