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Re: Time Line



On Sep 7, 17:08, Stan Friesen wrote:
} Subject: Re: Time Line

>  > > First rudists
> 
> An early group of corals, rather different than the living hexacorals.

Um, no.  The rudists were reef-building mollusks (clams).  Not corals at
all, but a similar niche (reef-builder).

>  > > First grazing echinoids
> 
> Echinoids are starfish, sea-lilies, sea-cucumbers, sea-urchins
> and so on.  The earliest ones were rather like sea-lilies, and
> probably were what is known as filter feeders (a "passive" sort
> of feeding).  Later forms, including most living forms, use a
> more active form of feeding, involving searching for food - that
> is the "grazing" forms and the even more derived carnivorous
> forms, such as starfish.
> 
> [Ack, or are echinoids a *sub*group of the echinoiderms??].

Yes, the echinoids are a subgroup of the echinoderms.

The echinoids are sea urchins and sand dollars.  Echinoderms, but only a
sub-group thereof.  Starfish, sea lilies (crinoids), sea cucumbers, etc.,
are all echinoderms, but not echinoids.

I suspect you're right that echinoderms were meant originally, though.
"First grazing echinoderms" seems to make more sense than "first grazing
echinoids".   


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Bob Myers                               Unocal Information Systems Support
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