1. Worms and Mollusks
Biology I: Chapter 27

2. FLATWORMS

3. Flatworms Phylum Platyhelminthes Soft, flattened worms
Tissues and internal organs
Simplest animals to have:
3 embryonic germ layers
Bilateral symmetry (a right and a left)
Cephalization

4. Flatworms Acoelomate: flatworms are without a coelom
Coelom: fluid-filled body cavity lined with mesoderm
The digestive cavity is the only body cavity

5. Feeding Free-living flatworms Parasitic flatworms
Carnivores that feed on tiny aquatic animals
Scavengers that feed on recently dead animals
Parasitic flatworms
Feed on blood, tissue fluids, or pieces of cells within a host’s body (Example: tapeworm)

6. Respiration, Circulation, & Excretion
Rely on diffusion
Flame cells: remove excess water and metabolic wastes from the body

7. Response
Ganglia: group of nerve cells that controls the nervous system; in the head region
Eyespot

8. Movement
Cilia
Muscle cells

9. Reproduction: Sexually and Asexually
Free-living
Sexually: hermaphrodites
during sexual reproduction, two worms join in a pair, delivering sperm to each other
Asexually: fission

10. Reproduction: Sexually and Asexually
Parasitic
A complex life cycle including both sexual and asexual reproduction

11. Groups of Flatworms Turbellarians Flukes Tapeworms
Free-living; most live in marine or fresh water
Flukes
Parasitic; infect the internal organs of their host
Tapeworms
Long, flat, parasitic; adapted to life inside the intestines of their host

12. ROUNDWORMS

13. Roundworms Phylum Nematoda Slender, unsegmented worm Pseudocoelom
Digestive system with two openings: a mouth and an anus

14. Feeding Free-living roundworms
Carnivores that use grasping mouthparts and spines

15. Respiration, Circulation, & Excretion
Exchange gases and excrete metabolic waste through their body walls
No internal transport system
Depend on diffusion

16. Response Simple nervous systems, consisting of several ganglia
Run from the head to the tail
Nerves transmit sensory information and control movement

17. Movement Hydrostatic skeleton Aquatic roundworms move like snakes
Soil-dwelling roundworms push their way through by thrashing around

18. Reproduction Sexually Separate males and females
Internal fertilization
Male deposits sperm inside the female’s reproductive tract
Parasitic roundworms have complex life cycles involving two or three different hosts or organs within a single host

19. Roundworms and Human Disease
Trichinosis-causing worms
Adult worms live and mate in the intestines of their host (humans, pigs and other mammals)
Filarial worms
Found primarily in tropical regions of Asia, threadlike worms that live in the blood and lymph vessels of birds and mammals, including humans, transmitted by biting insects, causes elephantiasis

20. Roundworms and Human Disease
Ascarid worms
Serious parasite of humans and many other vertebrates, causes malnutrition; spread by eating vegetables or food that are not washed properly
Hookworms
Hatch outside the body of the host and develop in the soil, can enter a barefoot and travel through the bloodstream to the intestines

21. Research on C. elegans
Free-living roundworm Caenorhabditis elegans, C. elegans
Feeds on rotting vegetation
First multicellular animal whose DNA was fully sequenced
Helps understand genes and how eukaryotes became multicellular

22. ANNELIDS

23. Annelids True coelom that is lined Segmented bodies
Septa: internal walls between each segment
Setae: bristles that are attached to each segment; used in respiration

24. Form and Function in Annelids
Have complex organ systems
Segmented body

25. Feeding and Digestion Filter feeders to predators
Get their food using a pharynx
Crop: in earthworms; part of the digestive system in which food can be stored
Gizzard: in earthworms; part of the digestive system in which food is ground into smaller pieces

26. Circulation
Closed circulatory system: blood is contained within a network of blood vessels
Blood circulates through two major blood vessels that run from head to tail

27. Respiration Aquatic annelids: gills
Land-dwelling annelids: diffusion through their moist skin

28. Excretion Two kinds of waste
Digestive waste passes out through the anus at the end of the digestive tract
Nephridia: excretory organs that filter fluid in the coelom

29. Response
Well-developed nervous system consisting of a brain and several nerve cords
The sense organs are best developed in free-living marine annelids

30. Movement Hydrostatic skeleton
Longitudinal muscles and circular muscles
Moves by alternating contracting these two sets of muscles

31. Reproduction Sexually
Some use external fertilization or have separate sexes
Others, such as earthworms and leeches, are hermaphrodites
Exchange sperm
Clitellum: a band of thickened, specialized segments that secretes a mucus ring into which eggs and sperm are released and fertilization occurs
The ring slips off the body and form a protective cocoon for the worms that hatch a week later

32. Groups of Annelids Oligochaetes
Streamlined bodies and have relatively few setae compared to polychaetes, live in soil or fresh water
Leeches
External parasites that suck the blood and body fluids of their host
Polychaetes
Marine annelids that have paired, paddlelike appendages tipped with setae

33. Ecology of Annelids
Provide passageways for plant roots and water and allow the growth of beneficial, oxygen requiring soil bacteria
Important in the diet of many birds, moles, skunks, toads and snakes
In the sea they participate in a wide range of food chains

34. MOLLUSKS

35. Mollusks Phylum Mollusca Soft-bodied animals
Internal or external shell
Include snails, slugs, clams, squids and octopi
Trochophore: free-swimming larval stage of an aquatic mollusk

36. Form and Function in Mollusks
True coeloms
Have complex organ systems

37. Body Plan Foot: muscular part of a mollusk
Mantle: thin layer of tissue that covers most of a mollusk’s body

38. Body Plan
Shell: structure in mollusks made by glands in the mantle that secrete calcium carbonate
Visceral mass: area beneath the mantle of a mollusk that contains the internal organs

39. Feeding Herbivorous Carnivores Filter feeders Detritivores Parasites
Radula: flexible, tongue-shaped structure used to capture food by snails and slugs
Siphon: tube-like structure through which water enters and leaves the body, capturing plankton in the process

40. Respiration Gills inside their mantle cavity
Land snails respire using a mantle cavity lined with blood vessels
Typically live in moist places to keep this lining wet

41. Circulation
Open circulatory system: blood is pumped through vessels by a simple heart
Works well for slow-moving mollusks such as snails and clams (demands for oxygen are low)
Closed circulatory system: can transport blood through an animal’s body much more quickly

42. Excretion
Cells of the body release nitrogen-containing waste into the blood in the form of ammonia
Nephridia remove ammonia from the blood and release it out of the body

43. Response
Complexity of the nervous system varies greatly between mollusks
Clams and other two-shelled mollusk lead inactive lives simple nervous system

44. Response
Octopi and their relatives are active and intelligent predators  most highly developed nervous system of all invertebrates
Capable of complex behavior, such as opening a jar to get food inside

45. Movement Move in many different speeds
Snails secrete mucus and move slowly over the surface using a rippling motion of the foot
Octopus uses a form of jet propulsion, drawing water into its mantle and forcing it out the siphon

46. Reproduction Reproduce in many different ways
Snails and two-shelled mollusk reproduce sexually by external fertilization
Some mollusk are hermaphrodites

47. Groups of Mollusks Gastropods Bivalves Cephalopods
Shell-less or single-shelled mollusks that move by using a muscular foot located on the ventral side
Bivalves
Have two shells that are held together by one or two powerful muscles
Cephalopods
Soft-bodied mollusks in which the head is attached to a single foot; the foot is divided into tentacles or arms

48. Ecology of Mollusks
Feed on plants, prey on animals, and clean up their environment by filtering algae out of the water or by eating detritus
Filter-feeding bivalves can be used to monitor water quality
Serve as subjects of biological research