Is it true that if you cut a starfish's arm off it will grow back? What if you cut a starfish in half?

Last edited by Alistair McGowan (23rd Apr 2007 12:00:29)

Hi Carly,
Yes it's true, and it is one of the most intriguing things about starfish.  This is because Starfish are in the large group (Phylum) of animals called echinoderms, which is the closest related group of animals to our Phylum, the chordates.  However, if you cut off anything more than your fingernails it does not grow back.  Why this is the case for starfish, but not humans, gerbils, dogs, cats, rabbits etc. is the interest of much study by developmental biologists.
The main thing that seems to be important is that there is enough of the central disk of the starfish intact, for the animal to grow from.  This does not need to be very much, indeed it has been reported that whole starfish have regenerated from an arm and a piece of the body.

Having said that the wonderful thing about the starfish is that it can regenerate arms (and a body) while we cannot and a list of animals that also lack this ability, you will have seen that all of these animals are mammals.  If however, we move down the vertebrate branch of the the chordate tree, we soon come to the amphibians.  The salamanders are chordates, and vertebrates.  They are even more closely related to us than starfish.  The link below is from a Canadian university site, The University of Guelph.  There researchers have been trying to understand the way that regeneration of the salamander limb occurs.

http://www.uoguelph.ca/zoology/devobio/ … egen1.html

Well, now if the salamander can do it, and it is an evolutionary brother, rather than a cousin like the starfish, why are we interested in the starfish?
The answer is that Starfish are a lot easier to work with.  You can easily watch how they develop with a microscope.  There genetics is a little easier to understand as well.  They have (roughly) one quarter of the number genes that a salamander has, so we can build up a picture of what is going on at a genetic level more easily.

I hope that answers your question.

Last edited by Neil Gostling (6th Feb 2007 09:58:35)