Penitella turnerae Evans and Fisher, 1966

Common name(s): Piddock clam

Synonyms: x
Phylum Mollusca
 Class Bivalvia
  Subclass Heterodonta
   Order Myoida
    Suborder Pholadina
     Family Pholadidae
Penitella turnerae found in shale near Lincoln City, OR by Bob Mead.  Longest shell is 5.5 cm long and 2.6 cm wide.  Right valve is above, left valve is below.  Anterior end is to the right.
(Photo by: Dave Cowles, May 2006)
Description:  Family Pholadidae are the piddock clams, which bore into shale, clay, or firm mud.  Much of the anterior portion of the shell is roughened so that the animal can rasp a hole in the rock or clay much like an augur bit (photo).  The anterior portion of the shell, while higher and more globose than the posterior portion, is not nearly globular.  In this species, the anterior portion occupies less than half the length of the valve and is separated from the posterior in a well-defined manner by a groove which runs from the dorsal to the ventral side.  It has a myophore (apophysis) in both valves (photo).  The posterior end of the shell, though narrower than the anterior, does not taper to a point like a bird's beak.  In small individuals there is a gape between the valves at the anterior end for the foot to protrude, but in a full-grown specimen such as the individual above the gape has been covered over by a calcareous callum (photo).  It has no calcified siphonoplax.  The anterior end has a thick, shieldlike extension of the callum dorsal to the anterior rasping portion (photo).  The umbonal reflections (the calcified plates between the dorsal callum extension and the rasping portion of each valve) are tightly applied to the shell (as opposed to being free from the shell for part of their length, especially at the anterior end) (photo).

Note:  I found no evidence of a siphonoplax on this individual.  If it did indeed have a siphonoplax it would key to Penitella penita, a more commonly encountered species.

How to Distinguish from Similar Species:Penitella richardsoni has umbonal reflections free from the anterior rasping part of the shell for about half the length of the reflection. Penitella conradi and Penitella penita have a siphonoplax. Zirfaea pilsbryi has an anterior rasping portion about half the length of the valve, plus its anterior gape does not close. Netastoma rostrata has no myophores.  The anterior portion of Barnea subtruncata is not clearly set off from the posterior portion by a groove.  Parapholas californica lives farther south, its valves are clearly divided into three sections, and it has distinctive overlapping plates of periostracum on the posterior end.

Geographical Range:

Depth Range:


Biology/Natural History:

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Dichotomous Keys:
  Kozloff 1987, 1996

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

An inside view of the same individual as above.  The upper (left) valve has been broken off somewhat at the posterior end.

x labeled
In this closeup view of the hinge of the right valve, the dorsal extension of the callum, hinge, inside of the umbonal reflection, and the myophore can be clearly seen.


x x
In this view of the anterior end, the dorsal side with the dorsal extension of the callum can be seen on the left.  The ventral side, which in smaller individuals gaped so that the foot could be protruded but now in this mature individual has been sealed by a calcareous
callum, can be seen to the right.


External parts labeled

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