>In short: if we accept "species" pairs with a different mode of
>larval development as true, biological species, then we have to
>accept the very difference in larval development/dispersal
>strategy (and in the resulting, visible differences in protoconch
>characters) as specific characters  by definition. And of
>course, then poecilogony no longer has any meaning. Instead, the
>switch in mode development by definition IS the starting points for
>new species: one species cannot have two modes of larval development
>because then there ARE two species!
>This has an interesting, if not exciting consequence because the
>origin of new species then does not take thousands or millions of
>years (which is true for allopatric speciation), but just one
>generation. If not a split second. It also explains why marine
>gastropods are so succesful if success is measured by number of
>species: many of them have a built-in mechanism to create new
>species (initially differing only in mode of larval development but
>sooner or later also in size, colour, ornamentation, etc).
>The real question that ought to be answered is not whether or not
>poecilogony excists (it does not by definition), but what causes the
>shift in larval development (how does a species, or in fact
>specimen "KNOW" why to change larval development/mode of dispersal?
>Are environmental factors responsible? And if so, which?), and
>why should it be irreversable from planktotrophic to "direct"
>devolopment (if that is true at all).

This sounds like the "sinistral and dextral specimens must be
different species"... or even subgenera... argument.

If you take eggs from ONE capsule and hatch them under differing
environmental conditions, and the larvae develop different types of
protoconchs, what conclusion do you come to? That the single capsule
contains eggs of more than one species?
--
Andrew Grebneff
Dunedin, New Zealand
64 (3) 473-8863
<[log in to unmask]>
Fossil preparator
Seashell, Macintosh & VW/Toyota van nut
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I want your sinistral gastropods!
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Q: Because it reverses the logical flow of conversation.
A: Why is top posting frowned upon?