Ch33 Deuterostomes - 33 Deuterostome Animals 33.1 What Is a...

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33 Deuterostome Animals
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33.1 What Is a Deuterostome? Deuterostomes are triploblastic, coelomate animals with internal skeletons.
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33.1 What Is a Deuterostome? Living deuterostomes comprise three clades: Echinoderms —sea stars, sea urchins, and their relatives Hemichordates —acorn worms and pterobranchs Chordates —sea squirts, lancelets, and vertebrates
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Figure 33.1 Phylogeny of the Deuterostomes
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33.1 What Is a Deuterostome? The earliest deuterostomes were bilaterally symmetrical, segmented, and had a pharynx with slits through which water flowed. Echinoderms evolved their unique symmetry later; other deuterostomes retained bilateral symmetry.
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33.2 What Are the Major Groups of Echinoderms and Hemichordates? Only six of 23 groups of echinoderms known from fossils survive today. Nearly all are marine. Hemichordates: 100 living species. These two groups are the ambulacrarians . The ciliated larvae have bilateral symmetry. Adult hemichordates also are bilaterally symmetrical.
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33.2 What Are the Major Groups of Echinoderms and Hemichordates? Echinoderm adults develop pentaradial symmetry (in fives or multiples of fives). Echinoderms have no head, and move equally well in many directions. They have an oral side containing the mouth, and an aboral side containing the anus.
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Figure 33.3 Echinoderms Are Bilaterally Symmetrical as Larvae but Radially Symmetrical as Adults (Part 2)
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33.2 What Are the Major Groups of Echinoderms and Hemichordates? Echinoderms have a system of internal calcified plates covered by thin layers of skin and some muscle. The plates fuse to form an internal skeleton .
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33.2 What Are the Major Groups of Echinoderms and Hemichordates? The water vascular system is a network of water-filled canals leading to extensions called tube feet . Functions: Gas exchange, locomotion, and feeding. Water enters through the madreporite , which is connected to the ring canal around the esophagus. Radial canals radiate out from the ring canal.
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Figure 33.3 Echinoderms Are Bilaterally Symmetrical as Larvae but Radially Symmetrical as Adults (Part 3)
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33.2 What Are the Major Groups of Echinoderms and Hemichordates? Crinoids (sea lilies and feather stars) were more abundant 300–500 Mya. Sea lilies (80 species) attach to the substratum by a stalk Feather stars (600 species) grasp the substratum with flexible appendages that allow limited movement
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33.2 What Are the Major Groups of Echinoderms and Hemichordates? Echinozoans (sea urchins and sea cucumbers): Sea urchins lack arms and are covered with spines that attach to the underlying skeleton by ball-and-socket joints. The spines are moveable, and used for locomotion; some produce toxins. Sand dollars are flattened relatives of sea urchins.
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and Hemichordates? Sea cucumbers lack arms, body is
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This note was uploaded on 03/30/2011 for the course MATHMATICS 1101 taught by Professor Zhong during the Spring '11 term at Georgia State.

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Ch33 Deuterostomes - 33 Deuterostome Animals 33.1 What Is a...

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