Abarenicola pacifica Healy and Wells, 1959 Common name(s): Pacific lugworm, Pacific neapolitan lugworm
Synonyms:
Phylum Annelida  Class Polychaeta Order Capitellida  Family Arenicolidae
	Abarenicola pacifica, found on March Point, Padilla Bay, June 2009.  View is of the dorsal and right sides.  Anterior end is to the right.  The red, bushy structures are gills filled with blood which has red hemoglobin.  In closeup one can see that the gills are continually flexed and turned, providing water flow over them.
	(Photo by:  Dave Cowles)

How to Distinguish from Similar Species:Arenicola marina has the neuropodia of its posterior gill-bearing segments nearly meeting at the midventral line. Abarenicola claparedi has the ventral side of its nephridiopores covered with a flap of skin and it lives in areas with more wave action.  Many lugworms (family Arenicolidae) can be fully reliably distinguished only by internal anatomy.

Geographical Range: Japan, Pacific coast from Alaska south to Humboldt Bay in northern California

Depth Range:  Intertidal and subtidal; mostly intertidal.

Habitat:  Muddy sand of quiet, non-exposed bays

Biology/Natural History:   Lives in an L-shaped burrow, head down.  It everts its esophagus then pulls it in, thus ingesting mud and feeding on organisms such as nematodes within it.  Periodically it backs up to near the surface to defecate, forming the characteristic mound around its burrow.  The mound will often have coils of castings roughly 1/2 cm in diameter.  The lugworm pulses its body while within the burrow to bring in oxygenated water.

References:

General References:
  Kozloff, 1993
  Lamb and Hanby, 2005
  Niesen, 1994
  Niesen, 1997
  Ricketts et al., 1985
  Sept, 1999

Scientific Articles:

Web sites:

General Notes and Observations:  Locations, abundances, unusual behaviors:


This ventral view of the head shows that it has no obvious external head appendages

This view, taken a few seconds after the one above, shows the large esophagus which is everted during feeding.  The esophagus expands outward like the head of a mushroom.

The anterior third of the body, anterior to the gills,  has relatively long segments and the notopodia and neuropodia are well separated.  In this view the head is to the right and dorsal is up.  The first gill-bearing segment is on the left.  The capillarynotosetae-bearing notopodium can be seen near the top of the segment in the center, while the uncini-bearing neuropodium can be seen well below the notopodium next to the piece of debris.

The gills are notopodial (dorsal) and filled with hemoglobin-containing blood.  The animal writhes and waves them gently, likely increasing water circulation over them.  Note the long capillary setae on the notopodia (top) and the uncini on the neuropodia (lower).

The posterior segments have no setae, so that the back third of the body appears almost like a "tail".  Note the last gill and setae-bearing segments at the right of the photo.

This is a view of the last segments and the pygidium (posteriormost segment)
 

This ventral view of the posteriormost gill-bearing segments shows that the neuropodia of these segments do not nearly meet at the midline.

The worm creates burrows with large mounds at the entrance such as this one.  Often fecal castings can be seen on top of the mound.