Fist thing to know, some are good guys & should be left in your aquarium, others are predatory and should be removed. Identifying the species of Chiton is essential to know if it is reef safe or not, but it is only a very small minority of Chitons that are predatory. You would have to be VERY unlucky to end up with a predatory species in your aquarium.
Chitons, or Sea Cradles, are often found as hitch-hikers on liverock. They look a bit like a woodlouse (Chuggy Pig), with 8 over-lapping leathery looking shells. There are over 800 identified species of Chitons.
Chitons come in various in colours, ranging from white-brown to green, yellow, purple and even red. They usually curl up into a ball when removed from the rockwork.
Some grow up to 33 cm in length but ones found in the aquarium do not usually grow larger than 1-6 cm
Tank Requirements
- These snails are reef safe
- Clean and stable water
- Stable magnesium & calcium levels
- Algae, if there is no algae in your tanks their diet can be supplemented with Nori (dried seaweed)
- They will not tolerate a high nitrate level
- Recommended stocking level is 1 – 5 snails per 20 gallons (90L) of water.
Feeding
Nearly all chitons are grazing herbivores. They scrape microscopic algae and bacteria off the rocks they are grazing. A few species of chitons are predators eating other small invertebrates, such as shrimp and possibly even small fish.
Chitons are excellent cleaners of tanks, as they will spend all day and night grazing on algae. Their various colourings and patterns’ will make an excellent addition to your clean up crew.
Chiton in a ball 
Chiton Underneath 
Brown Chiton 
Chiton Tonicella lineata 
Groupd of Chitons
Identification of Chiton Species
As mentioned earlier, there are over 800 know species of Chiton. As a result of this, I can’t sit here and write about each one!
A few good resources for you though if you want to be sure of the species:
http://www.bily.com/pnwsc/web-content/Chiton%20Identification.html
http://emeralddiving.com/id_chitons.html
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