6 Point Starfish

[kelley_mc]

Hello Everyone,

I was looking at my fishless QT tank where my chaeto is living temporarily and noticed a small starfish on the glass. The strange thing was he had 6 points, not the typical 5. How abnormal is this? I know that starfish will regenerate a leg if one falls off. Could this have something to do with it?

Kelley

 

[rosshind]

Starfish are echinoderms, and like all echinoderms, they have pentamarous symetry.. This means they can be divided into five, and each fifth will be around about the same shape as each other fifth. In the case of the average star fish, this pentamarous symetry is easy to see. That said, it is possible to have ten arms, and still maintain pentamarous symetry.

Hmm... a 6 armend sea star.... The first question to ask is... Did it have 5 arms to begin with, or did it have more? Do you know the species? It sounds like a massively rare occurance to me, about as rare, one would expect as a human having, say three arms and three legs instead of two, thus giving them trilateral symetry, rather than the bilateral symetry everyone I've seen enjoys.

 

[Amphiprion]

Not as uncommon as you might think, especially in starfish that reproduce by fission, such as Asterina spp., which is what I suspect kelley_mc's to be.

 

[greenbean36191]

It's not rare at all. Lots of species regularly have numbers that differ from the typical 5-part symmetry. Pentamarous symmetry is just the ancestral form. Lots of species, like crown of thorns and sun stars have evolved more derived forms. There are also lots of cases where some members of normally 5-legged species occasionally develop with 6 or 7 legs, which isn't rare either. Many species also normally have 6 legs, especially with species that reproduce by fission.

If I had to guess what star you're seeing, it's probably Asterina, which can have anywhere between 3 and 10 legs.

 

[kelley_mc]

I guess I don't have something that rare then. Is does look something like this:

 

[dippin61]

i have asterinas with 7-9 arms.

not really uncommon in this species.

 

[rosshind]

Hmm.. ok.

I guess I need to write to my old uni and get my money back. Thanks for clearing that up guys