Biology - Chapter 29 “Echinoderms and Invertebrate Chordates”

1. Biology - Chapter 29“Echinoderms and Invertebrate Chordates” Charles Page High School Stephen L. Cotton

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

3. Section 29-1Echinoderms • OBJECTIVES: • Describe the characteristics of the classes of echinoderms.

4. 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.

5. 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”

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

7. 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

8. Section 29-1Echinoderms • Thus, some biologists feel that among invertebrates, echinoderms are most closely related to humans! • Echinoderms are somewhat “ugly”- however, they are very well adapted to life in the sea; have changed very little

9. 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

10. 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

11. 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

12. 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 what it is touching

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

14. 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

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

16. 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

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

18. 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

19. 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

20. 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

21. Section 29-1Echinoderms • However, they can do little more than tell whether it is light or dark • also may have statocysts for balance, telling them whether it is right side up • the spiny surface is not very good protection; good in some such as the crown-of-thorns starfish

22. 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; active at night when most predators sleep

23. 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

24. 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

25. Section 29-1Echinoderms • Reproduction- most echinoderms are either male or female, some are hermaphrodites • place the eggs and sperms in the water where fertilization takes place • the larvae have bilateral symmetry- very advanced

26. Section 29-1Echinoderms • When the larvae mature and metamorphose into adults, they have 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

27. Section 29-1Echinoderms • Echinoderm Classes- 5 classes, although exact names not given • 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

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 longer more flexible arms- thus able to move much more rapid • 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 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 Do 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 embryolgy study, 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.

38. Section 29-2Invertebrate Chordates • OBJECTIVES: • Describe the two subphyla of invertebrate chordates.

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

40. 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

41. 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 life

42. Section 29-2Invertebrate Chordates • 1. 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

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

44. 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 it’s internal organs, muscles, and sense organs

45. Section 29-2Invertebrate Chordates • 3. 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 with the outside

46. 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

47. 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

48. 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

49. 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

50. 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