Abarenicola pacifica or the Pacific lugworm is a large species of polychaete worm found on the west coast of North America and also in Japan.

Abarenicola pacifica is a large worm growing up to fifteen centimetres in length with an elongated, segmented body which is tapered at both ends.

There are some capillary setae and the segments in the middle region bear up to thirteen trunk-like sets of gills which are red due to the hemoglobin circulating in the blood.

[2][3] A. pacifica is found in the intertidal and subtidal zones round the coasts of North America between Alaska and northern California and in Japanese waters.

[2] It is found living under the surface of sand flats and muddy shores, and in estuaries where it can tolerate salinities of as low as 23% of normal seawater for short periods, although 50% is a more sustainable level.

[5] At low tide, when the sediment in which the lugworm is living is no longer covered by water, aerial respiration takes place.

The worm helps transport sediment from lower depths to the surface where aerobic microbes can break down the pollutant hydrocarbons.

[12] It is considered to be useful as an indicator species for monitoring ecological conditions after an oil spillage, being the second most useful organism after the Baltic clam (Macoma balthica).

Disturbance to the sediment has also been associated with a decline in the abundance of the polychaete Pygospio elegans and the crustacean Cumella vulgaris, both of which happen to be predators on juvenile lugworms.