ChrisMcA's picture


Observed: 28th August 2007 By: ChrisMcAChrisMcA is knowledgeable about InvertebratesChrisMcA’s earned reputation in InvertebratesChrisMcA’s earned reputation in InvertebratesChrisMcA’s earned reputation in InvertebratesChrisMcA’s earned reputation in Invertebrates

Several of,under a boulder. Look like red seaweed so easily missed

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Joe Botting's picture


Certainly looks like Antedon to me. It is indeed a crinoid, albeit a stemless one, but although they're quite an ancient group of echinoderms, they're not the ancestors of the others. In fact, the oldest known fossil starfsh appeared at about the same time (early Ordovician), with the other groups appearing not much later. Echinoderms have a large number of long-extinct classes, some of them utterly bizarre (look up helicoplacoids or stylophorans), and it's still unclear what the ancestral form was. Most bets are on a group called the edrioasteroids, though, which are just as weird as the others. A wonderful phylum, echinoderms...

ChrisMcA's picture

Thanks Joe for your

Thanks Joe for your correction & info.
The 'theory' I had (an old theory or a misconception?) had the crinoids as ancestral with their 10-fold symmetry, etc,(but no sign of this on the net!).
But I did find a paper said crinoids are the "most ancient class of living echinoderms" (citing Smith 1977), which, of course, isn't the same thing. Also to my surprise, another saying crinoids can have from 5 to 200 arms (but start with just a few).

Joe Botting's picture

You're welcome

When it comes to evolutionary origins, you'll find a lot of relatively old ideas still being cited. There's a lot of recent data coming from genetics, which has largely clarified the basic relationships of echinoderms, but the fossils are still difficult at the critical times - although they are turning up, the skeletons of these things disarticulated so easily that a complete fossil is quite a rare find...

There certainly are some amazingly disparate fossil crinoids - everything from microcrinoids with five tiny arms, to Carboniferous giants with stems allegedly 30 m long. The ones we have left are a pretty limited remnant of a once very-diverse class. But they're still amazing little animals, and I'm envious of you for finding these!

ChrisMcA's picture

I didn't recognize them at

I didn't recognize them at the time,but a few days on found 1 attached to a tiny bit of weed & so could photo it swimming,at