I haven't a clue, but always an opinion!  I would bet octopus and squid do
not have optical sensors in their skin as they have very advanced eyes and
most likely use their eyes for this purpose.  On the other hand, nerites
have "closed eyes" that probably do not see much more than light and dark
shapes.  These combined with their other senses, including the optically
sensitive dark areas on their skin, still leaves them far short of the
visual acuity of cephalopods.  The difference here is a group of mollusks
(octopus and squids) that are active hunters with great mobility.  On the
other hand you have the neritids who are heavily armored grazers that depend
upon a number of defensive mechanisms that all added up pretty much equal
"hunker down."  No need for great visual acuity there.

Tom E

> -----Original Message-----
> From: Conchologists of America List [mailto:[log in to unmask]]On
> Behalf Of Mountain Blue Designs
> Sent: Friday, May 09, 2003 4:54 PM
> To: [log in to unmask]
> Subject: Re: eyes
>
>
> Is this the same way of seeing that octopus and squid sense colour and
> respond with changing their own  colour?
>
> -----Original Message-----
> From: Conchologists of America List [mailto:[log in to unmask]]On
> Behalf Of Thomas E. Eichhorst
> Sent: Saturday, 10 May 2003 3:41 AM
> To: [log in to unmask]
> Subject: Re: eyes
>
>
> Art -
>
> Can't say much about all mollusks, but I can say that some
> gastropods "see"
> through their skin.  Tests on Nerita picea Recluz, 1841 (an Hawaiian and
> Johnson Island endemic nerite) demonstrated a response to shadows
> generated
> by dark pigmented areas on the dorsal portion of the foot of the animal.
> These are usually longitudinal, irregular, dark stripes and are found in
> quite a few gastropods.  In other words, even though the animal
> has two eyes
> (which also react to shadows) it also sees with its skin!  The same dermal
> shadow response has been recorded in Nassarius reticulata (Linnaeus, 1758)
> and the garden slug Arion ater.
>
> Tom E.