commonly observed in the field. Experimental worm density was one per 
experimental aquarium or one worm/28 cm^. The aquaria were kept in the 
dark except for a two-minute interval once weekly when both sides of the 
squaria were photographed. 
Patterns and rates of burrowing and sediment aeration were described from 
sequential photographs of the worm burrows constructed against the glass wall 
of the sediment-filled thin aquarium. Sediment aeration by local burrowing and 
irrigation was indicated by a change in sediment color from dark to light and 
provided a record of the worm’s present or past location. This method relies on 
oxygen-sediment-color relationships proposed by Fenchel and Riedl (1970), 
Hayes (1964), Teal and Kanwisher (1961), Rhoads, Aller and Goldhaber 
(1977), and Aller and Yingst (1978). The absence of oxygen generally leads to 
a dominance of reduction reactions (eH<0) including formation of iron 
sulfides which blacken the sediment. At the point of change from dark to light 
color in the sediment, values for both eH (volts) and dissolved oxygen (mg/1) 
begin to increase from 0.0. Presence of oxygen is key to substrate oxidation 
reactions (eH<0). By quantifying the development of this color discontinuity 
against the thin aquarium glass wall where worms are burrowing, it is possible 
to document three parameters of burrowing activity: 1) the spatial-temporal 
extent of burrowing, 2) the effective new surface area of the sediment-water 
interface, and 3) the extent of sediment aeration. This record, visible against 
the aquarium wall, can be photographed at appropriate time intervals and 
activity quantified by counting burrows, measuring the surface area of burrow 
linings and by planimetry, measuring the volume of aerated sediment. 
Horizontal burrowing patterns were also described by recording temporal and 
spatial appearance of new burrow openings at the sediment surface in large 
sediment-filled dishes (single .2-.3 g worms in 3 x 6 x 4” deep sediment trays). 
RESULTS 
Description of the Burrow 
Nephtys incisa actively penetrates fine sediments and establishes an 
open-ended burrow with no visible modification of the burrow wall except 
packing. It is not known if mucous, exuded onto parapodial setae during 
feeding (Davis, 1979b), is present in the burrow wall. The burrow is often 
W-shaped, but many variations exist. Back and forth motion of the worm with 
packing of the burrow wall by setal bundles creates a section which is closely 
fitted to the front and mid section of the worm. This precise fit permits 
flow-through irrigation by the parapodial cilia (Davis, 1979c). The occupied 
burrow is often continuous with a recently abandoned burrow posteriorly, 
which then continues to receive oxygenated water before it returns to the 
surface. Abandoned burrow segments gradually till with suspended particulates 
307 
