BIOL 321 Lecture Notes - Lecture 16: Anatomical Terms Of Location, Monoplacophora, Mollusca
7 Nov 2016
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Document Summary
Monoplacophorans are quite rare and mostly live in the ocean. Note: multiple pairs of muscle scars on the inside of the fossil shell. Have 5-8 pairs of metanephridia; also have multiple pairs of ctenidia/gills. Also have many pairs of dorso-ventral shell retractor muscles. Shell as protective retreat: tall cone; asymmetrical coiling. Gradually over time is elongates along its dorso-ventral axis forming a tall cone, and simultaneously the aperture of the shell narrows and then thirdly it starts to undergo coiling. The shell and all of the viscera contained coil asymmetrically. So a spire consisting of all the earlier shell coils spits out the one side: operculum & columellar muscle. As the shell coils are laid down, there is a central pillar of calcium carbonate that"s formed along the central coiling axis. Have shell attached dorso-ventral shell retractor muscles but have only a single pair of shell-attached muscles, in fact most have just a single one.
