Animals: The Invertebrates

1. Animals: The Invertebrates Chapter 23

2. Characteristics of Animals • Multicelled heterotrophic eukaryotes that ingest or parasitize other organisms. • Require oxygen for aerobic respiration • Reproduce sexually, and perhaps asexually • Motile at some stage • Develop from embryos • Almost all have tissues, organs and organ systems. • Animals originate during late precambrian.

3. Major Animal Phyla

4. Symmetry Radial Bilateral

5. The Gut • Region where food is digested and then absorbed • Saclike gut • One opening for taking in food and expelling waste • Complete digestive system • Opening at both ends; mouth and anus

6. Body Cavities - Acoelomate epidermis gut cavity no body cavity; region between gut and body wall packed with organs

7. Body Cavities - Pseudocoel epidermis gut cavity unlined body cavity (pseudocoel) around gut

8. Body Cavities - Coelom gut cavity peritoneum lined body cavity (coelom)

9. Segmentation • Repeating series of body units • Units may or may not be similar to one another • Earthworms - segments appear similar • Insects - segments may be fused and/or have specialized functions

10. Animal Origins • Originated during the Precambrian (1.2 billion - 670 million years ago) • From what? Two hypotheses: • Multinucleated ciliate became compartmentalized • Cells in a colonial flagellate became specialized

11. Phylum Placozoa • One living species, Tricoplax adherens • Simplest known animal • Two-layer body, 3 mm across

12. Sponges - Phylum Porifera • No symmetry • No tissues • No organs • Reproduce sexually • Microscopic swimming-larval stage

13. Sponge Structure water out glasslike structural elements amoeboid cell pore central cavity semifluid matrix flattened surface cells water in flagellum microvilli nucleus

14. Phylum Cnidaria • Only animals that produce nematocysts • Nerve net • Hydrostatic skeleton • Saclike gut

15. Cnidarian Diversity • Scyphozoans • Jellyfish • Anthozoans • Sea anemones • Corals • Hydrozoans

16. Two Main Body Plans polyp outer epithelium (epidermis) mesoglea (matrix) medusa inner epithelium (gastrodermis)

17. Obelia Life Cycle (Hydrozoan) male medusa female medusa reproductive polyp sperm ovum zygote feeding polyp polyp forming planula

18. Flatworms: Phylum Platyhelminthes • Acoelomate, bilateral, cephalized animals • All have simple or complex organ systems • Most are hermaphrodites

19. Three Classes • Turbellarians (Turbellaria) • Flukes (Trematoda) • Tapeworms (Cestoda)

20. Planarian Organ Systems brain nerve cord oviduct genital pore ovary testis penis

21. Planarian Organ Systems flame cell nucleus pharynx cilia protonephridia fluid filters through membrane folds opening of tubule at body surface flame cell

22. Flukes: Class Trematoda • Parasitic worms • Complicated life cycle • Larval stage infects a mollusk • Adult infects a vertebrate Worms mate in human host Larvae bore into human skin Larvae form, leave snail Fertilized egg Asexual reproduction in intermediate host Cilated larva Southeast Asian blood fluke

23. Tapeworms: Class Cestoda Definitive host Larvae encysted in muscle tissue Scolex attaches to host intestinal wall Intermediate host Mature proglottid with fertilized eggs

24. Roundworms (Nematoda) • False coelom • Complete digestive system pharynx intestine eggs in uterus gonad anus false coelom muscularized body wall

25. Two Coelomate Lineages Deuterostomes • Echinoderms • Chordates Protostomes • Mollusks • Annelids • Arthropods

26. Cleavage Patterns Protostome embryo (spiral cleavage) Deuterostome embryo (radial cleavage)

27. First Opening in Embryo pouch will form mesoderm around coelom protostome developing gut coelom solid mass of mesoderm deuterostome developing gut

28. Mollusks: Phylum Mollusca • Bilateral, soft-bodied coelomate • Most have a shell or reduced version of one • Mantle drapes over body and secretes shell • Most have a fleshy foot • Many have a radula for shredding food

29. Molluscan Diversity • Gastropods • Chitons • Bivalves • Cephalopods

30. Torsion • Twisting of body parts during larval development • Occurs only in gastropods • Before torsion: head faces forward and anus faces backward • After torsion: anus is positioned over head

31. Body Plan of a Snail heart mantle cavity mouth anus gill gill anus mantle digestive gland foot radula

32. Body Plan of a Clam left mantle mouth retractor muscle retractor muscle foot shell left gill palps

33. Cephalopods • Only the nautilus retains external shell • Other cephalopods are streamlined, active swimmers • All move by jet propulsion • Water is forced out of mantle cavity through a funnel-shaped siphon • Have large brains relative to body size

34. Cuttlefish Body Plan • Closed circulatory system with heart and accessory heart digestive gland stomach radula brain shell siphon reproductive organ accessory heart anus heart gill

35. Annelids: Phylum Annelida • Segmented, coelomate worms • Class Polychaeta • Class Oligochaeta • Class Hirudinea

36. Polychaetes • Most are marine • Bristles extend from paired, fleshy parapods on each segment • Head end is specialized

37. Leeches - Class Hirudinea • Predators and parasites • Less obvious body segmentation • Most have sharp jaws

38. Earthworm - An Oligochaete • No parapodia, few bristles per segment Nerve cord Dorsal blood vessel Circular muscle Coelom Longitudinal muscle Nephridium Seta (retracted) Nerve cord

39. Earthworm Circulatory System Hearts

40. Earthworm Digestive System Coelomic chambers Crop Gizzard Esophagus Pharynx Mouth

41. Earthworm Nervous System Brain Nerve cord

42. Arthropods: Phylum Arthropoda • The phylum with the greatest number of species • Four lineages: • Trilobites (all extinct) • Chelicerates (spiders, mites, scorpions) • Crustaceans (crabs, shrimps, barnacles) • Uniramians (insects, centipedes, millipedes)

43. Adaptations for Success • Hardened exoskeleton • Jointed appendages • Fused and modified segments • Respiratory structures • Specialized sensory structures • Division of labor

44. Chelicerates • Originated in seas • A few are still marine: horseshoe crabs, sea spiders • The arachnids are all terrestrial Spiders Mites Scorpions Chiggers “Daddy longlegs” Ticks

45. Body Plan of a Spider Malpighian tubule heart brain anus book lung silk gland pedipalp chelicera

46. Crustaceans • Copepods • Crayfish • Barnacles • Lobsters • Shrimps • Crabs • Isopods (pillbugs) • Most are marine, some freshwater, a few terrestrial • Head has two pairs of antenna, three pairs of food-handling appendages

47. Lobster Body Plan one of two eyes segments of abdomen fused segments of cephalothorax antennae (two pairs) food-handling appendages (three pairs) swimmerets tail fin first leg five walking legs (five pairs total)

48. Crab Life Cycle Larval and juvenile stages molt repeatedly and grow in size

49. Millipedes and Centipedes • Segmented bodies with many legs • Millipedes • Two pairs of legs per “segment” • Scavengers • Centipedes • Flattened with one pairs of legs per segment • Predators

50. Insect Body Plan • Thorax usually has three pairs of legs and one or two pairs of wings • Abdomen contains most internal organs and specialized structure for reproduction • Three-part gut • Malpighian tubules attach to midgut and serve in elimination of wastes