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Chitons live worldwide, from cold waters through to the tropics. They live on hard surfaces, such as on or under rocks, or in rock crevices.
Some species live quite high in the [[intertidal zone]] and are exposed to the air and light for long periods. Most species inhabit intertidal or subtidal zones, and do not extend beyond the [[photic zone]], but a few species live in deep water, as deep as {{cvt|6000|m|ft}}.<ref>{{cite journal |last1=Lindberg |first1=David R. |title=Monoplacophorans and the Origin and Relationships of Mollusks |journal=Evolution: Education and Outreach |date=1 June 2009 |volume=2 |issue=2 |pages=191–203 |doi=10.1007/s12052-009-0125-4 |s2cid=26108547 |url=https://link.springer.com/article/10.1007/s12052-009-0125-4 |access-date=19 April 2022 |language=en |issn=1936-6434}}</ref>
Chitons are exclusively and fully marine, in contrast to the [[Bivalvia|bivalves]], which were able to adapt to [[brackish water]] and fresh water, and the [[Gastropoda|gastropods]] which were able to make successful transitions to freshwater and terrestrial environments.
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Although chitons lack [[osphradium|osphradia]], [[statocyst]]s, and other sensory organs common to other molluscs, they do have numerous tactile nerve endings, especially on the girdle and within the mantle cavity.
The order Lepidopleurida also have a pigmented sensory organ called the Schwabe organ.<ref>{{Cite journal |pmc=3916795 |year=2014 |last1=Sigwart |first1=J. D. |title=A new sensory organ in primitive molluscs (Polyplacophora: Lepidopleurida), and its context in the nervous system of chitons |journal=Frontiers in Zoology |volume=11 |issue=1 |pages=7 |last2=Sumner-Rooney |first2=L. H. |last3=Schwabe |first3=E. |last4=Heß |first4=M. |last5=Brennan |first5=G. P. |last6=Schrödl |first6=M. |pmid=24447393 |doi=10.1186/1742-9994-11-7}}</ref> Its function remains largely unknown, and has been suggested to be related to that of a larval eye.<ref name="sumner2015">{{cite journal | title = Is the Schwabe Organ a Retained Larval Eye? Anatomical and Behavioural Studies of a Novel Sense Organ in Adult ''Leptochiton asellus'' (Mollusca, Polyplacophora) Indicate Links to Larval Photoreceptors | last1 = Sumner-Rooney | first1 = L.H. | last2 = Sigwart | first2 = J.D. | journal = PLOS ONE | date = 2015 | doi = 10.1371/journal.pone.0137119 | volume = 10 | number = 9 | page = e0137119| pmid = 26366861 | pmc = 4569177 | bibcode = 2015PLoSO..1037119S | doi-access = free }}</ref>
However, chitons lack a cerebral ganglion.<ref>(Thorne. J. M, 1968; Moroz. L, et al., 1993).</ref>
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Chitons are generally herbivorous grazers, though some are omnivorous and some carnivorous.<ref>{{Cite journal |doi=10.1080/00852988.1984.10673963 |title=Distribution and feeding of chitons in a boulder habitat at West Island, South Australia |journal=Journal of the Malacological Society of Australia |volume=6 |issue=3–4 |pages=101–111 |year=1984 |last1=Kangas |first1=Mervi |last2=Shepherd |first2=S.A.}}</ref><ref>Barnawell, E. B. (1960). The carnivorous habit among the Polyplacophora</ref> They eat [[alga]]e, [[bryozoan]]s, [[diatom]]s, [[barnacle]]s, and sometimes [[bacteria]] by scraping the rocky substrate with their well-developed [[radula]]e.
A few species of chitons are [[predatory]], such as the small western [[Pacific]] species ''[[Placiphorella velata]]''. These predatory chitons have enlarged anterior girdles. They catch other small [[invertebrate]]s, such as [[shrimp]] and possibly even small fish, by holding the enlarged, hood-like front end of the girdle up off the surface, and then clamping down on unsuspecting, shelter-seeking prey.<ref>{{Cite web |url=https://www.youtube.com/watch?v=aCLO7sOexYk |title=
<!--repeat Some chitons exhibit homing behavior, returning to the same spot for the daylight hours and roaming around at night to feed.-->
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