Section 1 Section 1 Echinoderms FocusFocus Overview Objectives Animal Development Before beginning this section ● Compare the developmental If you have been to a saltwater aquarium, you’re sure to have seen review with your students the pattern found in protostomes echinoderms, which are spiny invertebrates that live on the ocean with that found in deuteros- bottom. How could echinoderms like the brittle star shown on the objectives listed in the Student tomes. 8B Edition. This lesson describes the first page of this chapter be related to animals such as chordates, ● Describe the major charac- which are primarily vertebrates? The answer lies in their early devel- similarities and differences between teristics of echinoderms. 8C opment. As an embryo develops, it goes through a gastrula stage. As protostome and deuterostome ● TAKS 2 shown in Figure 1, a gastrula has an opening to the outside called development and introduces stu- Summarize how the sea star’s water vascular system the blastopore. In acoelomate animals, the mouth develops from or dents to the groups of organisms functions. 7B TAKS 3 near the blastopore. This pattern of development also occurs in that show each of these develop- some coelomate animals, such as annelids, mollusks, and arthro- mental patterns. Students will study Key Terms pods. Animals with mouths that develop from or near the blastopore echinoderm structure and function blastopore are called protostomes. and review examples of several dif- protostome Some animals follow a different pattern of development. In phy- ferent groups of echinoderms. deuterostome lums Echinodermata and Chordata, the anus—not the mouth— ossicle develops from or near the blastopore. (The mouth forms later, on water-vascular system another part of the embryo.) Animals with this pattern of develop- Bellringer skin gill ment are called deuterostomes, also shown in Figure 1. If you know Ask students to list the names of as the origin of these two terms, it’s easy to remember the differences many non-fish marine organisms as between the two developmental patterns. The term protostome is they can think of. (Most will be either from the Greek protos, meaning “first,” and stoma, meaning mollusks or echinoderms.) “mouth.” The prefix deutero- is from the Greek deuteros, meaning “second.” In deuterostomes, the anus develops first and the mouth develops second. MotivateMotivate Figure 1 Embryonic development The development of an animal embryo follows one of two patterns. ENERAL Demonstration G Gastrula Gastrula Bring in several preserved or dried specimens of echinoderms such as sea cucumbers, sea stars, and sand Gut EmbryoGut Embryo dollars. You can supplement these Anus Mouth specimens with pictures in books. Allow students to inspect them and come up with as many common Blastopore Blastopore characteristics as they can. List those Coelom Coelom characteristics on the board or overhead, and refer to the list as Blastopore Blastopore you teach the specific characteristics. becomes mouth becomes anus LS Visual TAKS 2 Bio 8C Protostomes Deuterostomes 692 Chapter Resource File Transparencies TT Bellringer • Lesson Plan GENERAL pp. 692–693 • Directed Reading TT Patterns of Embryonic Development TT Evolution of Chordates and Student Edition •Active Reading GENERAL TAKS Obj 2 Bio 8C Echinoderms •Data Sheet for Data Lab GENERAL TAKS Obj 3 Bio 7A TAKS Obj 3 Bio 7B TEKS Bio 7A, 7B, 8B, 8C Planner CD-ROM Teacher Edition TAKS Obj 2 Bio 8C • Reading Organizers TAKS Obj 3 Bio 7A TAKS Obj 3 Bio 7B • Reading Strategies TEKS Bio 5C, 7A, 7B, 8C TEKS Bio/IPC 3C 692 Chapter 31 • Echinoderms and Invertebrate Chordates Sea Sea Brittle Sea Sea TTeacheach Vertebrates Lancelets Tunicates stars lilies stars urchins cucumbers Subphylum Class Class SKILL BUILDER Cephalochordata Crinoidea Echinoidea Subphylum Subphylum Class Class Class Interpreting Visuals Have students Vertebrata Urochordata Asteroidea Ophiuroidea Holothuroidea examine Figure 2. Ask them to iden- tify the first group of echinoderms that evolved (sea cucumbers) and the most recently evolved group(s) of echinoderms. (sea stars, sea lilies, brittle stars) Ask them to identify the evolutionary relationship between echinoderms and chor- Phylum Phylum Figure 2 Evolution of dates—did one evolve from the Chordata Echinodermata chordates and echinoderms. other? (Echinoderms and chordates This phylogenetic tree shows evolved from a common ancestor that the relationship of the major Ancestral was neither an echinoderm nor a deuterostome chordate and echinoderm groups. chordate.) LS Visual TAKS 3 Bio 7A (grade 11 only), 7B; Bio 8B The first deuterostomes were marine echinoderms that evolved more than 650 million years ago. They were also the first animals GENERAL to develop an endoskeleton. Today, most people are familiar with Group Activity echinoderms known as “starfish,” which are not really fish and are Symmetry All adult echinoderms more properly called sea stars. In addition to sea stars, many other display pentaradial symmetry. Penta animals commonly seen along the sea shore—sea urchins, sand dol- means “five.” Therefore, echino- lars, and sea cucumbers—are echinoderms. All are marine, and all derms have five or approximately are radially symmetrical as adults. multiples of five arms. Have groups Chordates, as well as a few other small phyla, are also deutero- of students create displays that stomes. (Humans and all other vertebrates are chordates.) Like the define and model various forms of echinoderms, chordates have an internal skeleton. This develop- symmetry. Encourage them to com- mental similarity unites these seemingly dissimilar animal phyla. It pare objects made by humans with also leads scientists to believe that chordates and echinoderms those found in nature. They can use derived from a common ancestor, as shown in the phylogenetic tree pictures and clay models to make in Figure 2. The identity of the ancestral deuterostome is not known. The fossil record indicates that echinoderms, such as the their comparisons. sea lily in Figure 3, were abundant in the ancient seas. LS Kinesthetic Co-op Learning Bio 5C Evolutionary Milestone Demonstration Display any echinoderms you or 8 Deuterostomes your students may have collected Echinoderms are coelomates that have a deuterostome pattern of such as sea stars or sand dollars. embryo development. The same pattern of development occurs in Emphasize the five-part radial sym- the chordates. Figure 3 Fossil sea lily. Sea lilies such as the one metry of the specimens. Point out preserved by this fossil were that during drying, the skin of sand plentiful in the ancient oceans. dollars disintegrates, and only the 693 hard internal skeleton remains. Ask students how echinoderms differ Trends in Medicine from arthropods. (Echinoderms have Body Part Regeneration The importance endoskeletons, no body segments, and of chemical signals in the development of radial symmetry; arthropods have deuterostomes has significant medical implica- exoskeletons, body segments, and tions for the regeneration of lost body parts. bilateral symmetry.) LS Visual Scientists are working to discover factors that TAKS 2 Bio 8C; Bio 5C cause cells to change and grow so that some- day it might be possible to re-grow a severed spinal cord or an amputated limb. BIOLOGY Bio/IPC 3C; Bio 5C •Unit 7—Exploring Invertebrates This engaging tutorial introduces students to invertebrate structure and function. Chapter 31 • Echinoderms and Invertebrate Chordates 693 Modern Echinoderms Many of the most familiar animals seen along the seashore—sea Real Life stars, sea urchins, sand dollars—are echinoderms. Echinoderms TTeach,each, continuedcontinued Do sand dollars are also common in the deep ocean. While all echinoderms are resemble the sun? marine, the different classes of echinoderms vary considerably in Teaching Tip To the Chumash Indians of the details of their body design. Despite their apparent differences, Sea Urchin Embryology Tell stu- southern California, the all echinoderms share four fundamental characteristics. lines radiating from a sand dents that sea urchins hatch from dollar’s mouth resemble 1. Endoskeleton. Echinoderms have a calcium-rich endoskeleton eggs as microscopic floating larvae. the sun’s rays. Sand dol- composed of individual plates called ossicles . When ossicles These delicate, elegant-looking lars, once plentiful in the first form in young echinoderms, they are enclosed in living tis- creatures have two mirror-image Pacific Ocean, became the sue, so they are a true endoskeleton. Even though the ossicles of Chumash’s symbol adult echinoderms appear to be external, they are covered by a halves, just like beetles, birds and for the “newborn” bats. They float for weeks near the sun of the thin layer of skin (although sometimes the skin is worn away). ocean’s surface fanning even tinier winter solstice. In adult sea stars and in many other echinoderms, a large num- organisms into their mouths. Then, ber of these plates are fused together. The fused plates function much like an arthropod exoskeleton. They provide sites for mus- a change occurs. A small bundle of cle attachment and shell-like protection. In most echinoderms, cells inside the organism begin to the plates of the endoskeleton bear spines that project upward grow. All of the other cells die, and through their skin. the tiny bundle settles to the ocean floor to grow into something that 2. Five-part radial symmetry. All echinoderms are bilaterally sym- metrical as larvae. During their development into adults, the looks like a calcified Koosh Ball larvae’s body plan becomes radially symmetrical. Most adult several inches in diameter. Instead echinoderms, such as the one shown on the left in Figure 4, have of two mirror-image halves (bilat- a five-part body plan with arms that radiate from a central point. eral symmetry) seen in the larva, However, the number of arms can vary. Echinoderms have no the adult urchin is organized more The term echinoderm is head or brain. Instead, the nervous system consists of a central like five equal pie slices (pentara- from the Greek echinos, ring of nerves with branches extending into each of the arms.