Pholadidae are the
piddock clams, which bore into shale, clay, or firm mud. Much
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).
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
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
has no calcified siphonoplax.
end has a thick, shieldlike extension of the callum dorsal to the
anterior rasping portion (photo).
(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,
at the anterior end) (photo).
Penitella turnerae Evans and Fisher,
Common name(s): Piddock clam
|Penitella turnerae found in shale
near Lincoln City, OR by Bob
Mead. Longest shell is 5.5 cm long and 2.6 cm wide.
is above, left valve is below. Anterior end is to the right.
|(Photo by: Dave Cowles,
Note: I found no evidence of a siphonoplax
on this individual. If it did indeed have a siphonoplax
it would key to Penitella
a more commonly encountered species.
How to Distinguish from
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.
has an anterior
rasping portion about half the length of the valve,
plus its anterior
gape does not close. Netastoma rostrata has no myophores.
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
plates of periostracum
on the posterior end.
General Notes and
Observations: Locations, abundances,
An inside view of the same individual as above. The upper
valve has been broken off somewhat at the posterior end.
|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.
|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
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