Black leech looking things in my tank

[chickers]

I have had my 33 gallon tank up and running for about six months. A few months ago we noticed a black leech looking creature crawling around and decided to leave it to see what happened. Now we have about 3 big ones and 10-12 little ones. Don't know where they came from other than the live rock that we used to start our tank but now over the last few weeks we have hardly any algae left on the glass or rocks of our tank. These things have a tiny white dot on their backs but are all black otherwise. Should we leave them alone or cull them or get rid of them all if we can. I am worried that there won't be enough food for them and my snails. Any advice would be greatly appreciated.
Thanks
Cheri

 

[steve-s]

Sounds like either a keyhole limpet or elephant snail. My guess is elephant snail by this part alone....

These things have a tiny white dot on their backs but are all black otherwise.

http://www.seaslugforum.net/factsheet.cfm?base=scutus

Cheers
Steve

 

[Fluff]

Sure does sound like the elephant snail. I agree with steve, a pic though would help to confirm the ID.