Soft-bodied organisms that burrow into the sediment generally do so for 
predator avoidance, at the minimum. Those which burrow continuously 
through the sediment, such as the Nephteidae, Nuclionid bivalves and 
Haustorid amphipods, do so- to obtain food either as predators or 
deposit-feeders. This vagile or wandering mode of life requires adaptations, not 
only for burrowing, but also for obtaining sufficient food and dissolved oxygen 
in this environment. The specific questions that have been investigated concern 
adaptations for burrowing, feeding and irrigation in N. incisa. The present 
paper will address certain questions of burrowing activities, while the two 
subsequent papers (Davis, 1979 b,c) will deal with feeding and irrigation 
activities in N. incisa. These activities are interrelated in that continuous 
sediment burrowing is generally a feeding adaptation and necessitates further 
adaptation to obtain well-aerated seawater while moving through the sediment. 
N. incisa occurs in estuarine, shallow coastal waters and across the Atlantic 
continental shelf from Chesapeake Bay northward to Nova Scotia, Greenland 
and Iceland, and along the European coast from the North Sea, the Baltic Sea, 
and south into the Mediterranean (Pettibone, 1963; Thorson, 1946; Bellan, 
1969). Reported population densities include 600/m 2 in Long Island Sound 
(Sanders, 1956), 300-600/m 2 in Narragansett Bay (Davis, Phelps and Morrison, 
unpublished), and up to 1500/m 2 in Buzzards Bay (Sanders, 1960). Population 
age structure has been examined temporally by Sanders (personal 
communication) who has observed three and sometimes four year classes, with 
each new year class appearing as 2 mm worms during early spring. Density of 
N. incisa can be correlated with sediment clay-silt content (Sanders, 1956), 
pollution gradients (Farrington, Quinn and Davis, 1973), and possibly 
meiofauna density (Tenore et al , 1977). 
The types of burrows found among infaunal polychaetes range from totally 
permanent to highly temporary. In the case of completely vagile worms such as 
the Nephteidae, Nereidae and Glyceridae, this in-sediment wandering may lead 
to burrow galleries and multiple openings to the surface. This mode of 
burrowing is generally adapted to exploit debris or prey on the sediment 
surface while minimizing exposure to predators. Two or more openings to the 
water also permit efficient one-way irrigation to obtain dissolved oxygen. 
Glycera alba produces such a gallery, using various burrow openings as prey 
vibration conduits and will even intercept moving prey at other gallery 
openings (Ockelman and Vahl, 1970). Nereis diversicolor has a similar gallery 
to better exploit debris on the sediment surface. An interesting adaptation for 
secondary filter feeding in this species was described by Harley (1950). Under 
certain conditions the respiratory irrigation stream is directed into a mucous 
funnel which is then eaten. Other vagile polychaetes burrow to exploit 
subsurface organic-containing sediments, for example the Capitellidae, 
Maldanidae and Paraonidae. The capitellid Heteromastus filiformis develops 
303 
