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Chapter 33

Chapter 33. Invertebrates. Overview: Life Without a Backbone. Invertebrates are animals that lack a backbone They account for 95% of known animal species. LE 33-2. Cnidaria. Echinodermata. Chordata. Porifera. Other bilaterians (including Nematoda, Arthropoda, Mollusca, and Annelida).

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Chapter 33

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  1. Chapter 33 Invertebrates

  2. Overview: Life Without a Backbone • Invertebrates are animals that lack a backbone • They account for 95% of known animal species

  3. LE 33-2 Cnidaria Echinodermata Chordata Porifera Other bilaterians (including Nematoda, Arthropoda, Mollusca, and Annelida) Deuterostomia Bilateria Eumetazoa Ancestral colonial choanoflagellate

  4. LE 33-3a A jelly A sponge 0.5 mm 250 µm A placozoan (LM) A kinorhynch (LM) A rotifer (LM) A marine flatworm Ectoprocts Phoronids

  5. LE 33-3b A ribbon worm A brachiopod 5 mm A ctenophore, or comb jelly An acanthocephalan An octopus A marine annelid 50 µm A priapulan A loriciferan (LM)

  6. LE 33-3c A roundworm A scorpion (an arachid) 100 µm 100 µm Tardigrades (colorized SEM) A cycliophoran (colorized SEM) An acorn worm An onychophoran A sea urchin A tunicate

  7. Concept 33.1: Sponges are sessile and have a porous body and choanocytes • Sponges, phylum Porifera, live in both fresh and marine waters • Sponges lack true tissues and organs

  8. Sponges are suspension feeders, capturing food particles suspended in the water that passes through their body

  9. LE 33-4 Food particles in mucus Flagellum Choanocyte Choanocytes Collar Osculum Azure vase sponge (Callyspongia plicifera) Spongocoel Phagocytosis of food particles Amoebocyte Porocytes Spicules Epidermis Water flow Amoebocyte Mesohyl

  10. Choanocytes, flagellated collar cells, generate a water current through the sponge and ingest suspended food • Most sponges are hermaphrodites: Each individual functions as both male and female

  11. Concept 33.2: Cnidarians have radial symmetry, a gastrovascular cavity, and cnidocytes • All animals except sponges belong to the clade Eumetazoa, animals with true tissues • Phylum Cnidaria is one of the oldest groups in this clade

  12. Cnidarians have diversified into a wide range of both sessile and floating forms including jellies, corals, and hydras • They exhibit a relatively simple diploblastic, radial body plan

  13. The basic body plan of a cnidarian is a sac with a central digestive compartment, the gastrovascular cavity • A single opening functions as mouth and anus • There are two variations on the body plan: the sessile polyp and floating medusa Video: Hydra Eating Daphnia (time lapse)

  14. LE 33-5 Mouth/anus Tentacle Polyp Medusa Gastrovascular cavity Gastrodermis Mesoglea Body stalk Epidermis Tentacle Mouth/anus

  15. Cnidarians are carnivores that use tentacles to capture prey • The tentacles are armed with cnidocytes, unique cells that function in defense and capture of prey Video: Hydra Budding Video: Hydra Releasing Sperm

  16. LE 33-6 Prey Tentacle “Trigger” Discharge of thread Nematocyst Coiled thread Cnidocyte

  17. Phylum Cnidaria is divided into four major classes: • Hydrozoa • Scyphozoa • Cubozoa • Anthozoa

  18. LE 33-7 Scyphozoans (jellies) Cubozoan (sea wasp) Anthozoan (sea anemone) Hydrozoans

  19. Video: Jelly Swimming Video: Thimble Jellies Video: Clownfish and Anemone Video: Coral Reef

  20. Hydrozoans • Most hydrozoans alternate between polyp and medusa forms

  21. LE 33-8–3 Reproductive polyp Feeding polyp Medusa bud MEIOSIS Gonad Medusa Sperm Egg SEXUAL REPRODUCTION ASEXUAL REPRODUCTION (BUDDING) Portion of a colony of polyps FERTILIZATION Zygote Developing polyp Mature polyp Planula (larva) Key Haploid (n) 1 mm Diploid (2n)

  22. Scyphozoans • In the class Scyphozoa, jellies (medusae) are the prevalent form of the life cycle

  23. Cubozoans • In the class Cubozoa, which includes box jellies and sea wasps, the medusa is box-shaped and has complex eyes

  24. Anthozoans • Class Anthozoa includes the corals and sea anemones, which occur only as polyps

  25. Concept 33.3: Most animals have bilateral symmetry • The vast majority of animal species belong to the clade Bilateria, which consists of animals with bilateral symmetry and triploblastic development

  26. Flatworms • Members of phylum Platyhelminthes live in marine, freshwater, and damp terrestrial habitats • They are flattened dorsoventrally and have a gastrovascular cavity • Although flatworms undergo triploblastic development, they are acoelomates

  27. Flatworms are divided into four classes: • Turbellaria (mostly free-living flatworms) • Monogenea (monogeneans) • Trematoda (trematodes, or flukes) • Cestoda (tapworms)

  28. Turbellarians • Turbellarians are nearly all free-living and mostly marine • The best-known turbellarians are commonly called planarians

  29. Planarians have light-sensitive eyespots and centralized nerve nets • The planarian nervous system is more complex and centralized than the nerve nets of cnidarians

  30. LE 33-10 Pharynx Gastrovascular cavity Eyespots Ganglia Ventral nerve cords

  31. Monogeneans and Trematodes • Monogeneans and trematodes live as parasites in or on other animals • They parasitize a wide range of hosts • Trematodes that parasitize humans spend part of their lives in snail hosts

  32. LE 33-11 Mature flukes live in the blood vessels of the human intestine Male Female 1 mm Larvae penetrate skin and blood vessels of humans. Blood flukes reproduce sexually in the human host. Fertilized eggs exit host in feces. Eggs develop in water into ciliated larvae. Larvae infect snails. Asexual reproduction within snail results in another type of motile larva. Snail host

  33. Most monogeneans are parasites of fish

  34. Tapeworms • Tapeworms are also parasitic and lack a digestive system

  35. LE 33-12 Proglottids with reproductive structures 200 µm Scolex Hooks Sucker

  36. Rotifers • Rotifers, phylum Rotifera, are tiny animals that inhabit fresh water, the ocean, and damp soil • Rotifers are smaller than many protists but are truly multicellular and have specialized organ systems Video: Rotifer

  37. LE 33-13 0.1 mm

  38. Rotifers have an alimentary canal: a digestive tube with a separate mouth and anus that lies within a fluid-filled pseudocoelom • Rotifers reproduce by parthenogenesis, in which females produce offspring from unfertilized eggs

  39. Lophophorates: Ectoprocts, Phoronids, and Brachiopods • Lophophorates have a lophophore, a horseshoe-shaped, suspension-feeding organ with ciliated tentacles

  40. Ectoprocts are colonial animals that superficially resemble plants

  41. LE 33-14 Lophophore Lophophore Ectoprocts Phoronids Brachiopods

  42. Phoronids are tube-dwelling marine worms ranging from 1 mm to 50 cm in length

  43. Brachiopods superficially resemble clams and other hinge-shelled molluscs, but the two halves of the shell are dorsal and ventral rather than lateral, as in clams

  44. Nemerteans • Members of phylum Nemertea are commonly called proboscis worms or ribbon worms

  45. The nemerteans’ unique proboscis is used for defense and prey capture and is extended by a fluid-filled sac • Nemerteans also have a closed circulatory system, in which the blood is contained in vessels distinct from fluid in the body cavity

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