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
portion comprises about half the shell (photo)and
is separated from the posterior nonrasping portion by a oblique groove
There is no protoplax
but there is a mesoplax.
shell tapers a bit but not to such an extent that it resembles a bird's
The white valves
gape at the posterior
end for the thick, united siphons.
be withdrawn into the shell. The valves
have coarse concentric ridges; on the anterior end these ridges often
filelike projecting spines or teeth which are used for
end of the valves
also often has projecting spines or teeth on the valve
margin (photo), and
also has a gape through
which the foot protrudes (photo).
gape is not closed by a callum
even in older individuals. the periostracum
is brown and may be seen extending onto the base of the siphons.
small chitinous spots on the surface. The interior of the valves
is chalky with well-defined muscle
scars. Length up to 15 cm. This
is one of our largest
Zirfaea pilsbryi Lowe, 1931
Common name(s): Rough piddock,
Pilsbry piddock, Pacific rough
Zirphaea gabbi, Zirphaea
|Zirfaea pilsbryi found burrowing in
hard mud in Fidalgo Harbor
under the railroad trestle.. Total length 7 cm, shell length
The anterior of the shell and the white protruding foot are on the
The siphons are on the right.
|(Photo by: Dave Cowles,
How to Distinguish from
Similar Species: Barnea
subtruncata does not have the anterior
portions of the valves
separated by a groove. Netastoma rostrata
has a calcified
and lacks myophores,
plus the posterior
end of the shell tapers to a point like a bird's beak. The Penitella
species such as P.
have the anterior
rasping portion comprising less than half the length of the valve, have
and the anterior
gape becomes sealed with a callum
in mature individuals. These other species also do not have
(spines) along the edge of the shell and most of them can withdraw
into the shell.
Chukchi Sea, Siberia
to Baja California, Mexico
Low intertidal to 126
m; mostly below -1.0 feet tide level.
Common in hard mud or clay,
shale, or sandstone; in bays and estuaries; occasionally along the open
coast. Occasionally bores into wood buried in the mud.
piddock clams, this species can live outside its burrow for long
of time (months). Can burrow to 50 cm depth.
in clay which is covered by a layer of sand, in which case it must
way. It can extend its siphons
up through as much as 48 cm of clay plus 30 cm of sand. When
it holds onto the substrate with its foot and rocks its shell up and
against the burrow walls by alternately contracting its anterior and
adductor muscles. After each stroke the animal rotates about
It takes about 30 rocking motions to turn in a complete circle, which
about 70 minutes. After about one complete turn, the
rotation is reversed. Periodic body contractions create a
which shoots debris up and out the incurrent
siphon. Lives about 8 years, and never completely
and Fairbanks, 1966
and Carlton, 1975
and Snook, 1955 (As Zirphaea gabbi)
and McConnaughey, 1985
et al., 1980
and O'Clair, 1998
et al., 1985
General Notes and
Observations: Locations, abundances,
A closer view of the animal in its shell. Anterior is to the
right. Note the rasping anterior portion of the shell, which
about 1/2 the shell length, and the white foot which protrudes both
Authors and Editors of Page:
Dave Cowles (2006): Created original page