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 A^. 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 in Long Island Sound 

 (Sanders, 1956), 300-600/m^ in Narragansett Bay (Davis, Phelps and Morrison, 

 unpublished), and up to 1500/m~ in Buzzards Bay (Sanders, 1960).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 (Harrington, 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 



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