Clams in Order Nuculida
to one another. The hinge
plate has taxodont
dentition. The shell is aragonitic, longer
and has no radial
ribs. The periostracum
is smooth. They are protobranchs, so their gills are simple
leaflets suspended in the mantle cavity. They have large palps
near the mouth which they use to gather food. Members of
have an external hinge
ligament, the interior of the valves
is not pearly, they have siphons
and a pallial
sinus, they have a chondrophore,
and the shell gapes at theposterior
end (to the right in the photo above). Yoldia
a flattened (not swollen) shell, the posterior
end is rather pointed rather than truncate.
It differs from other members of the family in that the valves
have fine concentric sculpturing which does not coincide with the
growth lines, but instead crosses over them (photo).
and central. The dorsal
margin of the shell anterior
to the umbo is slightly convex. Shell is white with a smooth,
yellow or greenish tan periostracum.
Rarely over 4 cm long.
Yoldia seminuda (Dall, 1897)
Common name(s): Crisscross Yoldia
|Yoldia seminuda trawled from 15-18 m
depth off Canoe Island,
San Juan Island, WA.
Captured July 1987 and preserved before photographing. The
can be seen extending from the anterior end of the shell.
|(Photo by: Dave Cowles
How to Distinguish from
Other Yoldia species do not have the concentric
lines on the shell
which cross the growth lines. Macoma yoldiformis
is a Macoma
clam which also is white with a smooth, shiny periostracum
but, among many other differences, does not have taxodont
Arctic ocean to
San Diego, CA
Subtidal, 15-150 m.
In fine sand and mud
lives in the sediment and eats detritus which is picked up by extending
the long palps into the sediment and moving detritus toward the mouth
ciliary action. Unlike other groups of clams, the gills are
for respiration only--not for feeding.
Yoldia is a protobranch bivalve, meaning its gills are bipectinate
and it does not feed using its gills (see above). It is also
because its shell valves are equal and have taxodont
and Blake, 1998
1966 (as Y. scissurata)
General Notes and
Observations: Locations, abundances,
Strong side light (here from above, from the dorsal side) shows the
fine concentric striations on the shell that cut across the concentric
growth lines. The growth lines are centered on the umbo,
other striations are centered to the right (posterior to) the
The foot can be seen protruding from the anterior end of the shell to
Authors and Editors of Page:
Dave Cowles (2006): Created original page