semipermanent vertical burrows to reach deeper sediment in which it 
continually burrows and deposit-feeds. Oxygen exchange occurs near the 
sediment-water interface using modified posterior segments when the worm 
surfaces to defecate (Linke, 1939 ).Paraonis spp. continually burrow to form a 
deposit-feeding ring within a single stratum of high organic content (Gripp, 
1927, cited in Schafer, 1962). When the concentric burrowing reaches 8-10 cm 
in diameter, the worm burrows to a new stratum to begin another feeding ring. 
Partially or non-vagile families such as the Arenicolidae and Chaetopteridae 
possess U-shaped burrows and irrigate for the dual purposes of feeding and 
respiratory exchange. Families with the least sediment contact, termed 
tubicolous polychaetes, include the Sabellidae, Onuphidae and Serpulidae. 
These worms develop permanent tubes lined with mucopolysaccharides, shell 
debris, sand grains or calcite. They generally feed and ventilate above the 
sediment-water interface. There are many exceptions; for instance, the 
tubicolous Pectinariidae drag their sand grain tube horizontally through the 
sediment using it as an irrigation tube to the surface as they deposit-feed 
below. 
The present investigation provides information on the microhabitat of N. 
incisa by describing the nature of its burrow and examining some of the 
variables influencing burrowing. Employing laboratory in situ microcosms, 
coupled with direct observation in the field for verification, this investigation 
has addressed such topics as the form and make-up of the N. incisa burrow, 
how it is constructed, what is its horizontal and vertical extent, and how the 
rate of burrowing is influenced seasonally as the worm is exposed to 
temperatures which can range from 0-24°C. 
MATERIALS AND METHODS 
Nephtys incisa used in this study were collected from a station north of 
Conanicut Island, Narragansett Bay, Rhode Island (Figure 20-1). This benthic 
station is characteristic of a large portion of the Narragansett Bay, where a 
clayey-silt sediment covers 60-75 percent of the Bay bottom (McMasters, 
1960). Previous studies (Davis, et al ., unpublished) found N. incisa density to 
drop off rapidly in the sandy sediment toward the Bay mouth and decrease 
gradually toward the northern head of the estuary, the latter possibly due to a 
pollution gradient (Farrington, et al., 1973). 
N. incisa were collected by gently sieving Smith-Mclntire grab samples and 
by SCUBA diver-collected box cores, which were then transported intact to the 
laboratory and held in flowing seawater. When temperature change was 
required, it was shifted at a rate of 2°C per week, which is comparable to the 
rate of temperature change in the field (Figure 20-2). 
304 
