Rapid Crawling and Swimming
Rapid Crawling
This movement depends upon mainly on the contralateral waves of contraction of the longitudinal muscles of the body wall that causing lateral undulations of the body. The parapodial activity explained above supplements the body undulations. This results in rapid crawling. The crawlers involves polychaetes of many families such as nereids, syllids, phyllodocidae etc.
Swimming
The movements included are basically similar to rapid crawling mentioned above but during swimming the waves are fewer but larger and much more frequent. The animals are pelagic, having no contact along with the substratum. Many crawlers as well swim, but some like alciopids and tomopterids are exclusively pelagic.