Biology - Chapter 27 “Mollusks and Annelids”

1. Biology - Chapter 27“Mollusks and Annelids” Charles Page High School Stephen L. Cotton

2. Section 27-1Mollusks • OBJECTIVES: • Explain how mollusks perform their essential life functions.

3. Section 27-1Mollusks • OBJECTIVES: • Describe and give examples of the three major classes of mollusks.

4. Section 27-1Mollusks • OBJECTIVES: • Discuss how mollusks affect humans and other living things.

5. Section 27-1Mollusks • Phylum Mollusca- soft-bodied with an internal or external shell • evolved in the sea over 600 million years ago • have had a long and successful adaptive radiation • more than 100,000 species today

6. Section 27-1Mollusks • live everywhere, from deep ocean trenches to tree tops • range in size from snails as small as grains of sand to giant squids more than 20 meters • differently looking; but grouped together because of similar development patterns

7. Section 27-1Mollusks • Most have a special kind of larvae called a trochophore- swim in open water, and feed on tiny floating plants • Figure 27-2, page 586 • trochophore larvae also present in the annelids, which are also in this chapter

8. Section 27-1Mollusks • Mollusks are soft-bodies animals with either an internal or external shell • name comes from the Latin word molluscus, meaning soft • some today lack shells (like slugs), but thought to have evolved from shelled ancestors

9. Section 27-1Mollusks • Body plan consists of four basic parts: (Figure 27-3, page 586) • 1. Foot • 2. Mantle • 3. Shell • 4. Visceral mass

10. Section 27-1Mollusks • 1. Foot- the soft muscular foot usually contains the mouth and other structures associated with feeding • can take many different shapes- flat for crawling; spade-shaped for burrowing; tentacles for capturing prey

11. Section 27-1Mollusks • 2. Mantle- a thin, delicate tissue layer that covers most of a mollusk’s body- much like a cloak • 3. Shell- found in almost all mollusks; made by glands in the mantle that secrete calcium carbonate (CaCO3)

12. Section 27-1Mollusks • 4. Visceral mass- located just below the mantle in most mollusks- this area contains the internal organs • These basic body parts have taken on different forms as mollusks adapted to different habitats

13. Section 27-1Mollusks • The type of foot, and the kind of shell that mollusks have are used to group them into the classes we will study • Feeding: many types of feeding have developed, and they feed on many different kinds of food

14. Section 27-1Mollusks • Most mollusks are herbivores, carnivores, or filter feeders- but a few are detritus feeders and others are parasites • some, such as the snails and slugs, feed with a tongue-shaped structure called a radula, which is rough like sandpaper • Figure 27-4, page 587

15. Section 27-1Mollusks • Mollusk herbivores use the radula to scrape algae off rocks in the water, or to eat the buds, roots, and flowers of plants • Mollusk carnivores use the radula to drill through the shells of other animals, then swallow the soft tissues inside

16. Section 27-1Mollusks • In a carnivorous snail called “cone shells”, the tiny rasping teeth of the radula have evolved into long, hollow darts that are attached to a poison gland- can stab prey such as small fish • octopus and sea slugs typically use sharp jaws to eat their prey

17. Section 27-1Mollusks • Mollusks such as clams, oysters, and scallops are filter feeders, using their feathery gills to sift food from the water • cilia on the gills move the mixture of mucus and food into the mouth

18. Section 27-1Mollusks • Respiration: gills serve as the organs of respiration, as well as filters for food • most only use gills for breathing • aquatic mollusks include snails, clams, octopus- use gills inside the mantle cavity

19. Section 27-1Mollusks • Land mollusks such as land snails and slugs breathe by using a specially adapted mantle cavity that is lined with many blood vessels • this surface is kept moist so that oxygen can enter the cells • snails and slugs live in moist areas for this reason

20. Section 27-1Mollusks • Internal Transport: oxygen and nutrients are transported by the blood to all parts of the body • pumped by a simple heart through an “open circulatory system” • the blood is not always in blood vessels, but in sinuses

21. Section 27-1Mollusks • Open circulatory systems work well for slow-moving or sessile mollusks like snails or clams • but faster-moving mollusks such as the octopi and squids have a closed circulatory system, in which blood always moves inside blood vessels

22. Section 27-1Mollusks • Excretion: like other animals, mollusks must eliminate wastes • undigested food becomes solid waste that leaves through the anus in the form of feces • cellular metabolism produces nitrogen-containing waste as ammonia

23. Section 27-1Mollusks • Ammonia is quite poisonous, thus must be removed from body fluids • this is done by tube-shaped organs called nephridia • the nephridia remove ammonia from the blood, and release it to the outside

24. Section 27-1Mollusks • Response: mollusks vary greatly in complexities of their nervous systems, and ability to respond to environmental conditions • clams and other two-shelled mollusks are basically inactive, burrowing in mud or sand • have simple nervous systems

25. Section 27-1Mollusks • These inactive forms may have several small ganglia near the mouth • a few nerve cords • simple sense organs such as chemical and touch receptors; statocysts (for balance); and ocelli (eyespots)

26. Section 27-1Mollusks • Octopi and other tentacled mollusks are active and intelligent predators • have the most highly developed nervous systems of all members of their phylum • may be more intelligent than even some vertebrates!

27. Section 27-1Mollusks • They have numerous sense organs that help them distinguish shapes by sight, and texture by touch • Octopi can be trained to perform different tasks in order to obtain a reward, or avoid punishment

28. Section 27-1Mollusks • Reproduction: in most mollusks, the sexes are separate, and fertilization is external • in snails and almost all two-shelled mollusks, they release eggs and sperm into open water in enormous numbers

29. Section 27-1Mollusks • In tentacled mollusks and certain snails, fertilization takes place inside the body of the female • some other hermaphroditic mollusks, such as certain oysters, switch from one sex to the other- sometimes producing eggs, and sometimes sperm

30. Section 27-1Mollusks • 1. Class Gastropoda- are called gastropods, the name meaning stomach foot • appropriate name because they move by means of a broad, muscular foot located on the ventral (stomach) side

31. Section 27-1Mollusks • Gastropods include familiar pond snails and land slugs, as well as more exotic mollusks such as abalones, sea butterflies, sea hares, and nudibranchs • Figure 27-8, page 590

32. Section 27-1Mollusks • Many gastropods have a one-piece shell that protects their soft bodies • when threatened, many snails can pull up completely into their coiled shells • some have small shells, or like slugs- lack shells completely

33. Section 27-1Mollusks • Most of these without shells are not completely helpless • they are protected by behavior, spending daylight hours under rocks or logs • some sea hares have a special “ink” they squirt into the surrounding water

34. Section 27-1Mollusks • Others, such as the sea butterflies, escape predators by swimming rapidly • many nudibranchs (or sea slugs), have chemicals in their bodies that taste bad or are poisonous; some even have nematocysts to sting with

35. Section 27-1Mollusks • The bad-tasting, poisonous, stinging, or otherwise booby-trapped nudibranchs are usually bright colored- this warns the predators to stay away • thus, the shell-less gastropods do have means of protection

36. Section 27-1Mollusks • 2. Class Bivalvia- have two shells that are hinged together at the back and held together by one or two powerful muscles • common bivalves include clams, oysters, and scallops • may be tiny, or like the giant clam 1.9 meters in length

37. Section 27-1Mollusks • Although bivalve larvae are free-swimming, they soon establish life at the bottom of a body of water • some secrete sticky threads to attach themselves to rocks • most sessile; however scallops can flap their shells to move

38. Section 27-1Mollusks • Mantles of bivalves, like other mollusks, contain glands that manufacture the shells, and also keep the shell’s inside surface smooth and comfortable by secreting layers of mother-of-pearl

39. Section 27-1Mollusks • If a foreign object (sand or a pebble) gets caught between mantle and shell- the mantle covers it with this secretion • after time, these objects become completely coated, and are called pearl • often very valuable

40. Section 27-1Mollusks • 3. Class Cephalopoda- called cephalopods, are among the most active and interesting • includes octopi, squids, cuttlefish, and nautiluses • cephalopoda means head-foot; their head is attached to the foot, divided into tentacles

41. Section 27-1Mollusks • Cephalopods range in size from tiny cuttlefish less than 2 cm long, to giant squids which are thought to grow greater than 20 meters long • they have flexible tentacles equipped with round sucking disks to grab fish and prey

42. Section 27-1Mollusks • Most modern cephalopods have small internal shells, or no shells at all • the only present-day cephalopod with a shell are a few species of nautiluses • Figure 27-11, page 592

43. Section 27-1Mollusks • Cuttlefish have small shells that are found inside their bodies- thin and coiled • this is the cuttlebone on which pet birds condition their beaks • this helps the nautilus and cuttlefish to remain upright and allow it to float in the water - Figure 27-12, page 593

44. Section 27-1Mollusks • However, there are other means of protection for cephalopods • can move quickly, either by swimming or crawling, or a form of “jet propulsion” of drawing water in and then out • changing their color; releasing dark, foul-tasting ink

45. Section 27-1Mollusks • How Mollusks fit into the World: • feed on plants; prey on animals; “clean up” their surroundings by eating detritus • some are hosts to symbiotic algae or to parasites; others are parasites themselves • food for many, even humans

46. Section 27-1Mollusks • Can be a check on pollution levels, since some are filter-feeding bivalves • snails and other mollusks never seem to develop cancer; why is that? Scientists are interested in finding out!

47. Section 27-1Mollusks • Although beneficial in many ways, there are also some negative relationships with humans • land slugs and snails are plant eaters that do damage to crops • shipworms will damage wood ships- “termites of the sea”

48. Section 27-1Mollusks • Since many are filter-feeders, if we eat them, we are likely to get high concentrations of pathogens (things that cause disease), toxins, or pollutants that can result in sickness or even death

49. Section 27-2Annelids • OBJECTIVES: • Describe how annelids perform their essential life functions.

50. Section 27-2Annelids • OBJECTIVES: • List and give examples of three classes of annelids.