being forced into consolidated sediment. This is accomplished by contracting 

 all body muscles, creating coelomic fluid pressure to expand anterior segments. 

 The hard, bullet-shaped muscular proboscis is forced into the sediment and the 

 pharynx finally everted when coelomic pressure reaches its peak. At this point 

 N. incisa inverts its pharynx, Uterally sweeping an emulsion of sediment into 

 the midgut, carried by fleshy, finger-Uke papillae at the tip of the everted 

 pharynx. Immediately the posterior region of the worm crawls into the new 

 cavity through peristaltic contractions. The bolting action is then repeated 

 until a new burrow to the surface is complete. Other means of polychaete 

 locomotion are also used by N. incisa for sediment penetration. Body 

 undulation common to nereids is typically used by A^. incisa to enter sediment 

 from the water column. This more rapid sediment penetration is used only 

 when A'', incisa lacks a sufficient anchor on the sediment. Peristaltic locomotion 

 in the Capitelhdae is limited to movement within a burrow cavity. Both 

 undulation and peristalsis involve a wave of segmental muscle contraction along 

 the body from head to tail if locomotion is directed forward (Schafer, 1962). 



Burrow maintenance by N. incisa appears limited to packing loose sediment 

 against the burrow wall as observed in Nereis spp. and is termed "wallpapering" 

 (Schafer, 1962). Burrow wall integrity may also be maintained by mucous 

 since it is readily observed covering the setae. In addition, Schafer suggested 

 that the iron oxides in the surrounding sediment (oxide halo) is itself a local 

 "cementing" of sediment. 



N. incisa develops temporary burrows, but unlike the continuous burrowers 

 (e.g. Paraonis, Heteromastis or Pectinaria), N. incisa rapidly completes a new 

 open burrow and then remains in it from one day during the summer to three 

 weeks in the winter. Such a burrowing sequence suggests that N. incisa is 

 abandoning discreet burrows rather than continuously meandering. The period 

 of temporary burrow residence, occupied with feeding and irrigation activities, 

 will be addressed in the following two papers (Davis, 1979 b,c). 



The magnitude and orientation of new burrow construction may offer 

 insight to in-sediment adaptations such as feeding or predator avoidance. InN. 

 incisa the scalar values of burrowing depth and breadth appear to be strictly 

 worm-size related, with larger worms burrowing increasingly deeper and 

 covering greater horizontal distances. The vector measurement of sequential 

 burrow direction appears to be random. This in contrast to other vagile 

 polychaete burrowers. Glycera and Nereis, for instance, develop burrow 

 galleries that maximize the worm's ability to exploit large areas of sediment 

 surface for prey and food debris respectively. The deposit-feeders Paraonis and 

 Heteromastis burrow in patterns termed "guided meandering". This systematic 

 exploitation presumably minimizes repeated ingestion of sediment recently 

 eaten. tV. incisa shows no indication of such adaptations. 



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