Arctonoe pulchra (Johnson, 1897)

Common name(s): Red commensal scaleworm

Synonyms:  Polynoe pulchra, Acholoe sp., Halosydna sp.
Phylum Annelida
 Class Polychaeta
  Order Phyllodocida
   Superfamily Aphroditidae
    Family Polynoidae
Arctonoe pulchra, about 2 cm long.  Was living on the sea cucumber Parastichopus californicus caught near Rosario. 
(Photo by: Dave Cowles, July 2006)
Description:  As with all Polynoids, this species is mostly benthic, few if any of the segments are longer than wide when contracted, the dorsal surface has clearly visible elytra, and all of the neurosetae are simple.  Arctonoe pulchra has at least 20 pairs of elytra, elytra are on segments 2, 4, 5, then every other segment to 23, 26, 29, then every other segment to the end of the body.  The edges of the elytra are smooth (photo), and they nearly meet along the animal's dorsal midline.  It has no prominent nuchal fold and the lateral prostomial antennae are inserted slightly ventral to the edge of the prostomium, may have few or sometimes no notosetae.  The neurosetae are falcate, with pointed tips, and hooked.  Most individuals are brick red, and the species has no dark band across segments 7 and 8.  Up to 7 cm long.

How to Distinguish from Similar Species:Arctonoe vittata has a band of dark pigment extending across segments 7 and 8.  Arctonoe fragilis has ruffled or folded margins on the elytra.

Geographical Range:  Gulf of Alaska to Baja California, Mexico; uncommon in California

Depth Range:  Lower intertidal to 275 m

Habitat:  Symbiotic with several invertebrates including sea stars such as Solaster stimpsoni, Pteraster tesselatus, Luidia foliata, and Dermasterias imbricata, sea cucumbers such as Parastichopus californicus and P. parvimensis, and other animals such as  Cryptochiton stelleri, Diodora aspera, Megathura crenulata and terebellid polychaetes such as Loimia montagui.

Biology/Natural History:  This species is attracted by the smell of its host (if the host is uninjured), but can learn to live with a new species.  Its body color is usually close to that of its host.  It eats detritus.  Adults are territorial and will try to drive other individuals off their host.  They may injure or kill one another in fights over a host.

Members of Family Polynoidae, unlike most other errant polychaetes, have parapodia specialized for walking rather than as paddles.  Their longitudinal muscles, which caused lateral undulations in other polychaetes, are poorly developed and they don't undulate much.  As a result, although they can walk efficiently they are poor swimmers.

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Dichotomous Keys:
  Kozloff 1987, 1996
  Smith and Carlton, 1975

General References:
  O'Clair and O'Clair, 1998
  Ricketts et al., 1985
  Sept, 1999

Scientific Articles:

Web sites:

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

The edges of the elytra on this species are smooth, as seen in this closeup photo.  This individual also has a red spot on each elytrum. Ricketts et al. says all members of the species have this spot (but that A. vittata do not), while O'Clair and O'Clair say that some individuals may not have the spot.

Authors and Editors of Page:
Dave Cowles (2006):  Created original page