aren't astrea cold water snails? It was always my understanding that they had abbreviated life spans in reef aquariums.

Trochus - awesome snail eats lots of different algae types, mine tend to stay on my rocks.
Turbos - great film grazers
Nassarius - great detrivores that also stir your sandbed
Strombus - good sand bed, stay small, good for cleaning tight areas.
cerith - nocturnal, breed well in tank and provide hermit homes, clean your glass at night, dissapear for the most part in the day.

thats a great group of snails and I wouldn't put astrea on it. (but that's just me. )