I keep this topic within the list since I guess there may be someone else
interested.

The evolution of larval planktotrophy in the Mollusca is a very interesting
issue, as it is in the Animals in general.
Within the Mollusca larval planktotrophy has evolved in the Bivalvia AFTER
the protobranchs, that is the bivalves originated as lecithotrophs and only
secondarily planktotrophy appeared.
The sole other class where larval planktotrophy is known is Gastropoda. All
other classes seem to have only lecithotrophic development, indicating that
this is the primitive state in the Mollusca.
Also within the gastropods, "primitive" gastropods were lecithotrophs,
planktotrophy evolving only secondarily and independently in neritimorphs,
caeanogastropods and heterobranchs.
Within the *Archaeogastropoda* to my knowledge there is no instance of
larval planktotrophy, other than the neritimorphs. Nature is funny, and
often likes to play with us, but in this case I would bet there is no
exception. Abalone are one of the cases where true larval feeding (larval
planktotrophy) is not possible, but larval uptake of DOM (dissolved organic
matter, that includes even aminoacids!) from sea-water is documented. That
is, the larvae are not able to feed actively, but get some organic
compounds from the seawater thru the "skin". This means that - contrarily
to what has often been assumed - biology of these lecithotrophic larvae is
not completely decoupled from environmental parameters.
an old - yet very nice - reference to this argument is:
JAECKLE W.B. and D.T. MANAHAN, 1989. Feeding by a "nonfeeding" larva:
Uptake of dissolved amino acids from seawater by lecithotrophic larvae of
the gastropod Haliotis rufescens.Marine Biology, 103: 87-94.

all the best






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

Dipartimento di Biologia Animale e dell'Uomo
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