Calcium Content in Cephalopods

There is an important difference here between calcium carbonate, which is the calcium in shells and cuttlebones, and ionic calcium (calcium chloride most commonly when not free ionic) used in neurons and other cells. Even cephs with no calcified structures need calcium for cellular functions, like all animals.

About the speculation of high Ca2+ in tissue because of the 'rich' innervation - I have some doubts about this. Lots of other peripheries have very, very dense innervation (mammalian skin and body hair innervation, for example, is pretty darned extensive). Yes, cephalopods use their motor neuronal network to show off with chromatophores, and they do have a LOT of peripheral cell bodies in the arms, but I will bet you mammalian tissue rivals it.

Mammals absorb their calcium via their diets, and (presumably) cephalopods do too - I actually don't know for sure.. I guess they could absorb it directly from SW... But animals generally have no trouble getting enough of it from a regular dietary source without extra supplementation. In captivity, where food sources are far more homogenous than in the wild, supplemental calcium might be needed (just like it is in humans with bad diets...). For animals needing to make a shell in captivity (like Nautiluses), calcium supplementation might be necessary.

The original observation that calamari supplies a significant amount of daily calcium - I'm guessing this is common to many marine food sources.

About the marine-freshwater transition - it seems unlikely that calcium needs are a limiting factor. Many molluscs (with highly homologous physiologies and similarly substantially complex nervous systems) have colonised freshwater habitats just fine. I'd love to know why cephalopods never made it to freshwater, too. Any more thoughts on that topic?
 
thanks for the detailed reply, but i wasnt really concerned with cephalopod dietary needs. my thinking was that if cephalopods had high concentrations of calcium in their tissues, it might mean that the had a hard time excreting excess ions like calcium. a weak renal system might be the the barrier that kept cephs out of freshwater.
 
Pr0teusUnbound;194801 said:
thanks for the detailed reply, but i wasnt really concerned with cephalopod dietary needs. my thinking was that if cephalopods had high concentrations of calcium in their tissues, it might mean that the had a hard time excreting excess ions like calcium. a weak renal system might be the the barrier that kept cephs out of freshwater.

Well I wasn't entirely sure what your primary interest was, so I gave a general reply to the major themes in the thread, not just your original post...

Have you read this thread? It contains some interesting discussion on the freshwater question, including several excellent walls-of-text from Monty.

Re-reading over his old posts always make me sad initially, but then very happy that his thoughts are still here with us!

http://www.tonmo.com/forums/showthread.php?10350-Freshwater-squid
 
I think I could spend a solid month of 9-5 reading of this site, & still not be half-way through! I wish I would've been around here in Monty's time; he seemed to be quite a wealth of information. Definitely wove well into the tapestry. Those posts are well worth a look-see, pr0teusUnbound!
 
CG thanks for the article on decay. The observations of postmortem swelling and some of the pre-death observations (keep in mind my lay background and lack of biology) make me, again, note the swelling I often see in the arms during senescence (and an odd swelling I am currently seeing in Octavia of one arm - potentially an infection, but different than any I have seen). It also made me think to mention the infertile eggs that I kept in saltwater for months. The eggs' water dried out occasionally (ie were left covered in salt) and I added more saltwater (not fresh water) when I noticed but the odd thing was that they never seemed to change. The salt may have preserved them as we do with meat but they never swelled or appeared to shrink and when I re-added water the looked and felt just as they had (to the naked eye and untrained touch) when I collected them. When I have placed emptied casings in saltwater, they have deteriorated so I found this very strange but it makes me wonder if infertile eggs may preserve given the right conditions. Unfortunately, they might not tell us much.
 
robyn;194804 said:
Well I wasn't entirely sure what your primary interest was, so I gave a general reply to the major themes in the thread, not just your original post...

Have you read this thread? It contains some interesting discussion on the freshwater question, including several excellent walls-of-text from Monty.

Re-reading over his old posts always make me sad initially, but then very happy that his thoughts are still here with us!

http://www.tonmo.com/forums/showthread.php?10350-Freshwater-squid

my apologies. i can be vague at times.

i have read a bit of that thread. i liked how someone mentioned bull sharks. i remember hearing on shark week that the can transition from saltwater to freshwater by hiking their testosterone levels, and salmon do the same thing with their cortisol, so im rather convinced a strong renal system is important for salt-freshwater transition.
 

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