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

[Kenneth Kinman]

Hi Les,

       I guess I should reword my description of the radula character.  In any case, if my phylogeny is correct, the first radula would have evolved in the bivalved sacoglossan gastropods.  And their use of that radula is pretty simple---just stab the algal cell and suck out the contents.

                                ------------------Ken


https://en.wikipedia.org/wiki/Juliidae

[https://upload.wikimedia.org/wikipedia/commons/f/fd/Juliidae.png]<https://en.wikipedia.org/wiki/Juliidae>

Juliidae - Wikipedia<https://en.wikipedia.org/wiki/Juliidae>
en.wikipedia.org
Juliidae, common name the bivalved gastropods, is a family of minute sea snails, marine gastropod mollusks or micromollusks in the superfamily Oxynooidea, an ...





________________________________
From: Les Watling <watling at hawaii.edu>
Sent: Friday, November 24, 2017 2:20 PM
To: From: Kenneth Kinman; To: David Campbell; Cc: taxacom at mailman.nhm.ku.edu
Subject: "Subject: Re: [Taxacom] Were bivalves the first molluscs to evolve?"

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
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University of Hawaii at Manoa
Honolulu, HI 96822
Ph. 808-956-8621
Cell: 808-772-9563
e-mail: watling at hawaii.edu<mailto:watling at hawaii.edu>

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