Basal Mollusca
This section covers almost all of the Mollusca except the three huge clades of
advanced mollusks: Bivalvia, Cephalopoda,
and Gastropoda. The molluscan
way of life is ancient. Some elements of the molluscan body plan go as far
back as the beginnings of the Bilateria.
So, for example, Kimberella, an Ediacaran animal, was quite
mollusc-like. In fact, it may even have had a scraping organ analogous to
a radula. Xenoturbella,
an extremely primitive living animal, is also mollusc-like, although it is
probably a deuterostome. As
with most invertebrate groups, Mollusca lacks a reasonable phylogenetic
definition, so it is somewhat hard to say where the actual "Phylum
Mollusca" begins. As applied in the literature, Mollusca
probably corresponds quite closely to the crown group of all living
"mollusks," i.e. Solenogastres
+ garden snails.
Our coverage of this vast diversity of basal forms is fairly limited.
As the cladogram above indicates, there are a great many holes. We do have
pages on the Solenogastres and the worm-like Caudofoveata,
as well as the chitons and some early
shelled mollusks, the Rostroconchia.
Unfortunately, since most early mollusks lacked shells, the fossil record is
also quite sparse.
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page uploaded 29 September 2002, last modified 28 December
page by
M. Alan Kazlev
checked ATW050731
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