>I have often found "stained shells" (from anoxic sediments) but was
>recently sent a specimen of the green false-jingle, or jingle
>shell, Pododesmus macrochisma that was jet black inside and out.
>Coan et al. report, that " the green color in the shell is
>apparently due to algae within the shell matrix".
>
>Are there other shells with algae growing in the matrix? Any ideas
>on why some of the shells may be black?
>
>Rick Harbo
>Nanaimo,B.C., Canada
><mailto:[log in to unmask]>[log in to unmask]
All of the specimens I collected when I lived in Victoria, BC were
greenish. Those on the sides of the Oak Bay Marina floats in 1973
were large and particularly nice, as were the multicolored Mopalia. I
never did collect any P. cepio from low-light locations eg seacave
roofs or undersides of marina floats, where, if algae are the cause
of coloration, you would expect P. cepio to be paler or lack any
green tinge.
I have noticed that specimens of Anomia (possibly an unnamed species)
from under rocks and in dredgehauls from 40-70m off Dunedin, NZ can
be distinctly green. I have doubts that it is algae causing this in
either species, but I could be wrong. Algae would require porespaces
within the shell structure; these pores would have to be in contact
ie the shell woulkd have to be permeable for algal cells to get in
there. I don't know whether anomiids have porous shells. Gryphaeidae
do, and they don't have algae living within (ie they are porous but
not permeable).
As to the black color, this is typical of shells which have spent
time under anoxic conditions eg buried in mudflats. It is possibly
due to deposition of iron sulfides (marcasite) within the shell
structure, possibly replacing some of the calcitic or aragonitic
molecules.
--
Andrew Grebneff
Dunedin
New Zealand
Fossil preparator
Seashell, Macintosh, VW/Toyota van nut
‚ Opinions stated are mine, not of the University of Otago
"There is water at the bottom of the ocean" - Talking Heads
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