In cephs, the cells have a greater salt concentration than the surrounding fresh water. Water enters the cells in an attempt to reach equilibrium and the cell walls burst - eventually killing the organism.
animals that move between fresh and salt water have ways of maintaining the water/salt content of their cells.
Ok, the ceph's cells need keep a salt concentration gradient, isn't it?
If you put it in a fresh water, the gradient changes, the fresh water get into the ceph cells for re-equibrate cell gradient, and the poor bug, finally bomb off!!!
The old myth of crocodiles shedding tears for their prey comes from the fact they have glands for removing excess salt near their eyes. Bull sharks often go hundreds of miles up river from the ocean here in Mississippi (one was caught on rod and reel north of St Louis).
And what do you want to say with it? ( is nice info but I think not relevant here). Cephs can have very different kind of cells. Maybe sharks can do it, and also the humans can do the oposite to it. Why have the cephs be the same like another animals?
Do you have another teory.
P.D: Sorry maybe I have sound too rude, but my english is limited. Sorry.
There are plenty of molluscs that have adapted to a fresh water existence, slugs and snails even made it on to land, but cephalopods for one reason or another over the almost 480 million years of their evolution have done neither. The same applies to echinoderms; an entire phylum sealocked. This could all change one day, but it simply hasn't yet. It may only take a few random quirks to the genome and Bob could very well be your uncle.
Nope, not changed again. It is still Enteroctopus. It's just that we tend to use the generic names interchangeably. It's alright; we all know what we are talking about. There are a group of species in this genus Enteroctopus: E. dofleini, E. zealandicus (NZ), E. megalocyathus and E. magnificus; there are probably a suite of other species that could be assigned to the genus - I have seen a number from Australia and the South China Sea that might be new species (they might not be as well .... there's a lot of work that needs to be done in this genus).
Characters/character states that can define this genus are: large size, subequal arm length, similarly sized and enlarged suckers on all four arm pairs, large posterior salivary glands, reduced-to-absent diverticulum of the crop, exaggerated penis diverticulum length, absence of membranes between renal tissue and ventral inner surface of mantle, and exaggerated length of calamus of hectocotylus. Much of this might seem alien to most, but these characters/states are common to all species of this genus; it seems to be rather primitive, in that it shares many characters/states in common with more 'bathypolypodine' forms.
Lol, were all ceph nuts so knowing a lot about them makes a lot of sense. But yea, basically what you asked has been covered I hope. Then there's that rumor about that fresh water octopus...most likely false though.