The gills were at first external, like the gills of many Chaetopods at the present day.
"Form and Function" by E. S. (Edward Stuart) Russell
For the true Annelides (Chaetopods) are too circumscribed and homogeneous a group to allow us to look to them for the ancestral forms of insects.
"Our Common Insects" by Alpheus Spring Packard
The vascular system is in the majority of Chaetopods a closed system.
"Encyclopaedia Britannica, 11th Edition, Volume 5, Slice 7" by Various
A similar constitution of the body is more clearly seen in the Chaetopod worms.
"Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 6" by Various