Five decades later, in light of Darwin's theory of "descent with modification", German zoologist Anton Dohrn proposed that these groups arose from a common ancestor which possessed a body plan similar to that of modern annelids with a ventral nerve cord and dorsal heart.
Cinco décadas despois, á luz da teoría de Charles Darwin da "descendencia con modificación", o zoólogo alemán Anton Dohrn propuxo que estes grupos se orixinaron a partir dun antepasado común que posuía un plan corporal similar ao dos modernos anélidos cun cordón nervioso ventral e un corazón dorsal.