Marien,
If the change from one mode of larval development to another is widespread in
 marine molluscs, and it causes a change from one species to a pair of sister
 species, then this may be a fairly random change that occasionally succeeds.
 Given enough time and species, it is common where there is an advantage in
 keeping larvae local.  Where there is no advantage, the change probably does
 not succeed, as it competes too much with the parent form.  Those random cases,
 which may be seen as unsuccesful "hopeful monsters", could perhaps be
 best described as poecilogony.  If they were successful, they would eventually
 be different species.  Species, however, must have a viable population to
 continue reproducing.  One individual does not a species make, although it may
 be the start.



Allen Aigen
[log in to unmask]