Peristaltic waves of tubicolous worms and the problem of irrigation in Sabella pavonina

A simple scheme is presented to illustrate four possible kinds of locomotory peristalsis in worm-like animals. The application of this scheme to real animals is discussed. Peristaltic waves may be of constriction or dilatation. A continuous body cavity enables the worm to regulate both speed and direction of travel by controlling the relative tonus of its body wall muscles. Thus peristaltic waves can be used to pump water without causing locomotion.
Sabella irrigates its tube by peristaltic swellings but the coelom and intestine are sub-divided by entire septa. Anatomical and morphological features which allow the shortest, widest segments forming a "piston" to slide down the tube and the narrower elongated segments to grip its walls are considered. In this way the construction of the typical body segment is given a functional explanation.
The functions of septa in annelids are discussed.