3454lablecture4 - Lecture 4 PHYLUM MOLLUSCA Triploblastic...

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Lecture 4 PHYLUM MOLLUSCA Triploblastic, bilateral symmetry, coelomate, one of the largest phyla Coelom formed thru schizocoely 2 main body regions: Head/foot and visceral mass Protostomes – blastopore forms mouth first in development Most have protective shell (called a valve) Can be lost or modified Most have radula for feeding Gills (ctenidia) can be lost or modified CLASS GASTROPODA (Snails and slugs) One pair of ctenidia Univalve Radula scrapes algae – some can drill or stab (Poisonous Cone Shells) Glide on mucus trail using muscular foot Torsion – visceral mass rotates 180° so anus and gills are positioned above the head Happens in development, may keep ctenidia free of debris, allows whole body to be retracted into shell SUBCLASS PROSOBRANCHIA Sea Snails, ctenidia intact, foot operculum for defense SUBCLASS OPISTHOBRANCHIA Sea Slugs, Sea Hares No shell
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Torsion is reversed Lost ctenidia and evolved secondary gills called pseudobranchs Can eat cnidaria to incorporate nematocysts for defense
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3454lablecture4 - Lecture 4 PHYLUM MOLLUSCA Triploblastic...

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