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Animals II Part 2 VoiceThread Transcript

Slide 1 The next group of organisms we will look at are members of the protostomes.

Slide 2 Remember that the protostome animals are those animals that show spiral cleavage and determinate cells at the 8-cell stage of development. Later in development, the mouth develops from the blastopore and the anus develops secondarily.

Slide 3 The first group of protostomes we will look at is Phylum Mollusca which includes clams, snails, octopuses and sea slugs. This group is characterized by soft unsegmented bodies and often a shell.

Slide 4 In the mollusks we see a much more complicated body plan than any of the other organisms we have looked at thus far. The basic mollusk body plan consists of a muscular foot, a visceral mass, and a mantle. This drawing depicts the basic anatomy of a mollusk. The foot is used for movement (especially in the gastropods) or as an anchor (as observed in chitons). The visceral mass houses most of the internal organs (e.g., the stomach, gonads, and heart). The mantle is the tissue layer that covers the visceral mass. In organisms that have shells, the mantle produces the shell.

Slide 5 There are four main groups of mollusks. The gastropods include snails, slugs and nudibranchs. This group has both terrestrial and aquatic representatives but the nudibranchs are only aquatic. They often have beautiful colors to advertise that they are highly toxic and should not be eaten.

Slide 6 The bivalves includes mussels, oysters, and clams. They are an aquatic group characterized by two hinged shells. Some of them like the zebra mussel are invasive species that are causing problems in the great lakes. Others like this gooeyduck clam and oyster are prized edibles.

Slide 7 The cephalapods include the octopuses, squid, cuttlefish, and nautiluses. They all have a head surrounded by tentacles that they use for locomotion and grasping prey. The cephalopods have well developed nervous systems - they have excellent vision and are highly intelligent.

Slide 8 Cephalopods have highly advanced behaviors - such as mimicry and mating behavior. This octupus is mimicing a starfish to avoid predation and these squid are involved in an elaborate courtship. No other organisms we have looked at thus far have had these abilities.

Slide 9 Chitons are obscure mollusks that cling to rocks in shallow ocean waters.

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