Abarenicola pacifica

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.

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.

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

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.

Depth range based on 4 specimens in 1 taxon.

Environmental ranges
  Depth range (m): 0 - 1.9

Graphical representation

Depth range (m): 0 - 1.9
 
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Depth Range: Intertidal and subtidal; mostly intertidal.

Habitat: Muddy sand of quiet, non-exposed bays