[neilep (OP)]

Dearest Celaphalopdologists,
Meet Arbuthnot Saline The 3rd. He's a happy chappy living the ocean life, carefree , nonchalant and a bit of a player !!

But, there is one thing that bothers him, he's got no cousins that live in fresh water ? why's that then ?

Why are there no freshwater squid, octopi,  etc etc ?






Arbuthnot ' Spearheading' the campaign (pun intended) to lay down the foundation for a freshwater cephalopod community.

[evan_au]

According to this article, cephalopods lack the sodium pump that is required to prevent them turning into an osmotic balloon in fresh water.
https://www.abc.net.au/science/articles/2013/01/16/3670198.htm

the brief squid, Lolliguncula brevis, found in Chesapeake Bay, is a notable partial exception in that it tolerates brackish water.

So, to maintain their trim, jet-propelled, ocean-going shape, they have to stay in salty water.

[alancalverd]

Same reason there are no oceanic apes, I guess.Each to his own ecological niche!

[neilep (OP)]

According to this article, cephalopods lack the sodium pump that is required to prevent them turning into an osmotic balloon in fresh water.
https://www.abc.net.au/science/articles/2013/01/16/3670198.htm

the brief squid, Lolliguncula brevis, found in Chesapeake Bay, is a notable partial exception in that it tolerates brackish water.

So, to maintain their trim, jet-propelled, ocean-going shape, they have to stay in salty water.

Thank ewe Evan, that's a very interesting article.

So, a sodium pump is needed. Fascinating.

Freshwater dwellers have salty blood relative to the water around them

Dragons Den here we come !

[neilep (OP)]

Same reason there are no oceanic apes, I guess.Each to his own ecological niche!

There may have been at one point https://listverse.com/2019/03/04/10-reasons-to-believe-we-have-aquatic-ape-ancestors/

[Deecart]

I do not totaly agree with the explanation : "Octopodes do not have sodium pumps, so they can not live in fresh water."
In my opinion, saying that octopodes find a better environnement in the sea and they have enougth room in sea so they dont need to colonize (evolve in) other dangerous environment is a better answer (sodium pump is a very basic structure every living being could develop with time).

[evan_au]

sodium pump is a very basic structure every living being could develop with time

But you can lose a functioning gene much more rapidly than you can regain a lost gene.

[Deecart]

But you can lose a functioning gene much more rapidly than you can regain a lost gene.

Yes, but when you speak of millions of years with numerous populations, the probability to regain an interresting gene can become high.
1. You dont need to totally reinvent the gene, it is possibly already present but not expressed (what is not expressed remain because there is no selection, or in this case less selection (we have indeed selection due to the optimisation of the quantity of usefull ADN but it takes much time to do so)).
2. There is the possibility to have transmission of the gene from an other specie, and this is what we call "horizontal transfer" (this process is total acknoleged for procaryotes, but recent studies shows that this could also be more widely the case within eucaryotes).

"Sequence comparisons suggest recent horizontal transfer of many genes among diverse species including across the boundaries of phylogenetic 'domains'. Thus determining the phylogenetic history of a species can not be done conclusively by determining evolutionary trees for single genes."[82]

https://en.wikipedia.org/wiki/Horizontal_gene_transfer