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Margarita Snail- Margarites pupillus
http://www.aquariumadvice.com/articles/articles/56/1/Margarita-Snail--Margarites-pupillus/Page1.html
Fluff
Stay at home mom, been keeping fish tanks for as long as I can remember. Been doing sw tanks since 2003.  
By Fluff
Published on 01/13/2008
 

These snails are often sold as algae grazers for the reef tank. Unfortunately, although they are awesome algae grazers, they are not the best choice for most systems


This article was contributed by Aqarium Advice member fluff

Common Names: Margarita snail, Pearl snail
Family: Trochacea
Origin: Eastern Pacific
Main Ecosystem: Deep, cooler waters
Salinity: Marine
Temperament: Peaceful
Diet: Herbivore
Care: Listed as easy
ph: 8.0-8.4
Temperature: 72-78
Potential size: 1"
Water Region: substrate, rocks
Activity: Nocturnal
Lifespan: Unfortunately, not long lived.
Color: pearly gray
Mouth: Normal
Acclimation: slow drip acclimation
Breeding: doesn’t breed in captivity

Comments: These snails are often sold as algae grazers for the reef tank. Unfortunately, although they are awesome algae grazers, they are not the best choice for our systems. These snails are found in deep cool water (39 degrees or lower) and the warm water of our tanks shorten their lives significantly. Even with the high mortality rates, they continue to sell them. There are much better choices and these snails IMO should not be sold.

Sources:  http://www.liveaquaria.com Reefkeeping magazine