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Discussion Starter · #1 ·
so I found this snail/conch looking thing in my tank tonight. It has a black fuzzy looking shell, around another shell. When I pulled it out, the black cover pulled back and I saw the other shell thing... what is this thing?


 

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Looks like it is probably a cowrie. Very cool. The outer fuzzy looking layer is the mantle, which it can extend out to completely cover the shell.

Ever wonder why cowrie shells are so smooth and shiny all over the outer surface, while most snail's shells are only shiny on the inside? The shell is secreted by the mantle. The mantles of most snails only cover the inside of the shell, and new, shiny smooth shell is only built up on the inside, and, especially, along the edge. This is how a snail shell gets bigger. Cowries (and some other snails) secrete new shell all over the surface, resulting in the shell always looking fresh and smooth and polished all over.

I must say though that I have never quite understood the method by which cowries make their shells bigger as they grow. Based on how the shells are shaped, it has never seemed to me that is could be as simple as adding new shell along the leading edge (which is the main thing that most snails do). It probably is not all that mysterious, but I have never watched a small one grow bigger and observed how its shell shape changed, and I have never seen a cross-section of a cowrie shell.

You are probably wondering what your cowrie is eating and whether it is safe to have in your tank. My answer is...I don't know. My sort of vague recollection is that some species are herbivores, while others tend to feed more on sessile invertebrates of certain types (?). My guess is that if you have had this snail for a while and nothing you care about has been getting eaten, then I'd guess the cowrie is probably safe to have in your tank. It is certainly a cool snail.

I had a tiger cowrie once for a short while. I think it died of starvation. I never saw it eat anything. Very sad.
 

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It looks like a Cowrie to me to. I haven't seen that one before. There are a lot of Cowries that carnivores and a few that are herbivores. I would isolate it until you can get a positive identification.
 

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Discussion Starter · #4 ·
I found this guy on the overflow with the rest of the snails, mowing down algea. I will keep him out of the display for now. Does anyone have links to sites that I can read up, and maybe find a positive ID?
 

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OK, probably I'm the only person who has been troubled by this puzzle (the question of how cowrie shells develop), but this thread got me wondering and when I wonder about things these days I'm increasingly prone to go to Google.

Turns out cowries start out life growing their shells pretty much like any other snail, building up new shell along the margin. The shell is coiled like any other ordinary snail at this stage (actually, apparently they look a lot like olive snails when they are immature). Then the margins of the opening are modified and develop a sort of folded over shape (this folded over margin is what always puzzled me...I never understood how the shell could grow bigger with this shell shape), and the margin of the opening develops tooth-like ridges.

This can be seen on the following web page: http://www.hans-rothauscher.de/kauri.htm

I realize that this probably was not troubling anyone but me, but here it is anyway!
 
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