Fifteen-scaled Worm    Harmothoe imbricata


This odd looking creature is one of the many polychaete worms found in the Pacific Northwest.  Polychaete worms are segmented worms and are members of the Annelid phylum.  However unlike its polychaete kin, this species, along with its close relatives, uses large scales (or elytra) to protect it's flattened body from attack.  The attachment of the scales are rather loose so some have been lost from this specimen during handling.  There are around six local fifteen-scaled species with the most common being H. imbricata.  In addition there are about 16 other kinds of scaleworms that inhabit the northeastern Pacific Ocean - many of which are commensals on sea stars, sponges, limpets, chitons and sea cucumbers.  Most species are small, only an inch or so in length: H. imbricata grows up to 2.6 inches.  The female broods the larvae under her scales till they swim away to settle on the bottom.


H. imbricata is mainly free living and can be found hiding or slowly crawling around sponges and hydroids under floats or under rocks, around eelgrass and in kelp holdfasts.  It also can be found as a commensal in the tubes of several other kinds of polychaete worms.  They feed on living organisms which they detect with their anterior sensory structures and then catch with their jawed protrusible gullet.  When living in close association with another organism they usually feed on leftovers from the host species.  H. imbricata is circumpolar in both the Pacific and Atlantic Oceans.  Other species occur from Alaska to California.