Lori,

Books have been & can be written to answer those questions....

Molluscs first appeared more than 550 million years ago. But I am probably
wrong on that & somebody will correct me.

The question of what they descended from has still not been answered & being a
historical question, may never be answered satisfactorily. Some marine
molluscs have what is known as a trochophore larva, which is also present in
some marine annelids, sipunculans and echiurans, suggesting that these four
phyla shared an ancestor at some point, which was probably a worm-like
creature.

I believe marine gastropods & chitons came first, then the others. Of course,
within each class different families, genera, or species may have appeared at
different times. For example, the pulmonate land snails as a taxon evolved
after the marine gastropods.

>What descended from molluscs?

No extant phylum seems to have descended directly from another extant phylum.
So, nothing descended from molluscs. This generalization applies to lower taxa
as well. Because, most species are continuously evolving, one can't usually
say that a given extant species descended directly from another extant
species. To take a familiar example, Homo sapiens didn't evolve from any known
species of living ape or monkey. But rather, the humans & the apes had a
common ancestor at some point.

Hope this helps.

A.


On Mon Jan 03 21:06:27 2000,
"Lori Schroeder" <[log in to unmask]> wrote:
>Dear Conch-l,
>
>I was wondering... what the current thought is as to when molluscs first
>appeared in history?  What did molluscs descend from?  What order did
>molluscs appear?  What descended from molluscs?
>
>My father asked me the first question recently during a meal we were
>sharing.  I couldn't answer his question and spent a few days pondering
>with no resolution.
>
>Thanks,
>
>Lori Schroeder
>[log in to unmask]
>