Panopea abrupta (Conrad, 1849) Common name(s): Pacific geoduck clam, Geoduck clam (pronounced "goo'-ee-duck"), King clam
Synonyms:  Panopa abrupta, Panope generosa, Panopea generosa
Phylum Mollusca Class Bivalvia Order Myoida  Suborder Myidae  Family Hiatellidae
	This shell, 19 cm long, was collected in the 1800's.  It was held until recently in the Washington State University museum.
	(Photo by: Dave Cowles )

Description:   This gigantic clam has fused siphons far too large to fit into the mantle cavity (photo).  The siphons can project up to a meter from the shell and cannot be retracted into the shell.  The shell is dirty white to cream with a small amount of yellow periostracum (photo).  It has well-developed concentric growth lines but no radial ribs.  Each valve has one hinge tooth.  The shell gapes widely on all sides except the hinge, and very widely on the posterior (siphon) end (photo  photo).  Unlike most members of its family, its pallial line is continuous and wide (photo).  The long siphons ares light brown with darker brown on the end (photo).  There are no thick pads on the end of the siphons.  Shell is quadrate (approximately rectangular in outline), more rounded on the anterior than the posterior end, up to 23 cm long, animal to 9 kg.  The single hinge teeth of the two valves do not match well.

How to Distinguish from Similar Species:  This is our largest local clam.  Other members of family Hiatellidae are smaller and have gaping valves but a discontinuous pallial line.  Gaper clams such as Tresus capax do not get as large and gape mainly at the posterior end.  The Atlantic geoduck, P. bitruncata, does not live here and is smaller.

Geographical Range: Coast of Asia down to Japan; in North America from central Alaska to Newport Bay, CA; Mexico; Panama.  In the Salish Sea area they are especially common in Hood Canal and Puget Sound.  More common here than farther south.

Depth Range: Subtidal down to 100 m depth

Habitat:  Burrows very deeply (to 1.3 m) in soft bottoms in quiet waters.

Biology/Natural History:  This animal is said to be the largest burrowing clam.  It does not mature until age 3-4. Spawning is in the spring.  Young clams have spiny shells and often settle on the tubes of polychaetes, where they attach for a time by byssal threads before dropping off and digging into the sediment.  It is very long-lived (up to at least 168 years).  The copepod Herrmanella panopeae (Cyclopoida: Lichomologidae) has sometimes been found as a symbiont inside the shell.  Adults of this species are poor diggers and do not seem to be able to dig themselves back into the mud if removed.  Ricketts et al. state that the shell is lightweight but the shell of the specimen above is probably 1/2 cm thick.

References:

General References:
  Abbott, 1986
  Harbo, 1997, 2011
  Johnson and Snook, 1955
  Kozloff, 1993 (as P. generosa)
  Lamb and Hanby, 2005
  Morris, 1966 (as P. generosa)
  Niesen 1994, 1997 (as P. generosa)
  O'Clair and O'Clair, 1998
  Rice, 1971
  Ricketts et al., 1985
  Sept, 1999
  White, 1976

Scientific Articles:

Web sites:

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

  I have never found this clam in the region right near Rosario Beach Marine Lab, except on commercial farms such as Taylor Shellfish Farm.  It is much more common in the southern reaches of the Salish Sea such as Puget Sound and Hood Canal.  It is also found in British Columbia.

The shell gapes widely, especially on the posterior (siphon) end (to the right)

The shell has a very well-developed pallial line and one hinge tooth in each valve.  The shell of this specimen is about 1/2 cm thick.  Along the edges the shell splits into an inner and an outer shelf which diverge from each other slightly.  I have not seen this divergence into shelves described for this species.
 

This view of a living individual from the right side illustrates the fact that the siphon is so large that it cannot be retracted into the shell and the shell therefore gapes widely. Photo by Dave Cowles, August 2016 of a farmed clam at Taylor Shellfish Farms near Rosario.

The same individual from the ventral side

The same individual from the dorsal side.

These are the siphons of a geoduck clam feeding at 50 foot depth in Burrows Bay. The siphons can be very large (up to 5-7 cm in diameter each). They are smooth and white inside, united all the way to the top, and have a smooth opening with no screening tentacles, but the outside is brown and rough. Photo by Dave Cowles, August 2019

Rosario Invertebrates web site provided courtesy of Walla Walla University