and/or from the collapse of old burrow walls. There is also avalanching of 
surface floe into efferent and afferent burrow openings. The volume of 
suspended sediment transported in this manner into the deeper benthos then is 
proportional to total burrow volume. 
Method of Burrow Building 
New burrow building is accomplished as TV. incisa first penetrates the wall of 
its existing burrow with an undulating proboscis, displacing small amounts of 
sediment. Worm position for this initial step is maintained through hydrostatic 
enlargement of the posterior segments. The worm next penetrates the sediment 
by lengthening the anterior segments and finally, as the head penetration 
reaches its forward limit, the pharynx everts, creating a bulbous cavity in the 
sediment. This type of sediment penetration has been described as “bolting” 
by Schafer (1962). He states that this is a common form of sediment 
penetration and is accomplished by contracting all body musculature. The 
resulting pressure forces coelomic fluid into the anterior region, forcing those 
segments without longitudinal muscles to expand and finally everting the 
pharynx at peak pressure. When the pharynx is re-inverted, TV. incisa swallows a 
slurry of sediment which was created as the compacted sediment was 
penetrated. The whole sequence is repeated until the worm occupies the new 
burrow fully and has established a new opening to the surface. The entire 
process can usually be accomplished in less than an hour. 
Spatial Extent of Burrowing 
A series of observations were made to determine if burrowing followed 
some functional pattern vs random burrowing and also to determine the 
horizontal and vertical scope of burrowing. A typical sequence of new burrow 
formation is illustrated in Figure 20-3. This figure is a two-dimensional 
reconstruction of a three-dimensional activity which is typically only partially 
visible against the glass wall. It represents an example of burrowing but does 
not indicate a predictable pattern of burrowing. Figure 20-3 shows actual 
tracings from weekly photographs of a different burrow building sequence (a 
single worm over a six-week period at 18°C). Observations were also made with 
worms in large dishes of sediment so that horizontal movement could also be 
assessed without wall interference. Each new afferent burrow opening was 
mapped, with new openings connected as a series of vectors (Figure 20-4). At 
the time of the last recording, the worm is probably lying in a burrow between 
opening 10 and 11, with the head located toward opening 11. The magnitude 
of ea<Ji horizontal vector was found often correlating with the size of the 
worm (Figure 20-5), with burrow length approximately 2-3 times the length of 
TV. incisa. Yet exceptions do occur, as shown in Figure 20-4 by the short 
distance to afferent openings 2 and 4. By observing 30 six-week sequences of 
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