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Echinoderms and Invertebrate Chordates Chapter 31 Table of Contents Section 1 Echinoderms Section 2 Invertebrate Chordates

Section 1 Echinoderms Chapter 31 Objectives • Comparethe developmental pattern found in protostomes with that found in deuterostomes. • Describethe major characteristics of echinoderms. • Summarizehow the sea star’s water vascular system functions.

Section 1 Echinoderms Chapter 31 Animal Development • As an embryo develops, it goes through a gastrula stage. A gastrula has an opening to the outside called the blastopore. • Animals with mouths that develop from or near the blastopore are called protostomes. • In phylums Echinodermata and Chordata, the anus—not the mouth—develops from or near the blastopore. (The mouth forms later, on another part of the embryo.) Animals with this pattern of development are called deuterostomes.

Section 1 Echinoderms Chapter 31 Patterns of Embryonic Development

Section 1 Echinoderms Chapter 31 Animal Development, continued • The first deuterostomes were marine echinoderms that evolved more than 650 million years ago. They were also the first animals to develop an endoskeleton. • Like the echinoderms, chordates have an internal skeleton. This developmental similarity unites these seemingly dissimilar animal phyla. • The identity of the ancestral deuterostome is not known.

Section 1 Echinoderms Chapter 31 Animal Development, continued This phylogenetic tree shows the relationship of the major chordate and echinoderm groups.

Section 1 Echinoderms Chapter 31 Characteristics of Echinoderms Click below to watch the Visual Concept. Visual Concept

Section 1 Echinoderms Chapter 31 Modern Echinoderms • Many of the most familiar animals seen along the seashore—sea stars, sea urchins, sand dollars—are echinoderms. • Echinoderms have a calcium-rich endoskeleton composed of individual plates called ossicles. • All echinoderms are bilaterally symmetrical as larvae. During their development into adults, the larvae’s body plan becomes radially symmetrical.

Section 1 Echinoderms Chapter 31 Pentaradial Symmetry

Section 1 Echinoderms Chapter 31 Modern Echinoderms, continued • Echinoderms have a waterfilled system of interconnected canals and thousands of tiny hollow tube feet called a water-vascular system. • The echinoderm body cavity functions as a simple circulatory and respiratory system. • Skin gills are small, fingerlike projections that grow among the echinoderm’s spines. These projections create an increased surface area through which respiratory gases can be exchanged.

Section 1 Echinoderms Chapter 31 Water Vascular System Click below to watch the Visual Concept. Visual Concept

Section 1 Echinoderms Chapter 31 Anatomy of a Sea Star

Section 1 Echinoderms Chapter 31 Anatomy of a Sea Star Click below to watch the Visual Concept. Visual Concept

Chapter 31 Section 1 Echinoderms Types of Echinoderms Click below to watch the Visual Concept. Visual Concept

Section 1 Echinoderms Chapter 31 Echinoderm Diversity Sea Stars • Almost all species of sea stars are carnivores, and they are among the most important predators in many marine ecosystems. • The ossicles of many species of sea stars produce pincerlike structures called pedicellaria. • Pedicellaria contain their own muscles and nerves, and they snap at anything that touches them. This action prevents small organisms from attaching themselves to the surface of the sea star.

Section 1 Echinoderms Chapter 31 Echinoderm Diversity, continued Brittle Stars • The sea star’s relatives, the brittle stars and sea baskets, make up the largest class of echinoderms. • Brittle stars have slender branched arms that they move in pairs to row along the ocean floor. • Although a few species are predators, most brittle stars are filter feeders or feed on food in the ocean sediment.

Section 1 Echinoderms Chapter 31 Echinoderm Diversity, continued Sea Lilies and Feather Stars • The sea lilies and feather stars are the most ancient and primitive living echinoderms. • They differ from all other living echinoderms because their mouth is located on their upper, rather than lower, surface. • Sea lilies are sessile and are attached to the ocean floor by a stalk. Feather stars use hooklike projections to attach themselves directly to the ocean bottom or a coral reef.

Section 1 Echinoderms Chapter 31 Echinoderm Diversity, continued Sea Urchins and Sand Dollars • The sea urchins and sand dollars lack distinct arms but have the basic five-part body plan seen in other echinoderms. • Both sea urchins and sand dollars have a hard, somewhat flattened endoskeleton of fused plates covered with spines protruding from it. • Sea urchins are found on the ocean bottoms while sand dollars live in sandy areas along the sea coast.

Section 1 Echinoderms Chapter 31 Echinoderm Diversity, continued Sea Cucumbers • Sea cucumbers are soft-bodied, sluglike animals without arms. They differ from other echinoderms in that their ossicles are small and are not fused together. • The sexes of most sea cucumbers are separate, but some species are hermaphrodites. • Sea cucumbers feed by trapping tiny organisms present in the sea water. Their mouth is surrounded by several dozen tube feet modified into tentacles.

Section 1 Echinoderms Chapter 31 Echinoderm Diversity, continued Sea Daisies • In 1986, a new class of echinoderm was discovered: strange diskshaped little animals called sea daisies. • Sea daisies have five-part radial symmetry but no arms. • Their tube feet are located around the edges of the disk rather than along the radial lines, like they are in other echinoderms.

Section 2 Invertebrate Chordates Chapter 31 Objectives • Describethe characteristics of chordates. • Definethe term invertebrate chordate. • Comparetunicates and lancelets.

Section 2 Invertebrate Chordates Chapter 31 The Chordate Skeleton • The second major group of deuterostomes are the chordates. Chordates have a very different kind of endoskeleton from that of echinoderms. • During the development of the chordate embryo, a stiff rod called the notochord develops along the back of the embryo. • Using muscles attached to this rod, early chordates could swing their backs from side to side, enabling them to swim through the water.

Section 2 Invertebrate Chordates Chapter 31 The Chordate Skeleton, continued Other Chordate Characteristics • Chordates have a single, hollow, dorsal nerve cord with nerves attached to it that travel to different parts of the body. • Chordates also have a series of pharyngeal pouches that develop in the wall of the pharynx, the muscular tube that connects the mouth to the digestive tract and windpipe. • Another chordate characteristic is a postanal tail, which is a tail that extends beyond the anus.

Section 2 Invertebrate Chordates Chapter 31 Parts of a Chordate Click below to watch the Visual Concept. Visual Concept

Section 2 Invertebrate Chordates Chapter 31 Lancelet Interior

Section 2 Invertebrate Chordates Chapter 31 Anatomy of a Lancelet Click below to watch the Visual Concept. Visual Concept

Section 2 Invertebrate Chordates Chapter 31 Invertebrate Chordates • The vast majority of chordate species belong to subphylum Vertebrata. • Two other subphyla, Urochordata (the tunicates) and Cephalochordata (the lancelets), contain a small number of species. • Because members of these two subphyla are chordates that do not have backbones, they are called invertebrate chordates.

Section 2 Invertebrate Chordates Chapter 31 Characteristics of Invertebrate Chordates Click below to watch the Visual Concept. Visual Concept

Section 2 Invertebrate Chordates Chapter 31 Invertebrate Chordates, continued Tunicates • Most adult tunicates are sessile, filter-feeding marine animals. A tough sac, called a tunic, develops around the adult’s body and gives tunicates their name. • Cilia beating within the tunicate cause water to enter the incurrent siphon. As water passes through the slits in the pharynx, food is filtered from it and passed into the stomach. • All tunicates are hermaphrodites, and some are also able to reproduce asexually by budding.

Section 2 Invertebrate Chordates Chapter 31 Adult Tunicate

Section 2 Invertebrate Chordates Chapter 31 Anatomy of a Tunicate Click below to watch the Visual Concept. Visual Concept

Section 2 Invertebrate Chordates Chapter 31 Invertebrate Chordates, continued Lancelets • Lancelets receive their name from their bladelike shape. Although lancelets may resemble fish, they are not fish. • The lancelets V-shaped bundles of muscles are arranged in a series of repeating segments. • Lancelets feed on microscopic protists that they filter out of the water. Unlike tunicates, the sexes are separate in lancelets.

Standardized Test Prep Chapter 31 Multiple Choice The diagram below shows a vertical cross section of an adult tunicate. Use the diagram to answer questions 1–3.

Standardized Test Prep Chapter 31 Multiple Choice, continued 1. This organism is in the same phylum as A. sea anemones. B. sea cucumbers. C. sponges. D. humans.

Standardized Test Prep Chapter 31 Multiple Choice, continued 2. Which chordate characteristic does this organism have as an adult? F. pharyngeal slits G. dorsal nerve cord H. notochord J. postanal tail

Standardized Test Prep Chapter 31 Multiple Choice, continued 3. What is the significance of the relationship between structures A and B? A. B releases undigested food into the water that leaves the body through A. B. B releases gametes into the water that leaves the body through A. C. B collects food from the water that enters the body through A. D. B extracts oxygen from the water that enters the body through A.

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