Abarenicola pacifica Healy and Wells, 1959

Common name(s): Pacific lugworm, Pacific neapolitan lugworm

Synonyms:  Abarenicola pacifica
Phylum Annelida 
Order Capitellida 
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)
Description:   As a member of family Arenicolidae, this species is large and wormlike, without bulbous eyes, has few if any external head appendages but does have a prostomium.  It can evert its esophagus during feeding, which appears as a wide mushroom-cap-like structure (photo).  Most segments are not longer than wide.  Many of the parapodia have setae but the body is not covered with special paleae, felt, or elytra. The capillary setae (eg notosetae) are not cross-barred.  Segments in the middle third of the animal have gills (see above photo).  Features distinguishing this species include the fact that it is a large worm (over 2.5 cm as an adult) which does not secrete a tube, the posterior third of its body has no setae (photo), its gills are bushy (photo), it has 4-7 pairs of esophageal caeca, the first of which is the longest, the neuropodia of its posterior gill-bearing segments do not nearly meet at the midventral line (photo), and its nephridiopores are completely exposed.  Thirteen or less gills.  Length to 15 cm.  The anterior, middle, and posterior body portions often are colored slightly differently leading to the "neapolitan" designation.

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.



Dichotomous Keys:
  Carlton, 2007
  Kozloff, 1987, 1996

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

Head with everted esophagus
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.

Anterior body
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.

Gill-bearing central segments
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).

Posterior segments
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)

Ventral side below posterior gills
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.

Authors and Editors of Page:
Dave Cowles (2008):  Created original page
CSS coding for page developed by Jonathan Cowles (2007)