[Coral-List] Thread submission

[Douglas Fenner]

    That is a good question, I don't know that there is any answer at this
point.  Certainly there are fresh water gastropods and bivalves, but to my
knowledge there aren't any fresh water chitons (polyplacophora),
aplacopherans, scaphopods (tusk shells), or monoplacopherans.  See
https://en.wikipedia.org/wiki/Freshwater_mollusc  So at the class level,
there are more Mollusc classes that are restricted to salt water than there
are that have entered fresh water.  The main challenge probably is
osmoregulation, regulating salt content and water content of the body and
cells.  The Wikipedia article on freshwater molluscs says that they have
characteristically low tissue salinities and some of the freshwater clams
have the lowest tissue salinities known.  So they are tough and tolerant of
low salts, instead of being good at regulating salts.  Of course gastropods
(snails and slugs) make it onto land, there are lots (most are pulmonates,
they have lungs instead of gills), but none of the other classes make it
onto land.  The Wikipedia page on Cephalopods
https://en.wikipedia.org/wiki/Cephalopod  says that "None of them can
tolerate freshwater <https://en.wikipedia.org/wiki/Freshwater>, but the
brief squid, *Lolliguncula brevis
<https://en.wikipedia.org/wiki/Lolliguncula_brevis>*, found in Chesapeake
Bay <https://en.wikipedia.org/wiki/Chesapeake_Bay>, is a notable partial
exception in that it tolerates brackish water
<https://en.wikipedia.org/wiki/Brackish_water>.[4]
<https://en.wikipedia.org/wiki/Cephalopod#cite_note-4>" and "Cephalopods
are thought to be unable to live in freshwater due to multiple biochemical
constraints, and in their +400 million year existence have never ventured
into fully freshwater habitats.[5]
<https://en.wikipedia.org/wiki/Cephalopod#cite_note-5>"  The groups that
have not made it into freshwater have also not made it onto land.

Cheers,  Doug

On Wed, Dec 12, 2018 at 4:17 AM Nadia Jogee via Coral-List <
coral-list at coral.aoml.noaa.gov> wrote:

>
> Hi all,
>
> I’ve been following the ‘why is an octopus smart’ thread and has made me
> pitch to you helpful lot a question I’ve often pondered- Why aren’t there
> any freshwater cephalopods?
>
> Every other group of mollusc have evolved both salty and fresh forms, yet
> not the cephalopod. This question isn’t for any other reason other than
> curiosity and wondered if anyone has any ideas!
>
> Nadia
>
>
> Sent from my iPhone
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-- 
Douglas Fenner
Ocean Associates, Inc. Contractor
NOAA Fisheries Service
Pacific Islands Regional Office
Honolulu
and:
Consultant
PO Box 7390
Pago Pago, American Samoa 96799  USA

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