Chapter 29 Echinoderms and Invertebrate Chordates

1. Chapter 29 Echinoderms and Invertebrate Chordates

2. Section 29-1Echinoderms • OBJECTIVES: • Relate the structure of the echinoderms to essential life functions. • Describe the characteristics of the classes of echinoderms.

3. Section 29-1Echinoderms • Phylum Echinodermata- starfish, sea urchins, sand dollars, etc. • echino- means spiny; dermis means skin • these are spiny-skinned animals • Cambrian period; 580 million yr.

4. Section 29-1Echinoderms • In addition to having spiny skin, they are characterized by: • 5-part radial symmetry • internal skeleton • water vascular system • suction-cuplike structures called tube feet

5. Section 29-1Echinoderms • The internal skeleton (or endoskeleton) is made up of hardened plates of calcium carbonate; often bumpy or spiny. • The water vascular system consists of an internal network of fluid-filled canals connected to the external appendages called tube feet.

6. Section 29-1Echinoderms • The water vascular system is essential for: • feeding; respiration; internal transport; elimination of wastes; and movement. • Echinoderms have an internal skeleton like Chordates, and some similar development.

7. Section 29-1Echinoderms • Thus, some biologists feel that among invertebrates, echinoderms are most closely related to humans! • Echinoderms are very well adapted to life in the sea; some have changed very little in millions of years of evolution.

8. Section 29-1Echinoderms • Adult echinoderms have a body plan with five parts organized symmetrically around a center. • neither anterior nor posterior end; no brain • but, they are two-sided • mouth side is the oral surface

9. Section 29-1Echinoderms • Side opposite the mouth is the aboral surface. • They have a unique system of internal tubes called a water vascular system. • Opens to the outside through a sieve-like structure called the madreporite.

10. Section 29-1Echinoderms • In starfish, the madreporite connects to a tube called the ring canal that forms a circle around the animal’s digestive system. • Figure 29-3, page 639 • From the ring canal, five radial canals extend into each body segment.

11. Section 29-1Echinoderms • Attached to each radial canal are hundreds of movable tube feet. • This entire system acts like a series of living hydraulic pumps that can propel water in or out of the tube feet. • Can create a partial vacuum to hold on to whatever it is touching

12. Section 29-1Echinoderms • Feeding in carnivores, such as starfish, use their tube feet to pry open the shells of bivalve mollusks. • Then the starfish flips the stomach out of its mouth, pours out enzymes, and digests its prey in its own shell; then pulls the stomach back, leaving an empty shell.

13. Section 29-1Echinoderms • Herbivores, such as sea urchins, scrape algae from rocks by using their 5-part jaw. • Filter feeders, such as sea lilies, basket stars, and some brittle stars, use tube feet on flexible arms to capture plankton that float by on ocean currents.

14. Section 29-1Echinoderms • Detritus feeders, such as sea cucumbers, move much like a bulldozer, taking in a mixture of sand and detritus. • Similar to earthworms, they digest the organic material and pass the sand grains out in their feces.

15. Section 29-1Echinoderms • Respiration in most species, the thin-walled tissue of the tube feet forms the main respiratory surface. • In some species, small outgrowths called skin gills also function in gas exchange.

16. Section 29-1Echinoderms • Internal transport (transporting oxygen, food, and wastes which is normally done by a circulatory system) is shared by different systems in echinoderms. • They don’t really need a system for gases, because of gills and skin.

17. Section 29-1Echinoderms • The distribution of nutrients is performed primarily by the digestive glands and the fluid within the body cavity • Excretion in almost all echinoderms, solid wastes are released through the anus (on the aboral surface) as feces.

18. Section 29-1Echinoderms • The nitrogen-containing cellular wastes are excreted primarily as ammonia. • Wastes seem to be excreted in many of the same places around the body in which gas exchange takes place, the tube feet and the skin gills.

19. Section 29-1Echinoderms • Response since they have no head, they have primitive nervous systems. • They do have scattered sensory cells to detect food. • Starfish also have up to 200 light-sensitive cells clustered in eyespots at the tip of each arm.

20. Section 29-1Echinoderms • However, they can do little more than tell whether it is light or dark. • Also may have statocysts for balance, to tell them whether they’re right side up. • The spiny surface is not really very good protection; good only in a few such as the crown-of-thorns starfish.

21. Section 29-1Echinoderms • Many predators have learned that if they turn these animals over, they can attack them through their unprotected underside. • Thus, many echinoderms hide during the day and are active at night when most predators are asleep.

22. Section 29-1Echinoderms • Movement = use tube feet and thin layers of muscle fibers attached to the plates of the endoskeleton to move. • In sand dollars and sea urchins, the plates are fused together to form a rigid box that encloses the animal’s internal organs.

23. Section 29-1Echinoderms • In sea cucumbers, the plates are reduced to tiny vestiges inside a soft, muscular body wall. The loss of the plates makes the body of sea cucumbers very flexible.

24. Section 29-1Echinoderms • Reproduction = most echinoderms are either male or female, although some are hermaphrodites. • Egg and sperm are released and fertilization takes place in the water. • The larvae have bilateral symmetry= very advanced.

25. Section 29-1Echinoderms • When the larvae mature and metamorphose into adults, they develop radial symmetry. • Many starfish have incredible powers of regeneration. • Each piece can grow into a new animal as long as it contains a portion of the central part.

26. Section 29-1Echinoderms • Almost 6,000 species found in almost every ocean (salt water) in the world. • No echinoderms have ever entered fresh water, and they cannot survive for long on land.

27. Section 29-1Echinoderms • Echinoderm Classes • Starfish • Brittle Stars • Sea Urchins and Sand Dollars • Sea Cucumbers • Sea Lilies and Feather Stars

28. Section 29-1Echinoderms • 1. Starfish = this class contains the common starfish, which are also known as sea stars. • Some have more than 5 arms • Figure 29-7, page 642 • Carnivorous, preying upon the bivalves they encounter

29. Section 29-1Echinoderms • 2. Brittle Stars = live in tropical seas, especially on coral reefs • Look like common starfish, but have longer, more flexible arms, thus able to move much more rapidly • Protection by shedding one or more arms when attacked; are filter and detritus feeders

30. Section 29-1Echinoderms • 3. Sea Urchins and Sand Dollars = includes disk-shaped sand dollars, oval heart urchins, and round sea urchins. Fig. 29-8, p. 643 • Are grazers that eat large quantities of algae; may burrow into the sand or mud; may protect themselves by long sharp spines.

31. Section 29-1Echinoderms • 4. Sea Cucumbers = look like warty moving pickles, with a mouth at one end and an anus at the other. • Figure 29-9, page 644 top • Most are detritus feeders • Some produce a sticky material to “glue” a predator helpless

32. Section 29-1Echinoderms • 5. Sea Lilies and Feather Stars = filter feeders, have 50 or more long feathery arms. • The most ancient class of echinoderms; not common today, but once were widely distributed. • Sea lilies; sessile animals, p.644

33. Section 29-1Echinoderms • How Echinoderms Fit Into the World: • Starfish are important carnivores, controlling other animal populations; a rise or fall in numbers affects other populations.

34. Section 29-1Echinoderms • For example, several years ago the coral-eating crown-of-thorns starfish suddenly appeared in great numbers in the Pacific Ocean. • Within a short period of time, they caused extensive damage to many coral reefs.

35. Section 29-1Echinoderms • In many coastal areas, sea urchins are important because they control distribution of algae. • In various parts of the world, sea urchin eggs and sea cucumbers are considered delicacies by some people.

36. Section 29-1Echinoderms • Several chemicals from starfish and sea cucumbers are currently being studied as potential anti-cancer and anti-viral drugs. • Sea urchins have been helpful in embryology studies, since they produce large eggs; fertilize externally; develop in sea water.

37. Section 29-2Invertebrate Chordates • OBJECTIVES: • Name and discuss the three distinguishing characteristics of chordates. • Describe the two subphyla of invertebrate chordates.

38. Section 29-2Invertebrate Chordates • The phylum Chordata, to which fishes, frogs, birds, snakes, dogs, cows, and humans belong, will be discussed in future chapters. • Most chordates are vertebrates, which means they have backbones, and are placed in the subphylum Vertebrata.

39. Section 29-2Invertebrate Chordates • But, there are also invertebrate chordates; these are divided into two subphyla: • 1. The tunicates • 2. The lancelets • Due to similar structures, the chordate vertebrates and invertebrates may have evolved from a common ancestor.

40. Section 29-2Invertebrate Chordates • Chordates are animals that are characterized by a notochord, a hollow dorsal nerve cord, and pharyngeal (throat) slits. • Some chordates posses these characteristics as adults; others as only embryos; but all have them at some stage of development.

41. Section 29-2Invertebrate Chordates • Notochord = a long, flexible supporting rod that runs through at least part of the body, usually along the dorsal surface just beneath the nerve cord. • Most chordates only have this during the early part of embryonic life.

42. Section 29-2Invertebrate Chordates • Vertebrates will replace the notochord quickly with the backbone. • The second chordate characteristic, the hollow dorsal nerve cord, runs along the dorsal surface just above the notochord.

43. Section 29-2Invertebrate Chordates • In most chordates, the front end of this nerve cord develops into a large brain. • Nerves leave this cord at regular intervals along the length of the animal, and connect its internal organs, muscles, and sense organs.

44. Section 29-2Invertebrate Chordates • The third chordate characteristic, the pharyngeal slits, are paired structures in the pharyngeal (or throat) region of the body. • In aquatic chordates, such as lancelets and fishes, the pharyngeal slits are gill slits that connect the pharyngeal cavity with the outside.

45. Section 29-2Invertebrate Chordates • In terrestrial chordates that use lungs for respiration, pharyngeal slits are present for only a brief time during the development of the embryo. • They soon close up as the embryo develops. Page 283.

46. Section 29-2Invertebrate Chordates • In humans, pouches form in the pharyngeal region, but never open up to form slits. • Thus, some scientists consider the pharyngeal pouches, not slits, as the “true” chordate characteristic.

47. Section 29-2Invertebrate Chordates • Tunicates = small marine chordates that eat plankton they filter from the water. • Name from a special body covering called the tunic. • Only the tadpole-shaped larvae have the notochord and dorsal nerve cord.

48. Section 29-2Invertebrate Chordates • Examples of tunicates are the sea squirts. Figure 29-11, page 646. • Adults are sessile, living as colonies attached to a solid surface; larvae are free swimming.

49. Section 29-2Invertebrate Chordates • Lancelets = small fishlike creatures; live in sandy bottoms of shallow tropical oceans. • Unlike tunicates, the adult lancelets have a definite head; a mouth that opens into a long pharyngeal region with up to 100 pairs of gills.

50. Section 29-2Invertebrate Chordates • Figure 29-12, page 646 • They feed by passing water through their pharynx, where food particles are caught in a sticky mucus; lack any jaws. • They have a primitive heart pumping blood through closed circulation.