i have a 55gallon that is heavily stocked and fairly heavly feed - mixed reef...
and I have something like the following in it
5-10 tonga nassirius snails - in sand bed
10 narssisuris vibex ( they are really tiny) in sand bed
10 cerith sand bed during the day glass and rocks at night
and my fav fav fav snail - the Queen Conch
5-8 mexican hermits ( also called red legged)
2 cleaner shrimp
1 tuxedo urchin
1 nano serpant star
those are rough numbers I have added snails a few times since I started the tank for diversity and to account for mia or deaths. BUt I have added these over the last 18 months
I started with the vibex, astrea and hermits.