well,
the debates is actually interesting! Maybe a little too technical to some.
Anyway, may I add my two cents. What am I used to do when I meet two shells
with different protoconch and nearly identical teleoconch? ...the answer at
the end of this message.

The science of interpreting and understanding the evolution of larval
development still lacks a crucial info: the genetics controlling these
features of the development. We don't know wheter there is a single gene
for the planktotrophy, or a cluster of coordinated genes, or even
independet genes operating to produce the extended velum, the cilia, the
feeding mouth etc...
And what about the egg production? What gene(s) is(are) operating to
produce a planktotrophic embryo? And is just a matter of maternal effect? I
mean, the gene(s) of the mother determine the kind of egg (planktotrophic
vs. lecithotrophic), then the fate of the daugther larva is already
determined in the genes of the mother... ?? In turn what about her sons.
And finally (??) what about the influence of the environment? Can the
environmental parameters influence the direction of development?
The accumulated experience on the pairs suggest that two populations with
different development very likely represent two distinct species under the
biological species concept. But the sole indication that they develop in a
different way is NOT a definitive proof. It simply indicate that they have
some different biological properties, NOT hat they are two distinct and
isolated gene pools. Most cases (but they're very very few!!) so far
examined by independent tools (allozyme, DNA)  seem to indicate different
species. I have diagnosed by allozymes Columbella rustica (Mediterranean,
lecithotrophic L) from Columbella adansoni (Atlantic, planktotrophic P)
otherwise indistinguishable (except protoconch of course).
OLIVERIO M., 1995. Larval development and allozyme variation in the East
Atlantic Columbella (Gastropoda: Prosobranchia: Columbellidae). Scientia
Marina, 52(1):77-86.
But I have failed attempting to separate by the same markers Rissoa
auriscalpium (P) from Rissoa italiensis (L) and R. rhodensis (L), and
Rissoa violacea (P) from Rissoa sp. (L), either in allopatry or in sympatry.
OLIVERIO M., 1994. Developmental vs. genetic variation in two rissoid
gastropod complexes. Journal of Molluscan Studies, 60: 461-465.
At this regard a colleague tells me he has some indication from finer DNA
markers (SNIPS) that the two sympatric populations of Rissoa from the Gulf
of Naples (auriscalpiumP/italiensisL) are diagnosed (hope he publishes
soon!!).

I have summarized my ideas in:
OLIVERIO M., 1996. Contrasting developmental strategies and speciation in
N.E. prosobranchs: a preliminary analysis. In (J.D. Taylor ed.) Origin and
evolutionary radiation of the Mollusca. Chpt. 22, pp. 261-266. Oxford
University Press.
OLIVERIO M., 1996. Life-histories, speciation and biodiversity in
Mediterranean prosobranchs gastropods. Vie et Mileu, 46(2): 163-169.

And the global scale of the phenomenon and its relevance in recently
modelling the patterns of biodiversity in:

OLIVERIO M., 1997. Global biodiversity and life-history evolution in
prosobranchs gastropods. Iberus, 16: 73-79.

My personal position and practice as concerns taxonomy is the following: I
use different names for populations of caenogastropods with different
development (thus protoconch). It is - in my opinion - the most
conservative position, I would say the most parsimonious. Admitting
poecilogony, giving the present knoledge (still scarce) would require to
hold assumptions that are evolutionary more ... expensive. This is just my
personal position, that I know is shared my many, but I can't tell if we
are the majority ... nor if we are rigth.

But the discussion is STILL OPEN: Nature does not like to conform to our
rigid schemes of B/W, +/_, either/or, plankt/lecith. Often - more often
than we realize - the grey area is full of interesting critters ....



=========================================================
Marco Oliverio - Evolutionary Biology PhD
Research Scientist

Dipartimento di Biologia Animale e dell'Uomo
Viale dell'Universita' 32
I-00185 Roma   ITALY

phone  +39.06.49914307
FAX    +39.06.4958259
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