chiton | The Marine Detective

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Ky, Ky, Ky – Chitons!

I’ve wanted to write a blog about chitons for so long because, they are wondrous and . . . we need wonder.

If you are fortunate enough to live near the Ocean, chitons are there, on rocks right in the intertidal zone, descendent from ancestors that date back ~500 million years. Chitons are in fact referenced as living fossils since their body design has not changed significantly for more than 300 million years.

Other members of this class are found at great depth. There are about 1,000 species worldwide with 50 known to live in the range from Baja California, Mexico to the Aleutian Islands, Alaska.

What makes them unique among molluscs (the soft-bodied invertebrates) is that while some molluscs have no shell (octopuses, squid and sea slugs); and some molluscs have one shell (snails, abalone and limpets); and some molluscs have two shells (clams and oysters) . . . chitons went their own way to all have EIGHT shells, known as plates.

This is reflected in the name of the class to which they belong – the “Polyplacophora” which translates into “many plates” in Greek. Oh and “chiton” also reflects that they have multiple shells. Chiton is Greek for “coat of mail”. Chiton is pronounced “ky-ton” by the way.

*Chiton anatomy – diagram retrieved from this source.*

But all the preceding information about chitons is what you could read in a field book. Let me share the wonder of chitons with you as it has awakened in me, taking my appreciation far beyond the limits of drawings and words in biology textbooks.

Chitons are THIS.

*Lined Chiton – Tonicella lineata to 5 cm long. This is also the species in the photo at the top of this blog item. There’s such diversity in the colour of this species!*

And THIS

*Believe this one is a Blue-line Chiton – Tonicella undocaerulea to 5 cm long.*

And THIS

*Woody Chiton – Mopalia lignosa to 8 cm long.*

And THIS

*Black Katy Chiton aka Black Leather Chiton – Katharina tunicata to 15 cm long.*

And THIS

Red Veiled-Chiton (Placiphorella rufa to 5 cm long) – unique amongst chitons in how it feeds.
Most chitons graze, scraping algae off rocks with their radula (see video at the end of this blog).
However, Veiled Chitons are carnivores! When an animal wanders under
their veil, this triggers the veil to drop and then . . . lunch.
You can see how quickly that happens in the video at the end of this blog.

*Veiled Chiton – Placiphorella velata to 6 cm. Soft coral is growing on top of the Chiton.*

By having eight plates and a band of muscle (the girdle) chitons are flexible and can secure themselves really well to uneven or curved surfaces. This is very different from molluscs like limpets. With their single shell, they have to be on a very flat surface to be secure, and therefore safe from predators.

In most species of chiton, you can see the eight plates. The exception is the giant in the group – the Gumboot Chiton aka the Giant Pacific Chiton. In this species, the girdle fully covers the plates.

See the photo below and my blog dedicated to Gumboot Chitons at this link. That blog includes photos of their “butterfly shells” and video of Gumboot Chitons spawning. Yes, you can then discern males from females!

Gumboot Chitons are another species in these rich waters that are the “biggest of their kind in the world”. The maximum size of Cryptochiton stelleri is reported to be 35 cm!

*The plates on the right are from a Gumboot Chiton.*

Nature once presented me with the following opportunity to take a picture that shows the diversity of molluscs. I did not move the species into the positions you see in my photo below.

**Mollusc biodiversity**
*1. Keyhole Limpet, protected by its single-shelled cap and by sucking down on flat surfaces. This individual is in a precarious position for predation because it is not secured to a flat surface.*
*2. Wrinkled Amphissa Snail, protected by its single shell and a keratinous “trapdoor” (operculum) that seals the shell.*
*3. Pomegranate Aeolid (nudibranch species), with no shell but protected by the stinging cells obtained from its prey – the Raspberry Hydroid.*
*4. Blue-Line Chiton protected by its eight shell plates and a strong band of muscle that lets it solidly adhere to non-flat surfaces.*

Sources:

Berkley Education – The Polyplacophora, Chitons, the eight-shelled molluscs
Science Direct – Polyplacophora
Shape of Life – Chiton
Sigwart JD. Morphological cladistic analysis as a model for character evaluation in primitive living Chitons. Am. Malacol. Bull. . 2009;27:95–104
Tradtional Animal Foods of Indigenous Peoples of Northern North America – Chitons

Here’s video showing the radula (rasping mouthparts) of a Gumboot Chiton.

Video of a Veiled Chiton being triggered and dropping its veil.

Gumboot Chitons Spawning!

I’m excited to share video with you of Gumboot Chitons spawning. These marine neighbours most often seem quite inanimate – having a life where they keep their undersides protected by sucking down hard on rocks but, when it’s time to mate . . . . .

Female! © Jackie Hildering

First just a little background: “Chitons” are marine molluscs (soft bodied animals) that, rather than having one of more shells to protect themselves, they have 8 armoured plates surrounded by a thick band of muscle. This allows them to suction onto surfaces very effectively since the 8-plates give such flexibility that they can even get a good grip on surfaces that are not flat.

There are many members of the the chiton class but the Gumboot Chiton (Cryptochiton steller; aka Giant Pacific Chiton) is very unique in its appearance.

It’s another “the biggest of its kind in the world” that inhabits the cold, rich waters of the northeast Pacific. It can be 35 cm long and about 2 kg. They are very slow growing and very long lived! This source reports that chitons that are 15 cm long are likely 20 years old and that they may live to be more than 25. That’s one old gumboot!

The Gumboot Chiton is also the only chiton species that has flesh completely covering the 8 plates. The texture and colour of this “girdle” offers them great camouflage and is where the “gumboot” descriptor comes from. The genus name “Cryptochiton” relates to this camouflage and that the 8 plates are hidden under the girdle. These plates are very uniquely shaped, and well-described with the name “butterfly shells”.

Smaller dead Gumboot Chiton. Image shows the thick band of muscle with which Gumboot Chitons secure themselves. Fish species is Longfin Sculpin. ©Jackie Hildering.

Small dead Gumboot Chiton. Image shows the thick band of muscle with which Gumboot Chitons secure themselves. Fish in this image is a Longfin Sculpin. ©Jackie Hildering.

Apparently some First Nations did sometimes chew on this species but I am SURE that this is not the cultural origin of some people referring to this species as “wandering meatloaf”!

I don’t know where I picked this up, but I believe that one of the First Nations’ names for gumboot chitons translates (very) loosely, into “stuck on rock with face forever”. This would be an incredibly good descriptor since most chitons stay “face” down, grazing on algae by scraping with the sharp teeth-like structures of their radula. Thereby, they don’t expose their soft bodies and reduce the chance of predation.

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I once found a Gumboot Chiton that had been dislodged by a predator at low tide. It is then that I learned that they have the ability to curl up on themselves like a pill bug!

But outside of a rare experience like this, you don’t often get a chance to see how very alive and animal-like they are.

Unless . . . they are spawning.

Then, up came the bodies of the Gumboot Chitons, into a very unique funnel-like shape. The “gonadal pores” are near the bottom end of the animals, but by positioning themselves in this shape, they channel the sex cells upward.

When spawning, you can clearly see which Gumboot Chitons are male and which are female!

It was just remarkable to see this, feeling truly as if some secret world was being revealed, and the coordinated timing of the spawning was astonishing.

Of course when you are a broadcast spawner, you need to release copious amounts of sex cells and need to do so at the same time or there will be even less chance that egg meets sperm. You can imagine how many eggs need to be fertilized if any of your zooplankton offspring are going to survive since so many animals feed on plankton.

To my knowledge, science has not concluded exactly what the cues are for “Hey fellow Gumbooot Chitons, it’s spawn time NOW!” It has to be temperature, light, tide and/or amount of food that determines the time is right.

Hum . . . seems to me that those cues may be significant between individuals of our species too!

Additional images:

Chiton plates on the right are those of the Gumboot Chiton.

Gumboot Chiton predated on by Sunflower Star

Gumboot Chiton being ingested by a Sunflower Star. Unknown if this was the result of predation or if it is scavenging i.e. that the Gumboot Chiton was already dead. ©Jackie Hildering.

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NOTE: I would normally NEVER disrupt a chiton as this would potentially damage the animal. The Gumboot Chiton in this image had been dislodged by a predator and was lying upside down. Used it as an opportunity to discuss ethics with the Sunset School students. We decided to right it and put it on a rock so that s/he could be protected again by sucking down ©Jackie Hildering.