Malacology - H.G. Wells Style

[Fujisawas Sake]

Hi,

Well, this thread is my split and an apology for getting off the previous subject of "Why Are the Giant Squid so GIANT?". A little background: I was curious about what the past held for cephs (their evolutionary lines, especially ammonites - SERIOUS controversy there), as well as what size and forms cephs have today and what shapes they may take in the future.

*ahem* Anyway... When last we left off, I was wondering about the possibility of ammonites being paraphyletic, or just what form or forms they could have taken, as well as the weird "The Future is Wild" idea of land squids and such. Only time will tell....

 

[Phil]

Hi.

I think you will enjoy these fantasy constructions of possible ammonite descendants:

http://users.macunlimited.net/n.monks/ammonites.html

Neale Monks is a palaeontologist at the Natural History Museum in London who specialises in ammonites. I'll write something a bit more detailed soon (bit busy at the momnent, for once).

Phil

 

[Fujisawas Sake]

Schweet! Thankee-sai, Phil!

Well, I'll click on that link ASAP. I was hoping to find some more info. I have an invert zoo text that might be helpful. Its at home, which is about 1800 miles away right now

Steve, if you read this post: I was thinking about a land walking Ceph a-la "The Future is Wild"... At the 100 million year mark is the Swampus, which can survive for up to four days out of the water...

Here's my two cents: What about the evolution of a closed, negative-pressure mantle, and a "book lung" modification of the gills? I guess it would be a type of pulmonate ceph, and it would have to be small, but if the mantle was modified into a "lung" like the pulmonata, it could be done. As far as movement, muscular hydrostats only go so far, but a small form might make it. Any thoughts?

Sushi and Sake,

John

 

[Steve O'Shea]

It is possible (this lung business), but that there terrestrial squid would be one lethargic thing; not sure what sort of acrobatics pulmonates can get up to, but I don't think they're the most exciting (behaviorally) of molluscs. Probably the lungs ratio of surface area (for O2 absorption) to volume would not allow the terre-squid to get up to much, except maybe chase fungii.

Having said this, a colleague at work recently returned from a wee trip to collect copepods from leaf litter ... and basically dry leaf litter at that. In minute droplets of water on these very dead leaves she found a startling diversity of copepods (I wouldn't have thought it possible). So, maybe, just maybe, a small octopus-like animal could slither its way through more moist leaf litter in some futuristic rain forest environment. Just one problem, and that is no ceph occurs in fresh water, but so as long as it rains salt, the ground is salty, or the ceph one day can tolerate non-marine conditions then you just might encounter them. If you do I sure hope they have the equivalent of the rattlesnakes thingymajig, coz I'd like to know if something like that was slithering around my toes.

Phil, I think we're going to have to design our own ammonites!
Cheers
O

 

[Fujisawas Sake]

Steve,

Actually, that doesn't surprise me. Copepods are one of the most adaptive Crustacean groups you can imagine. They're also found in peat moss as well as marine and freshwater habitats. Also, the Phylum Tartigrada (water bears) are always good for a few "oohs" and "ahhs" (as well as the occasional "Aww, that's so cute!") from a class, and they're found around areas like that. If you have the time, study the body plans of the parasitic copepod species... WOW!!! I mean, talk about bizarre.

Discovery Kids had a ceph special today, and showed a very diverse selection of ammonite shell designs. They also mentioned the belemites, which seems to point out squid evolution, but I'm wondering about the Octos and Vampyros and such... I wonder when they came about?

Anyway, I'm absolutely STOKED!! I went to the Houston Museum yesterday and saw a maned wolf, Chrysocyon brachyurus. Its a really tall canid that hunts in tall grasslands in South America. I've only seen them in pictures! I took some photos! I can't wait to get home and download them from our digicam.

Well, I may not be posting until Friday, as I have to head back to California tomorrow. If I don't see you before, have a great New Years!

P.S. "Rattlesnake Thingumajig"?

 

[Steve O'Shea]

.P.S. "Rattlesnake Thingumajig"?

You know, the bit wot rattles down the non-bitey end (not quite the blunt end - snakes seem to have two pointy ends ). What do you call it? A rattle? Must have a better name than that - the dictionary describes it as "loose horny segments on the tail", but I'm sure someone has come up with a more techo term than rattle.
O

 

[Fujisawas Sake]

Its pretty much "rattle"... sorry... If it makes you feel better, the rattlesnake subfamily (Family Viperidae, Subfamily Crotalinae) is considered the most advanced species of Viper.

 

[Fujisawas Sake]

Steve,

Here's the skinny on "The Future is Wild": The big 8-ton land walking squid is a biomechanical puzzle... I read the companion book to the series, and while I get it, it does sound wonky at best. Using a system of circular and vertical muscles to compensate for skeletal muscles....
W E I R D ....

Honestly though, do you see freshwater tolerance as a future step for cephs? I mean osmoregulation aside. What about communal behavior?

 

[Fujisawas Sake]

Oops.. another thing:

How old is the Phylum Mollusca? Around what period did they appear?

 

[Phil]

How old is the Phylum Mollusca? Around what period did they appear?

That is indeed a very interesting question. Mollusca are represented in the early Cambrian period (550-490 mya) in very simple cap shapes, though most of the 'modern' forms of mollusc appeared during the late Cambrian/early Ordovician radiation. What is debated, as far asI know, is whether the 'later' more complex forms represent a continuation of the early lineages or whether the early Cambrian forms were not directly ancestral.

One fascinating creature worth looking up was a strange creature called Wiwaxia that has been found in rocks of middle Cambrian date (525mya). This creature was hump shaped, had a foot like a mollusc and was covered in scelerites or scales with two rows of spine-like blades running across its back. It was believed to be a very primitive mollusc though recent work has placed this creature on the lineage that led to the annelids. Microscopic studies of the scelerites reveal basic structural simularities to the chaetae (stiff hairs or bristles used in locomotion) in polychaete worms. From this it seeems that the molluscs and annelids may have a close ancestral affiliation in the early Cambrian. As for what the actual common ancestor looked like, no specimen has yet been found and educated guesses can only be made as its appearance.

As for cephalopods, the earliest creature that I am aware of was called Plectronoceras which dates from the upper Cambrian and was found at Shantung in China. Shells of this 2 inch long tiny creature were horn shaped but show clearly defined chambers with a siphuncle. A reconstruction I have depicts gills, tentacles and the classic molluscan foot. It was believed to be a creeping bottom dweller as opposed to being an active swimmer.

Hope this is of some interest, Phil

 

[Fujisawas Sake]

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 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... I can imagine my old zoology instructor spinning in her grave... and she's far from dead!

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

 

[Fujisawas Sake]

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! )

 

[Architeuthoceras]

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.

IMHO

 

[Steve O'Shea]

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?

 

[Fujisawas Sake]

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