Protaster

[michele 1937]

Interesting ?
Protaster sp.
Ordovician Morocco
bought in Tucson in 2018

[ynot]

Very nice one.

[Tidgy's Dad]

Looks a pretty good specimen to me! 

Nice acquisition. 

[oilshale]

42 minutes ago, Tidgy's Dad said:

Looks a pretty good specimen to me! 

Nice acquisition. 

Great specimen with 6 arms - congrats!

[Tidgy's Dad]

4 minutes ago, oilshale said:

Great specimen with 6 arms - congrats!

Indeed. 

The rest of it looks real to me, so why on Earth did they add the 6th arm?

As Michele said, it's interesting, and a nice example of this kind of thing. 

[oilshale]

Now and then starfish with 6 arms are found. This Furcaster from the Devonian of Bundenbach also has 6 arms:

 

I think the sixth arm is real.

[Tidgy's Dad]

Yes, sometimes modern starfish have 6 arms, too. 

But I'm not sure about the arm that is top right. 

It doesn't seem to have the same detail as the others, I would like to see a closer piccie, but it seems like it may have been added to fill a space. 

Edit : Actually, looking at an enlarged image, you are right, it does look real.

[Plantguy]

Nice addition!

Regards, Chris 

[siteseer]

On 8/31/2018 at 4:04 PM, Tidgy's Dad said:

Yes, sometimes modern starfish have 6 arms, too. 

But I'm not sure about the arm that is top right. 

It doesn't seem to have the same detail as the others, I would like to see a closer piccie, but it seems like it may have been added to fill a space. 

Edit : Actually, looking at an enlarged image, you are right, it does look real.

 

Yes, I think it's real too.  The other possibility would be that there is another starfish beneath it with that arm the only part showing on the surface.

 

Could it be the same gene that gives the occasional human a sixth finger?

 

[Tidgy's Dad]

5 hours ago, siteseer said:

 

Yes, I think it's real too.  The other possibility would be that there is another starfish beneath it with that arm the only part showing on the surface.

 

Could it be the same gene that gives the occasional human a sixth finger?

 

Well, the chordates and echinoderms belong to the same superphylum, we are both deuterostomes, so we have some genetic similarities. We have 5 fingers and toes, 5 lobes in our lungs etc. Some think chordates may have evolved from echinoderms, though this is out of favour at the moment. 

My dad had six fingers. 

[Johannes]

8 minutes ago, Tidgy's Dad said:

Well, the chordates and echinoderms belong to the same superphylum, we are both deuterostomes, so we have some genetic similarities. We have 5 fingers and toes, 5 lobes in our lungs etc. Some think chordates may have evolved from echinoderms, though this is out of favour at the moment. 

My dad had six fingers. 

 

Echinoderms and chordates have completely different body symmetries. The "5-Rule" evolves in both groups at different times in the palaeozoic. Before these evolutionary events there were echinoderms with >5-radial-symmetry and chordates (bliateral symmerty with left-right-anomaly) with more than "5-fingers". (remembering: graptolites are some of our nearest invertebrate cousins... )

[Tidgy's Dad]

2 hours ago, Johannes said:

 

Echinoderms and chordates have completely different body symmetries. The "5-Rule" evolves in both groups at different times in the palaeozoic. Before these evolutionary events there were echinoderms with >5-radial-symmetry and chordates (bliateral symmerty with left-right-anomaly) with more than "5-fingers". (remembering: graptolites are some of our nearest invertebrate cousins... )

I was being funny.

And I'm quite aware of the hemichordates. 

But these three groups do appear to share a closer common ancestor and are more closely related to each other than to other phyla. 

[doushantuo]

E.g. Soluta and Cincta are not pentaradial.

At some point in the future i might start reading:

 

 

 

 

From David/Mooi(evoDevo) on HOX genes and deuterostome phylogeny

 

 

[michele 1937]

I'm glad I opened a discussion.
And interested

[fifbrindacier]

Nice piece Michele, and an interesting discussion.