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, literally sweeping an emulsion of sediment into 
the midgut, carried by fleshy, finger-like 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 N. incisa to enter sediment 
from the water column. This more rapid sediment penetration is used only 
when N. incisa lacks a sufficient anchor on the sediment. Peristaltic locomotion 
in the Capitellidae 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. In N. 
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. N. incisa shows no indication of such adaptations. 
315 
