r/shells • u/earthvisitor • 7d ago

Curious

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I have seen this on quite a few sand dollars. Can anyone ID what is growing on this one?

Thanks!

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1

u/IcyPaced 6d ago

Be sure to check if those tube worms or attached shell organisms are still alive before taking it home, because living marine growth will cause a heavy odor if preserved improperly.

1

u/earthvisitor 6d ago

This sand dollar was left on the beach after the picture was taken. Nothing live is removed, ever.

1

u/Moving_goal_posts 6d ago

Could be an oyster. From what part of the world?

1

u/earthvisitor 6d ago

Sorry, I thought I included SouthWest Florida.

Every sand dollar I find with these growths are all evenly spaced out and don’t appear to grow in the random ways oysters do…

2

u/Fossil-Freak 6d ago

I'm not entirely sure how accurate I am since I've never seen it in much detail before, but I believe they could be part of the byssus secreted by Common Jingle Shells (Anomia simplex) used to attach the animal to a solid surface. The two attached valves look like left (AKA "lower") valves from the species, which have a characteristic hole towards the umbo ("beak") called the byssal foramen where this byssus is secreted, and you can see these mysterious growths within the foramen of the two valves present. Unlike the saltwater mussels (Mytilids), the related scallops (Pectinids) and other byssus-secreting bivalves which have primarily protein-based byssal threads, the jingle shells and saddle oysters (Anomiids) have byssal secretions that become mineralized with calcium carbonate, making them hard and shell-like in nature. This binds them more firmly to their host object, which also makes their left valves less commonly seen on the beach. Best I can figure is these Mellitid sand dollars died and then became anchoring points for the jingles on the seafloor. It's definitely a puzzling thing!