Dear Larry,
I have seen several species of pectinarrids, collected near California from the depth more than 1 km, they have single layer tubes as well. However it does not mean that there are no tubes with more than one layer
wormly Igor
--
Dr. Sc. Igor A. Jirkov
Leading Scientific Researcher
Department of Hydrobiology
Biological faculty
Moscow State University
Moscow
Russia
http://hydro.bio.msu.ru/Personal/Jirkov.htm
