The pelagic veliger stage is an advantage to a species if
it can produce more viable offspring by broadcasting its
young over a wide area than it would by laying eggs from
which the young crawl out into the immediate surroundings.
If most of such pelagic offspring do not survive, either
due to predation or by never finding a suitable habitat,
then it is better to lay eggs that stay in the vicinity,
which is a habitat proven to be suitable for survival.

Of course, the latter method can have the disadvantages of
causing offspring to compete with thier siblings, and also
the possibility of a local disaster whiping out all of
one's offspring. Broadcasting offspring over a wide area
may ensure that some offspring survive somewhere; it also
allows an individual to spread its genes over a wider area.

Peter Egerton, Vancouver, Canada



>Friday   August 20, 1999   11:58 PM
>
>Dear Friend,
>
>Can we consider a mollusk with a veliger phase
>more evolved than a mullusk without it ?
>
>Is the veliger phase a real advantage ?
>
>Are there species with the veliger phase and
>species without it in the same Genus ?
>
>If so, is it correct to consider the species
>without veliger more primitive than the other ones
>( inside the same Genus ) ?
>
>The (Many) Questions Man...
>
>Maurizio.
>
>======================
>       Maurizio A. Perini
>       Via Pedrazza, 9
>       I - 36010 Zane (VI)
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>
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>
>
-------------------------------------------------------
Peter Egerton, Vancouver, Canada
Collector of worldwide Mollusca
http://www.intergate.bc.ca/personal/seashell/index.html
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