BIOL 1101 Lecture Notes - Lecture 3: Body Plan, Mollusca, Chiton
10 May 2016
School
Department
Course
Professor
Document Summary
Like the annelida, the mollusca are: eucoelomate, protostomes. 3. lophophorates: bilaterally symmetrical, cephalized, have a complete gut. But unlike the annelids, they are not segmented. There are 80,000 or more living species of mollusks, and because of their shells, they also probably have the best fossil record of any group (about 35,000 species). Mollusks range in size from microscopic bivalves to giant squids 60 feet or more in length. They inhabit all marine and many freshwater and terrestrial environments. The four classes of mollusca covered in class: polyplacophora chitons, gastropoda snails and slugs, bivalvia clams, mussels, etc, cephalopoda squids, octopuses. The wormlike annelid structure was easy to understand; mollusks are a little more complex, and some have been highly modified by evolution. The basic molluscan body plan (and perhaps ancestral body plan) is like a sandwich. The bulk of the animal, including the head and all the internal organs, is the visceral mass, and is the middle of the sandwich.
