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First time posting! :-)

I've been hunting around for "urban fossils" in my city. I'm really used to seeing rudists everywhere, and whenever I come across anything else (like a piece of coral or a gastropod) I get excited.


Today I saw something I had supposed was a gastropod shell section (now I'm not so sure), but it has a peculiar design, and I wonder if anyone can tell me what this design is. It seems to be some kind of internal structure in the shell?


I'm attaching two photos of a close up of two different specimens and then a broader picture of another part of the slab, in case anything else in there might give people hints. 

The photos were taken in Donostia, Spain. I can't really say where the rock was quarried, but I guess somewhere in Spain?


I'd love to hear your take on it! (Both on the "internal structure" and what kind of creature this might be)


Thanks :-)









Edited by elizgoiri
Wanted to rephrase something. Then someone else's photos appeared in my post (???) and I had to delete them
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Wow, great!! Yes, they do look like the same type, with those oddly convoluted walls (plaits)


Thanks to your reply I was able to find a bit more about the function of these "plaits" from the article

Kollmann H. A. 2014. — The extinct Nerineoidea and Acteonelloidea (Heterobranchia, Gastropoda): a palaeobiological approach. Geodiversitas 36 (3): 349-383.



The internal plaits of the Nerineoidea had different functions: the columellar plaits subdivided the columellar muscle into strands, which allowed portions of the foot to be moved individually. A tubelike space delimited by the parietal and palatal plaits is compared with the pallial caecum or posterior mantle chamber of heterobranchs and served the respiration. Waste from both mantle chambers was expelled through a subsutural notch, which is the common feature of the Nerineoidea. The Nerineoidea were shell draggers and probably deposit feeders with a semi-infaunal mode of life.


(Just from the article summary -- not sure my brain can handle the other 36 pages!)


Thanks a lot!! The perks of jury duty... :-)





Edited by elizgoiri
fixed DOI link
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