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Malacology - H.G. Wells Style

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Dec 24, 2002
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Phil,

Thanks a lot! I wouldn't doubt the annelid-mollusc link. An old invert. zoo instructor I had was a little too cladogram-happy, BUT his links between phyla did pique my interest.

The "cap" shapes I'm assuming are shells? Maybe ancestors of the Monoplacophora? I still think that there may be a distant relation between the Molluscan Aplacophorans and Caudofoveatans with the coelomate worms like the Sipunculans and Echiurans... Any thoughts out there? The "aps" and "cauds" are more "simple" (*shudders*) but I have no idea if they're more ancestral or derived.

Sorry about the shuddering :biggrin2: Its just that I have found myself defending evolutionary theory lately to more and more people and many either cannot or will not (more likely the latter) try to understand that "simple" and "complex" are pretty relative terms in evolution and that forms evolve to suit the best niche. Heck, look at parasitic copepods! They are SOOOOO simple in form yet are the product of countless generations of specializations. For a really creepy crustacean, look up the Rhizocephalan. It starts out a cyprid, and ends up a decapod's worst nightmare... I doubt even H.R. Geiger could come up with something that scary - and he created the Alien.

Sorry about the rant, and I mean no offense to you by it. I always use the words "simple" and "complex" and seem to get them thrown in my face again... :lol: I can imagine my old zoology instructor spinning in her grave... and she's far from dead! :lol:

Interesting thing about the early ceph. Kind of a "gastro-ceph". I wonder what intermediate forms looked like? If you have any more mollusc art links, can you hook me up? Thanks again Phil!

Sushi and Sake,

John
 
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Addedum: I think that the Caudofoveata bear some more investigation. An annelid link sounds pretty reasonable too. I think it would have to do with the chaetae-like structures mentioned earlier. "Cauds" also have imbricating calcareous(?) scales and/or spicules....

Hmm... definitely a pattern forming here...

As far as the cephs and their forms and history go, his leads to a very interesting thought; the diversity of the molluscan bauplan and its evolutionary history leads me to believe that they were once pretty much large and in charge, right? I mean, adaptive radiation of this sort seems to mean a dominant spot in the ecosystem if I'm not mistaken. Any thoughts out there?

(Sorry if I'm sounding like an overexcited kid here. Keep in mind, I'm not a malacologist, let alone a zoologist... Yet! :lol:)
 

Architeuthoceras

Architeuthis
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I think the Ordovician period was the age of Nautiloids (Molluscs), 500 to 440 mya. The largest animal on earth was a 9 meter (30 ft) endocerid (that number is probably passed around like the 60 ft architeutis). There were more familys of cephalopods then than any other time in earth history. Their radiation was possibly in response to being able to float above their food source, Trilobites. And as fish started to appear in the next couple of time periods the nautiloids began to diminish. I think most of the other molluscs had a great radiation in the Ordovician as well.

:nautilus: :snail: IMHO
 

Steve O'Shea

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NINE METERS :!: :!: :!:

Kevin, we've got to get to the bottom of this!!!! I am rapidly losing interest in Recent cephalopods!!! Can you provide further details?
 
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Okay, NOW I'm embarassed.... what is an endocerid?

*looks it up*

Well... Now I know... Darn, shoots my pteropod theories out of the water. I still think that there is more than meets the eye here. What does a 30 ft endocerid eat (besides the obvious answer -- "anything it wants")? Somehow I wonder just how much more diverse the mollusc bauplan was before? Just HOW many forms did they take?

Strange... cephs have become so streamlined in design... Without the teleosts, they might have been even more of a dominant force in the oceans. Or maybe they are yet to have their time in the proverbial sun.

*yawn* Only time will tell...

Sushi and Sake,

John
 

Phil

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John,

Thanks for the info about the Rhizocephalan. I know one shouldn’t be emotive about behaviour patterns but what a horrific creature! Hadn’t heard of that one before; much to my regret I read about it whilst eating a prawn sandwich. Bad idea.

Going back to the origins of the mollusca there have been a few interesting finds in recent years, notably a strange beast known as Kimberella that was described about five years ago and was discovered at the White Sea in the Arctic circle on the north coast of Russia and dates to about 550mya. This places it almost immediately before the Cambrian ‘explosion’ that gave rise to modern bauplans in a remarkably short space of time. (hotly debated, most estimates say about twenty million years). Kimberella is interesting as it is difficult to interpret but is thought to be an early mollusc. Physically it looks like a jellyfish without the tentacles but has bilateral symmetry and a tough (non-mineralised) but flexible shell. Some fossils apparently display a mollusc type foot and although no radula has yet been found associated with this animal, as far as I know, not all mollusc fossils do.

Trace marks and scrape marks in some late Precambrian sediments may well have been caused by a creature such as this or even its ancestor. Trace marks date from 565mya or even earlier so there must have been some ancestral creature that lived in a mollusc fashion scraping up algae at this even earlier date possibly as far back as 620mya.

Other early (probable) molluscs are evident in the Tommotian faunas from Siberia (about 530mya) which largely consists of many tiny shells, many of which resemble monoplacophora. There are many varieties of cone, spiral, horn-shape and tube evident though whether or not they were molluscs depends on how a mollusc is defined, I suppose. Try doing Google searches under Tommotia, Yochelcionella or Latouchella if interested. Following this is the sudden evolution of modern body plans during the Cambrian ‘explosion’ including the arthropods and although probable molluscs were evident (re: Wiwaxia above) the relationships of these creatures to each other animal groups has been the source of much debate and study recently. All very complex.

I still have not discovered a cephalopod earlier in date to Plectronoceras (Upper Cambrian). I attach a copy of its anatomy here. I had to copy it from a text book to avoid copyright problems duplicating it here. It is quite probable that Plectronoceras evolved from something very similar to Latouchella as they do look similar (from drawings in textbooks, that is!)

On a different note, I think that 10m long Nautiloid was called Cameroceras. Must look that one up.

Phil

(PS If I have made any mistakes above I apologise. I have never actually studied zoology or palaeontology and am working out of a few books at home. All very interesting, isn’t it!)
 
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Phil,

HA HA HA HA!! :lol: Well, if it makes you feel any better, the favorite host of Rhizos seems to the "dungees" (Dungones Crab(sp?)) Cancer magister here.

Yeah, the Rhizocephalan is a +100 on the freaky scale... but nontheless a miraculous lifeform. Just a testament to the power of life and its many forms. How hardy life on Earth can be!

Thanks for the info and the pic... I'm going to find some more information, now that I have some (scientific names).

Sushi and Sake,

John
 

Architeuthoceras

Architeuthis
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Steve,

I can't find a specific reference to the 9 meter (30 ft) Endocerid, but almost any book on fossil cephalopods quotes that number. Even Teichert (1964, Treatise on Invertebrate Paleontology, Pt K, Mollusca 3,) mentions The 9 to 10 meter number only in the introduction to a couple of chapters. Manger, Meeks, and Stephan, 1999, Pathologic Gigantism in Middle Carboniferous Cephalopods, Southern Midcontinent, United States, in: Advancing Research on Living and Fossil Cephalopods, edited by Oloriz and Rodriquez-Tovar, Kluwer Academic/Plenum Publishers, have a nice summary of giant fossil and extant cephalopods with many specific references (but they only refer to Teichert for the 9 meter Endocerid). The longest Endocerid I have found is only 450mm. You can see a picture of an Endocerid on my web site

http://ammonoid.topcities.com/whiterock.htm

:nautilus:
 

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