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Tiny snails between zoa polyps


Supporting Member
Sep 29, 2017
I was about to frag as I went that when I saw some tiny snails between the polyps. About 5 snails and a micro brittle starfish to be exact. The zoa colony seems to be doing fine though there is some missing flesh between a couple polyps.

Are these sundial snails or something else?
Do micro brittle stars eat zoas?
20190313_193829.jpg 20190313_193348.jpg



Board Member
Jun 24, 2009
I think those are Collonista snails.


Ronald L. Shimeck PHD - from the above linked article said:
Collonista [Link 1, 2] (Figure 10)

Collonista are "mini-Turbo snails." They are seldom purchased by hobbyists, but are relatively common in reef tanks anyway, because they appear to hitchhike in on live rock or in some live sand. When hobbyists first see them, they presume them to be "baby" grazers of some sort. Instead, they have some of these animals. They reach a maximum adult size of about 1/4th inch (6 mm) in height and diameter. They are often tan to white and have mottled brown color patterns on the shell. They can be distinguished from all other Trochoideans by their small size and the presence of a small pit or hole in the center of the calcareous operculum that plugs the aperture. They reproduce well in aquaria, and are quite good grazers. If present in large numbers, they may effectively replace all other grazers in our systems.

Figure 10. Collonista. These small Trochoideans are distinguished by their minute size and
by the small pit in the center of their operculum.​