Martin,

Check some of the reef aquarium sites.  I don't know if you will get an 
exact identification, but these little stars are common in reef 
aquaria.  They typically have 6 or 7 arms and generally stay very small, 
no larger than what you see now.  They probably do no harm but if they 
start to get too numerous you can remove them manually.  There are 
probably more than you see hiding in the live rock and sand.

Rich Pierce

On 8/22/2014 10:56 PM, Martin Eastburn wrote:
> This is a bit out of my realm (Physics, Mathematics) and dabble in sea 
> shells.
>
> We have a 300 liter salt water tank with 'live' sand.   What came in 
> the sand were
> some shells - live and algae eaters at that!  Yea.   Snails tend to 
> over propagate themselves.
>
> I also have, and thus my question, some starfish.  These are pinky 
> finger nail size or smaller.
> They are also 7 legged and gray.
> I normally see only 5 legs and Sun (many) legs in books and the web.
>
> Where in the web world is a good site that might help in Identifying 
> these wall walkers ?
> We have 11 in the tank, for now the number is a who cares.  If they 
> grow hand size, they will
> be a problem.  I hope to grow them and find new homes.  Knowledge is 
> the best friend at this
> time.
>
> Martin
>
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