Re: Cephalopod parasites

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North American oyster fisheries are adversely affected by (amongst others) 
`mud worms' (_Polydora_websteri_) which form so-called mud blisters by two 
separate processes: by boring through the shell; and by inserting 
themselves between the mantle and the shell.  The oyster's response is the 
same in both cases: it secretes a thin shelly deposit over the worm.  This 
is bad for the commercial fishery, but makes an excellent refuge for the 
worm.  Perhaps something similar to the second scenario was happening with 
Neale's ammonites?

Ref: Haigler, S. A. 1969.  Boring Mechanism of _Polydora_websteri_ 
inhabiting _Crassostrea_virginica_.  American Zoologist, 9(3 ed.2): 821-828


>David Campbell writes:
>        The inclusions in Pliocene Mercenaria (also found in various other
>venerids, Recent and fossil) are calcite patches without any macroscopic
>surface relief.
>        Blister pearls are a fairly common response to parasites or other
>foreign debris.  A Crassostrea virginica I obtained from the local seafood
>market for DNA analysis has a blister pearl with no obvious external
>association, although there are numerous clionid-like holes in the outer
>layer.
>
>David Campbell   "old seashells"
>Department of Geology
>CB 3315 Mitchell Hall
>University of North Carolina at Chapel Hill
>Chapel Hill NC 27599-3315
>bivalve@email.unc.edu