Pycnodonte oyster pearl or growth (Cretaceous)

[frankh8147]

Greeting!

 

I found this Pycnodonte yesterday in Monmouth County NJ (Cretaceous) with this strange growth on it (the bump). I compared it to about two dozen of my other Pycnodontes' and did not see anything similar so I was wondering if this was their version of a pearl or if it something else. As always, all help is greatly appreciated!

-Frank

[frankh8147]

For comparison, here are some Pycnodontes'...

[Innocentx]

Yes. I would agree it's probably a growth reaction to injury.

[ynot]

Commonly called "blister pearl".

Nice find.

[abyssunder]

I agree with the others.

Nice examples are also in this older topic:

BTW, some of your oysters have nice borings, caused probably by clionaid sponges.

[frankh8147]

That's great to hear, thanks everyone! I've read about these in the past and was hoping that would be the case.  

[abyssunder]

" Pearl Formation
The formation of blister and free pearls in bivalves has often been linked with parasitic flatworms (Conway-Morris 1981; Combes 2001; Littlewood and Donovan 2003; Boucot
and Poinar 2010). Nevertheless, various other parasitic organisms such as fungi, unicellular organisms, nematodes or arthropods (and their eggs) as well as various other irritants including inorganic material which get stuck between mantle and shell can induce pearl formation (Götting 1974, 1979; Lauckner 1983). Nevertheless, the morphology of some parasite-induced structures in extant bivalves are believed to be very specific to parasitic flatworms such as pits in shells and igloo-shaped shell secretions or to polychaete worms such as borings and can be traced back in the fossil record (Liljedahl 1985, Ruiz and Lindberg 1989; Ituarte et al. 2001, 2005; Huntley 2007; De Baets et al. 2011). Blister pearls (Fig. 20.1f) in ammonoids have therefore often been linked with parasitic infestations (House 1960; Keupp 1986; Hengsbach 1996; Davis and Mapes 1999; De Baets et al. 2011, 2013b). Furthermore, the fact that blister pearls (cephalopods, bivalves, and gastropods) and free pearls (bivalves, gastropods) are known from a wide variety of fossil and extant taxa (Binder 2002; Boucot and Poinar 2010 and references therein) suggest that every shelled mollusc is capable of forming such structures (Landman et al. 2001). In the fossil record, these pearls can be preserved as pits on internal moulds (steinkerns). "

 

excerpt from K. De Baets et al. 2015. Parasites of Ammonoids in C. Klug et al. (eds). Ammonoid Paleobiology: From anatomy to ecology. Topics in Geobiology, vol 43: 837-875

 

Just for comparison, take a look how close could they be.

 

[frankh8147]

@abyssunder very interesting comparison, and I agree, very similar. Thank you!

[abyssunder]

You are welcome!