Harmothoe imbricata (Linnaeus, 1766)

Common name(s): Fifteen-scaled worm, Free-living scaleworm
Synonyms: Aphrodita imbricata Harmothoe imbricata
Phylum Annelida 
Subclass Palpata 
Order Aciculata 
Suborder Phyllodocida 
Harmothoe imbricata, about 3 cm long.  A few of the anterior elytra have fallen off this individual, revealing the segments underneath.  This individual was living within the tube of another polychaete in Fidalgo marina.
(Photo by:  Dave Cowles, July 2009)
Description:   As with other members of Family Polynoidae, the dorsal side of this species is covered with a series of platelike elytra. Harmothoe imbricata has 15 pairs of elytra which cover nearly all the segments (several elytra have fallen off the individual above).  The elytra have a light fringe of papillae around the edge (photo).  There is only one basic kind of notoseta and one kind of neuroseta on any given segment.  Most of the neurosetae fork at the tip (are bifid).  The notosetae are thicker than the neurosetae.  One pair of eyes is visible dorsally (unless covered by elytra), but the anterior pair of eyes cannot be seen except from the side (photo).  The lateral prostomial antennae are inserted ventrally to the medial antenna (photo).  Color highly variable, though brown is common.

How to Distinguish from Similar Species:  Several other species of Harmothoe have anterior eyes that are visible dorsally.  Other Polynoids may have other numbers of elytra.

Geographical Range:  A very widely distributed species. Found throughout the northern hemisphere.  Point Barrow, Alaska to s California on our coast.

Depth Range:  Low intertidal to 3710 m

Habitat:  Lives in a wide variety of habitats:  Freeliving intertidally under rocks and in eelgrass; subtidally in kelp holdfasts or mussel beds.  May live commensally with echinoderms or other polychaetes.

Biology/Natural History:   This scaleworm is very common in some parts of its range, such as California and SE Alaska.  It is an active swimmer and can live in a wide range of salinities.  The species is a predator which lies in wait, then pounces on its prey, using its large, jawed proboscis to subdue them.  Amphipods are common prey.  It also eats some algae.

The pink eggs are released from the nephridiopores.  In some areas, females of this species brood their eggs under the elytra; in other places they do not seem to do so.  Brooding in our area usually takes place in summer.  Larvae may have a long pelagic period or direct development.

Polychaetes this species may live commensally with include Thelepus crispus, Neoamphitrite robusta, and Diopatra ornata.


 
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References:

Dichotomous Keys:
  Carlton, 2007
  Kozloff, 1987, 1996

General References:
  Kozloff, 1993
  Lamb and Hanby, 2005
  O'Clair and O'Clair, 1998

Scientific Articles:

Web sites:

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

Head
This oblique view of the head shows the posterior eyes, which are visible dorsally, plus the anterior pair of eyes which are covered over by a flap of the prostomium.  The two lateral prostomial antennae are seen to be inserted ventral to the median antenna.  The anterior elytra were removed for this view.


Elytra
The elytra are fringed with fine papillae, especially along the posterior edges (to the right in this photo).
 
 


Authors and Editors of Page:
Dave Cowles (2009):  Created original page
CSS coding for page developed by Jonathan Cowles (2007)