[Taxacom] "Subject: Re: Were bivalves the first molluscs to evolve?"

[Les Watling]

The character order Kinman gives for the radula is backwards for the
gastropods, and most likely also for the chitons. We (Steneck and Watling,
1982, Marine Biology) showed that the snails with the most teeth per row
were feeding on the lightest and easiest food to graze. As the number of
teeth and their robustness changed, so did their food sources, allowing
more deep excavating of harder algae such as the corallines, and the eating
of a wider variety of algal forms.

So, the radula does not become more complex, but it does become more
specialized, allowing for more specificity of food sources, and niche
diversification.

This pattern of reduction of repeated functional units is quite common in
the invertebrate world, and can be seen in worms and arthropods, for
example.

With morphological coding, getting the sequence in the right order is
everything, of course. Functional studies of characters are needed to
establish both the likely order of change but also to get the homologies
correct.


Les Watling
Dept. of Biology
216 Edmondson Hall
University of Hawaii at Manoa
Honolulu, HI 96822
Ph. 808-956-8621
Cell: 808-772-9563
e-mail: watling at hawaii.edu

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