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Ay up

Chicken

Hatchling
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Feb 15, 2007
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4
#1
Finally got myself registered here (Thanks Tony) I've Been meaning to post for ages on the Spirula as I'm doing my geology masters thesis titled "the Isotopic variation in Spirula spirula: a key to understanding the ecology of fossil cephalopods"
I've basically undertaken carbon and oxygen isotopes from throughout the shell, SEM of the shell (specimens from Perth, Oz) and I also have several complete specimens kindly donated by the Natural History Museum that I aim to dissect and if possible, hopefully to x-ray one or two.

Cheers,
Chris
 

tonmo

Titanites
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#5
Definitely glad to have you aboard! :cuttlehi:
 

monty

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#6
:welcome: to TONMO! I've been trying to drum up discussion about the taxonomically wacky critters like spirula lately, so I'm glad to hear there's another person on board who's an expert!
 

Chicken

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Feb 15, 2007
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#7
Thanks for all the hellos.
I'm studying Mgeol at the Universtiy of Plymouth, UK. Things are pretty hectic right now, but as soon as I get a chance I'll try to post a summary on some of the available literature, but that will most probably be early April (fieldtrips etc).
I've pretty much got all papers written on Spirula, so if there's anything anyone needs to know, you're more than welcome to give me a shout and I'll see what I can do. Most unfortunately are paper copies, but some are pdf's which I'm more than willing to share (if allowed on this board).

Well back to work, hope I can contribute more soon.

Cheers
 

Steve O'Shea

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#8
:welcome: Chris. A most interesting subject you have chosen! A friend here did a micro-CT of an entire Spirula .... just for something to do (he's arather interesting chap). It's pretty impressive. PM me if you'd like to be put in touch with him; I'm sure he'd forward the images and interpretation to you.

I have one question to begin with.

Is there a vacuum in that shell or not? Someone told me it was vacuum, but I always thought it was pressurised (and would think a vacuum would lead to implosion).
 

Carl J. Bobrow

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Feb 24, 2004
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#9
No vacuum gaseous filled with a siphuncle like a Nautilus

Wiki says

he siphuncle is a strand of tissue passing longitudinally through the shell of a cephalopod mollusk. Only cephalopods with chambered shells have siphuncles, such as the extinct ammonites and belemnites, and the living nautiluses, cuttlefish, and Spirula. In the case of the cuttlefish, the siphuncle is indistinct and connects all the small chambers of that animal's highly modified shell; in the other cephalopods it is thread-like and passes through small openings in the walls dividing the chambers.
The siphuncle is used primarily in emptying water from new chambers as the shell grows.[1] Essentially what happens is the cephalopod increases the saltiness of the blood in the siphuncle, and the water moves from the more dilute chamber into the blood through osmosis. At the same time gas, mostly nitrogen, oxygen, and carbon dioxide, diffuses from the blood in the siphuncle into the emptying chamber, filling it up with gas. Note that the cephalopod does not pump up the shell; the gas moving into the chamber is a passive process, instead the energy is used in absorbing the water from the chamber.


An image showing the siphuncle, the tube which connects the current living shell to the previous ones.
Removing water from the chambers of the shell reduces the overall density of the shell, and thus the shell behaves as a flotation device comparable to the swim bladder in bony fish. Typically, cephalopods maintain a density close to that of sea water, allowing them to swim with the minimum of effort. In the geologic past, many cephalopods grew to an enormous size (over ten meters in length) thanks to this.
Generally, the siphuncle is unable to provide a way to change the density of shell rapidly and thus cause the animal to rise or sink at will; rather, the animal must swim up or down as required.
The siphuncle found in fossilised cephalopods is assumed to have worked in the same general way. The siphuncle itself only rarely gets preserved, but many fossils show the holes, called septal necks (or siphuncle notches), through which the siphuncle passed. In most fossil nautiluses, the siphuncle runs more or less through the center of each chamber, but in ammonites and belemnites it usually runs along the ventral surface. In some fossil straight shelled nautiluses cylindrical calcareous growths ("siphuncular deposits") around the siphuncle can be seen towards the apex of the shell. These were apparently counterweights for the soft body at the other end of the shell, and allowed the nautilus to swim in a horizontal position. Without these deposits, the apex of the buoyant shell would have pointed upwards and the heavier body downwards, making horizontal swimming difficult. The siphuncle of the Endocerida also contained much of the organisms' body organs
 

cuttlegirl

Colossal Squid
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#10
Carl J. Bobrow;132369 said:
In the case of the cuttlefish, the siphuncle is indistinct and connects all the small chambers of that animal's highly modified shell;
I wouldn't call it indistinct, it is a membrane covering the ventral portion of the cuttlebone. It is a flat membrane instead of a tube...
 

Carl J. Bobrow

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Feb 24, 2004
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#11
Point well taken... though me thinks the author was referring to the fact that it is not in plain sight or easily distinguishable as with Nautilus or Spirula...
 

cuttlegirl

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#12
Still, if you dissect a cuttlefish, it is the membrane covering the ventral portion of the shell. Maybe it is the fact that the membrane functions as a siphuncle and produces the shell.
 

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