Chitons, Amphineura and Polyplacophora
Ischnochiton australis, various sizes, under rock, Long Reef, Sydney, NSW, Australia. 21 December 1995. Photo: Bill Rudman
Chitons are a small class of marine molluscs, characterised by their possession of 8 dorsal shell plates usually held in place by a leathery girdle. They are bilaterally symmetrical and are usually found on hard intertidal or shallow water surfaces. In some groups however, the shell plates become reduced in size, and are often embedded in the girdle which becomes more fleshy and in some cases brightly coloured. Chitons are grazing herbivores, found in all parts of the world. They range in size from the huge Californian Cryptochiton stelleri, which grows to 300mm in length, to some that never grow more than a few millimeters in length.
I have included a page on chitons in the Forum,, because as the message below, illustrates, some chitons do look surprisingly slug-like.Authorship details
Rudman, W.B., 2002 (November 24) Chitons, Amphineura and Polyplacophora. [In] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/chitons
March 3, 2010
From: Brandon Buys
I found this in my marine tank, it has Kenyan Live Rock in
Length: 5 cm. Photographer: Brandon Buys.
firstname.lastname@example.orgBuys, B, 2010 (Mar 3) Strange thing in my tank. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/23289
This is a chiton. See the Fact Sheet and attached messages for more information. It should do no harm in your aquarium and my be useful in keeping the glass clean
November 13, 2009
From: John Markby
Hi there , i am on talking reef forum and it was suggested i ask you as no one knows for sure what this is but the best bet is some type of nudibranch...
mainly i am curious in is if it eats algae or corals or what ? as it is in my home salt water aquarium ... only recently i noticed it its probably been in there about 3 weeks and recently has started moving around alot .. moves alot at night time ....
i appreciate any time spent on this thankyou very much
2 photos enclosed are on at night time (fully stretched out - about 18 cm long at full stretch )
and day time .. it sorta hides in the rock
email@example.comMarkby, J., 2009 (Nov 13) A slug-like chiton. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/22778
This is one of a major group of molluscs called the Chitons. In most species their 8 calcareous plates are large and external forming a flexible shield - like that of an armadillo - over the body. In some species the shell plates have become reduced in size and partly enveloped by the leathery skin in which they are attached. These do appear somewhat sluglike. There are other messages on the Forum of this animal being found in aquaria [see message #8502]. I guess this tropical species, which is often found in the crevices of coral rock, is caught up in the 'live rock' trade.
Most chitons are herbivorous, so I suspect it will be a useful cleaning agent in your aquarium.
December 18, 2006
From: John Albers-Mead
I found this mystery creature on a very low tide at the Fitzgerald Marine Reserve in Moss Beach where I'm a volunteer naturalist. At first I thought it was a small sea lemon but when I looked closer it was missing a few important nudibranch details - namely rhinophores and gills.
Locality: Fitzgerald Marine Reserve, Moss Beach, exposed, California, USA, Pacific, 04 December 2006, Intertidal. Length: 1.5 inches. Photographer: John Albers-Mead.
It was probably an inch and a half long and was very rough and gritty feeling on its back. The foot had a strong grip and it immediately stuck to my finger when I examined it. We have gum boot chitons here so I was thinking this might be a juvenile but I'm not sure. Any help with an id would be appreciated.
firstname.lastname@example.orgAlbers-Mead, J., 2006 (Dec 18) Dorid-like chiton from Moss Beach, California. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/18960
Wow, if I could have a quarter for everytime I have been to Moss Beach, I'd be a rich man. I am fairly sure your critter is a Gumboot, or Giant chiton, Cryptochiton stelleri, as you suggest. Usually the texture of juvenile gumboot's is more warty than the adults, as your photo shows here. I have been sent these several times by collectors thinking it was some sort of dorid. First things I note are no rhinophoral sheaths, and no dorsal gill
Thanks for sharing this,
July 8, 2006
From: Chris Fourness
I have recently received a piece of live rock from a friend and from time to time what appears to be a slug comes out of a hole and looks to be eating algae. Today it came out rather far, it is at least 2"-3" long, 1/2" to 3/4" wide. Tan to light brown with darker markings as it creeps out of it hole. It also has circular discs on it's back. Not evenly spaced or sized or colored. They appear to be imbedded into it's body.
Can anybody tell me what this might be and or where I can go online to find it for identification???
email@example.comFourness, C., 2006 (Jul 8) Some type of sea slug?. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/17052
At a guess I would say you have a chiton - a mollusc, but not a slug. Have a look at the Fact Sheet.
March 15, 2006
From: Dawn Ahomed
Concerning message #16073:
Thanks so much for putting a name to a face (so to speak)! This query has been on my mind constantly for days, and it is a great relief to be at ease, and categorize/name my vacation photos!
p.s Yes! it does have a strikingly resemblance to Sydney Opera House! I wonder where Architect Jorn Utzon got his inspiration from, Hmmm?
firstname.lastname@example.orgAhomed, D., 2006 (Mar 15) Re: Sluglike shelled creature from South Africa. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/16114
The official view is that Utzon's inspiration was the spinnaker sail of yachts - but we know better.
March 13, 2006
From: D. Ahomed
While on vacation in Capetown, South Africa, I came across this Slug-like shelled sea creature. Can anyone tell me what is is?
Locality: Kalk Bay Beach, 1 ft., Capetown, South Africa, Indian Ocean, December 2005, rocky area of beach water, no sand near. Length: 8". Photographer: Dawn.
email@example.comAhomed, D., 2006 (Mar 13) Sluglike shelled creature from South Africa. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/16073
Living in Sydney I would say it looks like our Opera House from a funny angle. However the southern tip of South Africa is famous for the large variety of chitons that are found there. Chitons are a special group of molluscs [snails, clams, octopus etc] which have 8 shell plates, usually held together by a leathery strap or girdle which you can see in your photo.
January 14, 2004
From: Jess Trueman
My sister and I found this sea animal (two, actually) washed up on the shore of Vancouver Island, Campbell River, BC Canada. A local fisherman identified it as sea slug; he called it a Kyton. I cannot find any such animal by this name, and I am not even sure if it really is a sea slug. I was unable to find anything very similar posted on your wonderful website.
We would appreciate finding out what this creature is, if possible.
firstname.lastname@example.orgTrueman, J., 2004 (Jan 14) Unidentified Canadian Sea Slug?. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/11792
Have a look at Julie's message of the same animal from across the border in Washington State. I guess the reason you couldn't find any information is that it is spelt chiton not Kyton. If you look at the information on this page you will see that chitons have 8 shell plates on their back, some of which can be seen in your photo
January 9, 2004
From: Manuel Marquez
I have noticed a very weird Slug on my live rock, the rock could be from north West Australia. The slug moves in a very slow motion about 10mm per hour, it is heavy and very flat. Here is the pic.
Are you able to tell me what he is and what he eats. Is he OK in a smal reef tank.
email@example.comMarquez, M., 2004 (Jan 9) Slug? on live rock. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/11799
Your 'slug' isn't a slug. It is a chiton. Have a look at the chiton Fact Sheet for some background information. Chitons are a distinct group [Class] of molluscs which have 8 shell plates which form a protective 'coat of armour' over the body - much like in an armadillo. You can see some of the shell plates in your photo. A chiton or two in an aquarium can do no harm and probably is a useful way to scrape algal film off the glass
November 14, 2003
I was walking on the beach at Fort Warden State Park, in Port Townsend, Washington, USA. and came across lots of these ........ any idea what they are ?
firstname.lastname@example.orgJulie, 2003 (Nov 14) Mystery from Washington State, USA. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/11359
I am pretty sure they are chitons. Usually they don't look like slugs because they have 8 shell plates on their back but in this species the shells are hidden by layer of leathery skin. The regular bumps or ridges in your upper photo show where the shell plates are. This species is known as the Gumboot Chiton [Cryptochiton stelleri] and is also called Giant Pacific Chiton, Giant Red Chiton, Moccasin Chiton. It is the largest chiton in the world and can be found from Alaska to Channel Islands. It grows to more than 30cm long [12 inches].
January 29, 2003
From: Frans Slieker
The animal in question is not a member of the Acanthochitonidae but, as Bill suggested, is indeed a Cryptoplax: Cryptoplax striata (Lamarck, 1819) to be exact. Usually only the last four of its valves are spaced. You'll find an example of a live specimen on my chiton page: http://home.kabelfoon.nl/~fjas/livingpolyplacophora.htm
Hope I helped you out.
Rotterdam Museum of Natural History
January 15, 2003
From: Anders Olausson
I have this unidentified thing in my tank.
It´s about 8-10cm and very fast moving. It´s doesn't appear to like lights, as soon as the lights go on the slug (or what it is) disappears.
Pleas help me to identify.
email@example.comOlausson, A., 2003 (Jan 15) Alien in my tank. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/8852
November 27, 2002
From: Dee Ryden
Dear Dr. Rudman,
I have enjoyed your site very much and have learned a great deal, the amount of information is amazing! I was hoping that you could help me out with an identification problem I'm having with a former tank
Here's what I know about him from my observations. He seemed to be primarily a nocturnal creature who was very peaceful with the rest of the tank mates. Save for the purple coraline algae. Which was what prompted me to remove him, he nibbled incessantly on the coral. His texture is that of a super tough muscle, very firm but not hard like a shell. He had little pointy things around the top portion of his body and these three colourful circles that seemed like some kind of plates. The top 1/4 of him was all I had ever seen until his removal and I was surprised that the rest of his body didn't have those similar colourful plates. His underside was like that of a snail, one big long foot and a mouth at one end. From all the searching I have done on the web, the closest I could come to was Acanthochitona hirundiformis. But he still didn't look like that completely. Is he a Chiton? if so which one? or who is he? Most Chitons seemed to be much more circular and uniformed with the plates on their body. Well from what I could tell any way. :) I now noticed that I have another one, but it seems to be a juvenile, just barely a half an inch. Still a nibbler though! I really hope you can help me out cuz this has been driving me crazy! So any information you can give me would be most appreciated!
Thank you for your time Dr. Rudman.
firstname.lastname@example.orgDee Ryden, 2002 (Nov 27) Chiton or slug?. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/8502
Your animal is indeed a chiton. Most chitons have 8 very noticeable shell plates, but in a number of families there is a tendency to either reduce the size of the plates, or to hide much of each plate in the skin. it is not just snails that have tried so many times to become slugs. If you look at your photo there are 8 plates, but the ones on the right (posterior end) are considerably separated from one another. I'm afraid I'm not a chiton expert so I won't attempt to name your animal. It could be an acanthochitonid, as you suggest, but it looks very like a species of Cryptoplax to me. Whatever its name, I'm sure it won't do much damage in your aquarium.
December 11, 1998
From: Rebecca Johnson
Dear JM and Dr. Rudman,
Concerning JM's Dec 1st message: I think the large molluscs JM has found on the beach in Monterey, CA are chitons. From his description they sound like dead Cryptochiton stelleri. This is the largest chiton in the world. It has internal valves and a hard, rough, reddish brown mantle. I have seen them washed up on the beach many times and they look a bit like American footballs. I could not find a web site with a picture of the live animal, but maybe someone else can. I hope this helps.
email@example.comJohnson, R., 1998 (Dec 11) Re: A Californian mystery. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/373
It's a pity anything dead and dishevelled gets called a "slug". Certainly a Cryptochiton would fit the bill. I didn't realise they got so large in your part of the world .. but I guess it is California!
December 11, 1998
From: Peter Firminger
Re Rebecca's message. I had a bit of a search and came up with a few sites..
The first picture does look like Rebecca's description of a red gridiron football. .. Bill Rudman.
December 1, 1998
November 28th, 1998
30 miles South of Monterey Bay on the Pacific Coast of Northern California
SEEN: 2 large (size of adult hand), bean shaped, mollusks(?)/nudibranchs(?) They had the coloration of a cranberry bean, (striped brilliant red) and the very general outline of a snail. There was no shell! They were beached after a winter storm amidst many tons of giant kelp that had been torn up and washed ashore.
On their ventral (?) surface was a dark, black strip resembling the rand of a hiking shoe - their feet?. At their "heads" were perhaps 2 sets of antennae.
Any ideas what I saw?? I'm very curious but no time to research and my library is all in boxes.
Perhaps someone from California knows what JM is describing ... Bill Rudman