Home > Northwest Shells & Marine Life > PNW Shells & Marine Life Photos > Bivalves >  Bivalves - Pholadidae


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Click on photo to enlarge.  Scale line in photo equals 1cm unless otherwise specified.
* Species which are commonly encountered on the beach.









Bivalves 

Family Pholadidae







   












 


















Penitella conradi
Bamfield, BC
































Zirfaea pilsbryi Zirfaea pilsbryi Zirfaea pilsbryi
      Petersburg, AK                               Pender Island, BC, intertidal                                Pender Island, BC, very shallow water at low tide


Penitella conradi Valenciennes, 1846
Abalone Piddock
intertidal to 20m          size to 35mm
northern Mexico to northern BC
This shell is infrequently found.  It bores into Abalone shells and sometimes a few other thick-shelled species.  This does not kill the abalone.




Penitella penita
Campbell River, BC, found at very low tide in mudstone

Xylophaga washingtona
off Point Chehalis, WA
Xylophaga washingtona Bartsch, 1921
Washington Woodeater
subtidal, 75 to 2300m          size to 6mm
southern California to northern Alaska
This is rarely found intertidally, usually only when its habitat of waterlogged wood and plant debris is washed ashore.  Its small size makes it difficult to see.







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Penitella penita Penitella penita
         both - Whiskey Creek Beach, WA




Penitella turnerae
Penitella turnerae
both - Pender Island, BC, intertidal

 
This page last revised: 6-25-2019

Penitella penita (Conrad, 1837)
Flat-Tip Piddock *
intertidal to 90m          size to 95mm
northern Mexico to northern Alaska
This is commonly found intertidally.  It bores into clay, shale, sandstone and even concrete.  The shell narrows at the posterior end and there is a flaring, almost rubbery tip extending from the periostracum, the siphonoplax.  It is the only one of our local species which exhibits this.  The siphon is smooth.  The shell is fragile and often breaks apart where the sculpture changes pattern.






Penitella turnerae Evans & Fisher, 1966
Turner Piddock
intertidal to 5m          size to 120mm
central California to northern BC
This species is somewhat common intertidally, but is hard to find because the shell bores into soft rock and hard clay.  It is most often confused with P. penita.  This shell does not have a siphonoplax.  The siphon is smooth.  




Penitella richardsoni Penitella richardsoni
   Pender Island, BC, intertidal                                        Rich Passage, WA, intertidal
Penitella richardsoni Kennedy, 1989
Monterey Piddock
intertidal to 5m          northern Mexico to southern BC          size to 60mm
This is somewhat common intertidally, but is hard to find because the shell bores into soft rock.  The siphon exhibits pustules which are dense in the center of the siphon and become sparse near the tip.  The shell is very similar to our other piddocks although this shell tapers more toward the siphon end.
(synonym - Penitella gabbii)

















Zirfaea pilsbryi Zirfaea pilsbryi Zirfaea pilsbryi
                 interior of inhalent siphon                  "twinned" exhalant siphon, photographed subtidally   an extra exhalant siphon, subtidal
                     Rich Passage, WA                                                                           both twins - Rich Passage, WA                         
Zirfaea pilsbryi Lowe, 1931
Rough Piddock *
intertidal to 125m          northern Mexico to northern Alaska          size to 150mm
This is more often found by sighting the siphons than finding the shells.  The siphons have a unique, irregularly-ridged siphon and finger-like projections at the lip of the siphon opening.  The clams burrow into mud or clay as deep as two feet.  The siphon can stretch quite far, much like a geoduck.  Occasionally some unusual three-holed siphons have been sighted.  The "twinned" siphon can be either the inhalant or exhalant siphon.  One was even found with both siphons twinned!