Rule of thumb?

[paul monfils]

Hi Roger,

There is really no general rule of thumb.  It's kind of like venomous snakes - you just have to know what the dangerous ones look like.  All the really dangerous snails, those which could hurt you or kill aquarium fish (and there are only a few of them) are members of a family called Cone Shells. You can see a picture of the most dangerous cone shell species here:

<a href="http://www.manandmollusc.net/advanced_introduction/cones.html" target="_blank"><!-- m --><a class="postlink" href="http://www.manandmollusc.net/advanced_introduction/cones.html">http://www.manandmollusc.net/advanced_i ... cones.html</a><!-- m --></a>

These all live in the western to southwestern Pacific area. You are not likely to find them in mangrove habitats.  There are many other species of cone shells that are not dangerous.

In mangrove areas you can find some snails that are algae eaters, and others that feed on molluscs, worms, and other invertebrates. Also, some that are scavengers, feeding on dead fish or other dead organisms.

Probably the easiest way to identify the algae eaters is to observe them in their natural habitat.  You can identify the scavengers by throwing a piece of fish or a crushed oyster in the water and coming back a half hour later to see what is eating it.  The species that live high on the mangrove roots are most likely algae eaters.