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Saturday, June 23, 2012

Crayfish have teeth like us?

Shmuel Bentov of Ben-Gurion University and his colleagues have found that one type of freshwater crayfish (Cherax quadricarinatus) has an enamel-like coating over its molars. Right now, I’m imagining Sebastian the crab from Disney’s The Little Mermaid breaking into a toothy grin. That’s not quite what the researchers found.

In reality, crayfish look like this:

They do not have teeth that look like this:
Digital image created by Sam Fentress 7 June, 2005.

They do however have mandibles with a grinding surface that are analogous to our molars.

Teeth have a hard outer surface, a softer, more pliable center for absorbing shock and tension, and a binding layer between the two. For vertebrates such as ourselves, the outer layer is composed of calcium phosphate hydroxyapatite. Invertebrates have employed a number of minerals to harden their teeth including calcium carbonate, iron oxide and silica, but crystalline apatite has not been one of them. Apparently, C. quadricarinatus has not been keeping up with the literature because its mandibles contain fluorapatite crystals that are quite similar to the apatite crystals in our teeth.

Unlike vertebrate teeth, the crayfish mandibles are part of their exoskeleton. As such, they are shed every time the animal molts. Despite this rather significant difference in tooth maintenance, C. quadricarinatus has teeth that are quite similar to the ones found in vertebrates. This is most likely an example of convergent evolution (separate lineages converging on a single solution to a common problem, in this case, how to process food).