modern snail looks like heteromorph ammonites

hallucigenia

O. bimaculoides
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It looks stunningly like Nipponites! And the best part is that they're apparently always twisted the same ways -- it would be really interesting to watch their developmental trajectory and what it does to their ecological status. Might give some insight into the question "Why the hell did they get to be that shape?"
 

Neale Monks

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There are actually numerous gastropods that have uncoiled shells, most notably perhaps the infaunal, non-mobile Vermetid snails. These use long, whiskery threads to pull organic detritus and small prey into their shells for consumption. They're pretty common on reefs, and many people keeping marine aquaria will have seen their cobweb-like nets.

The problem is that there's no obvious reason why what a Vermetid snail does tells us anything at all about heteromorphs. Yes, both have uncoiled shells, but heteromorphs retain neutral buoyancy throughout their evolution, and there's no sign at all that things like spetae and siphuncle become degenerate, as would be the case had they become non-mobile or even simply animals that crawled about rather than swum or floated.

Cheers, Neale
 

Jean

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cuttlegirl;137449 said:
It's tiny, 1.5 mm high. Can you imagine searching for live snails that small? :bonk:

yes I had to do it this week for a mollusc lab on Wed!!!!! Not Vermetids but a teeny tiny bivalve called Modiolarca minutissima which gets o about 1.5 mm for a big one!!! So cross eyed :bonk: :bugout:, fortunately they like a common seaweed so at least I know where to look! Thank goodness for hand lenses! :biggrin2:
 

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