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Chapter 33

Chapter 33. Invertebrates. Figure 33.1. Overview: Life Without a Backbone Invertebrates Are animals that lack a backbone Account for 95% of known animal species. Porifera. Cnidaria. Chordata. Echinodermata. Other bilaterians (including Nematoda, Arthropoda, Mollusca, and Annelida).

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Chapter 33

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  1. Chapter 33 Invertebrates

  2. Figure 33.1 • Overview: Life Without a Backbone • Invertebrates • Are animals that lack a backbone • Account for 95% of known animal species

  3. Porifera Cnidaria Chordata Echinodermata Other bilaterians (including Nematoda, Arthropoda, Mollusca, and Annelida) Deuterostomia Bilateria Eumetazoa Ancestral colonial choanoflagellate Figure 33.2 • A review of animal phylogeny

  4. CNIDARIA (10,000 species) PORIFERA (5,500 species) A sponge A jelly PLACOZOA (1 species) KINORHYNCHA (150 species) 0.5 mm 250 µm A placozoan (LM) A kinorhynch (LM) ROTIFERA (1,800 species) PLATYHELMINTHES (20,000 species) A marine flatworm A rotifer (LM) PHORONIDA (20 species) ECTOPROCTA (4,500 species) Ectoprocts Phoronids • Exploring invertebrate diversity Figure 33.3

  5. BRACHIOPODA (335 species) NEMERTEA (900 species) A brachiopod A ribbon worm ACANTHOCEPHALA (1,100 species) CTENOPHORA (100 species) 5 mm An acanthocephalan A ctenophore, or comb jelly MOLLUSCA (93,000 species) ANNELIDA (16,500 species) An octopus A marine annelid LORICIFERA (10 species) PRIAPULA (16 species) 50 µm A priapulan A loriciferan (LM) Figure 33.3 • Exploring invertebrate diversity

  6. ARTHROPODA (1,000,000 + species) NEMATODA (25,000 species) A roundworm A scorpion (an arachnid) CYCLIOPHORA (1 species) TARDIGRADA (800 species) 100 µm 100 µm A cycliophoran (colorized SEM) Tardigrades (colorized SEM) HEMICHORDATA (85 species) ONYCHOPHORA (110 species) An onychophoran An acorn worm ECHINODERMATA (7,000 species) CHORDATA (52,000 species) Figure 33.3 A sea urchin A tunicate • Exploring invertebrate diversity

  7. Sponges are sessile and have a porous body and choanocytes • Sponges, phylum Porifera • Live in both fresh and marine waters • Lack true tissues and organs

  8. Choanocytes. The spongocoel is lined with feeding cells called choanocytes. By beating flagella, the choanocytes create a current that draws water in through the porocytes. 5 Flagellum Food particles in mucus Choanocyte Collar Azure vase sponge (Callyspongia plicifera) Osculum Spongocoel. Water passing through porocytes enters a cavity called the spongocoel. 4 Phagocytosis of food particles Amoebocyte Porocytes. Water enters the epidermis through channels formed by porocytes, doughnut-shaped cells that span the body wall. 3 The movement of the choanocyte flagella also draws water through its collar of fingerlike projections. Food particles are trapped in the mucus coating the projections, engulfed by phagocytosis, and either digested or transferred to amoebocytes. 6 Spicules Epidermis. The outer layer consists of tightly packed epidermal cells. 2 Water flow Amoebocyte. Amoebocytes transport nutrients to other cells of the sponge body and also produce materials for skeletal fibers (spicules). 7 Mesohyl. The wall of this simple sponge consists of two layers of cells separated by a gelatinous matrix, the mesohyl (“middle matter”). 1 • Sponges are suspension feeders • Capturing food particles suspended in the water that passes through their body Figure 33.4

  9. Choanocytes, flagellated collar cells • Generate a water current through the sponge and ingest suspended food • Most sponges are hermaphrodites • Meaning that each individual functions as both male and female

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

  11. Cnidarians • Have diversified into a wide range of both sessile and floating forms including jellies, corals, and hydras • But still exhibit a relatively simple diploblastic, radial body plan

  12. The basic body plan of a cnidarian • Is a sac with a central digestive compartment, the gastrovascular cavity • A single opening • Functions as both mouth and anus

  13. Medusa Mouth/anus Polyp Tentacle Gastrovascular cavity Gastrodermis Mesoglea Epidermis Body stalk Tentacle Mouth/anus Figure 33.5 • There are two variations on this body plan • The sessile polyp and the floating medusa

  14. Prey Tentacle “Trigger” Discharge Of thread Nematocyst Coiled thread Cnidocyte Figure 33.6 • Cnidarians are carnivores • That use tentacles to capture prey • The tentacles are armed with cnidocytes • Unique cells that function in defense and the capture of prey

  15. Table 33.1 • The phylum Cnidaria is divided into four major classes

  16. (d) Sea anemones and othermembers of class Anthozoaexist only as polyps. (b) Many species of jellies (classScyphozoa), including thespecies pictured here, are bioluminescent. The largest scyphozoans have tentaclesmore than 100 m long dangling from a bell-shaped body up to 2 m in diameter. (c) The sea wasp (Chironex fleckeri) is a member of class Cubozoa. Its poison,which can subdue fish andother large prey, is more potent than cobra venom. (a) These colonial polyps are members of class Hydrozoa. Figure 33.7a–d • Hydrozoa, Scyphozoa, Cubozoa, and Anthozoa

  17. Other polyps, specialized for reproduction, lack tentacles and produce tiny medusae by asexual budding. 3 Some of the colony’s polyps, equipped with tentacles, are specialized for feeding. The medusae swim off, grow, and reproduce sexually. 2 4 Reproductive polyp Feeding polyp A colony of interconnected polyps (inset, LM) results from asexual reproduction by budding. 1 Medusa bud MEIOSIS Gonad Medusa SEXUAL REPRODUCTION Sperm Egg ASEXUAL REPRODUCTION (BUDDING) Portion of a colony of polyps FERTILIZATION Zygote Developing polyp Mature polyp Planula (larva) Key Haploid (n) 1 mm Diploid (2n) Figure 33.8 Hydrozoans • Most hydrozoans • Alternate between polyp and medusa forms The planula eventually settles and develops into a new polyp. The zygote develops into a solid ciliated larva called a planula. 6 5

  18. Scyphozoans • In the class Scyphozoa • Jellies (medusae) are the prevalent form of the life cycle

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

  20. Anthozoans • Class Anthozoa includes the corals and sea anemones • Which occur only as polyps

  21. 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

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

  23. Table 33.2 • Flatworms are divided into four classes

  24. Figure 33.9 Turbellarian • Turbellarians • Are nearly all free-living and mostly marine

  25. Digestion is completed within the cells lining the gastro- vascular cavity, which has three branches, each with fine subbranches that pro- vide an extensive surface area. Pharynx. The mouth is at the tip of a muscular pharynx that extends from the animal’s ventral side. Digestive juices are spilled onto prey, and the pharynx sucks small pieces of food into the gastrovascular cavity, where digestion continues. Undigested wastes are egested through the mouth. Gastrovascular cavity Eyespots Ganglia. Located at the anterior end of the worm, near the main sources of sensory input, is a pair of ganglia, dense clusters of nerve cells. Ventral nerve cords. From the ganglia, a pair of ventral nerve cords runs the length of the body. Figure 33.10 • The best-known turbellarians, commonly called planarians • Have light-sensitive eyespots and centralized nerve nets

  26. Monogeneans and Trematode • Monogeneans and trematodes • Live as parasites in or on other animals • Parasitize a wide range of hosts

  27. Mature flukes live in the blood vessels of the human intestine. A female fluke fits into a groove running the length of the larger male’s body, as shown in the light micrograph at right. 1 Male Female 1 mm These larvae penetrate the skin and blood vessels of humans working in irrigated fields contaminated with infected human feces. 5 Blood flukes reproduce sexually in the human host. The fertilized eggs exit the host in feces. 2 The eggs develop in water into ciliated larvae. These larvae infect snails, the intermediate hosts. 3 Asexual reproduction within a snail results in another type of motile larva, which escapes from the snail host. 4 Snail host Figure 33.11 • Trematodes that parasitize humans • Spend part of their lives in snail hosts

  28. Most monogeneans • Are parasites of fish

  29. Proglottids with reproductive structures 200 µm Hooks Scolex Sucker Figure 33.12 Tapeworm • Tapeworms • Are also parasitic and lack a digestive system

  30. Rotifers • Rotifers, phylum Rotifera • Are tiny animals that inhabit fresh water, the ocean, and damp soil

  31. 0.1 mm Figure 33.13 • Rotifers are smaller than many protists • But are truly multicellular and have specialized organ systems

  32. 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 more females from unfertilized eggs

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

  34. Lophophore Ectoprocts, such as this sea mat (Membranipora membranacea), are colonial lophophorates. (a) Figure 33.14a • Ectoprocts • Are colonial animals that superficially resemble plants

  35. Lophophore (b) In phoronids such as Phoronis hippocrepia, the lophophore and mouth are at one end of an elongated trunk. Figure 33.14b • Phoronids • Are tube-dwelling marine worms ranging from 1 mm to 50 cm in length

  36. Lophophore Brachiopods have a hinged shell. The two parts of the shell are dorsal and ventral. (c) Figure 33.14c • 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

  37. Figure 33.15 Nemerteans • Members of phylum Nemertea • Are commonly called proboscis worms or ribbon worms

  38. The nemerteans unique proboscis • Is used for defense and prey capture • 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

  39. Concept 33.4: Molluscs have a muscular foot, a visceral mass, and a mantle • Phylum Mollusca • Includes snails and slugs, oysters and clams, and octopuses and squids • Most molluscs are marine • Though some inhabit fresh water and some are terrestrial • Molluscs are soft-bodied animals • But most are protected by a hard shell

  40. All molluscs have a similar body plan with three main parts • A muscular foot • A visceral mass • A mantle

  41. Heart. Most molluscs have an open circulatory system. The dorsally located heart pumps circulatory fluid called hemolymph through arteries into sinuses (body spaces). The organs of the mollusc are thus continually bathed in hemolymph. Nephridium. Excretory organs called nephridia remove metabolic wastes from the hemolymph. The long digestive tract is coiled in the visceral mass. Visceral mass Coelom Intestine Gonads Mantle Stomach Radula. The mouth region in many mollusc species contains a rasp-like feeding organ called a radula. This belt of backward- curved teeth slides back and forth, scraping and scooping like a backhoe. Mantle cavity Shell Mouth Radula Anus The nervous system consists of a nerve ring around the esophagus, from which nerve cords extend. Gill Nerve cords Foot Mouth Esophagus Figure 33.16

  42. Most molluscs have separate sexes • With gonads located in the visceral mass • The life cycle of many molluscs • Includes a ciliated larval stage called a trochophore

  43. Table 33.3 • There are four major classes of molluscs

  44. Figure 33.17 Chitons • Class Polyplacophora is composed of the chitons • Oval-shaped marine animals encased in an armor of eight dorsal plates

  45. (a) A land snail A sea slug. Nudibranchs, or sea slugs, lost their shell during their evolution. (b) Figure 33.18a, b Gastropods • About three-quarters of all living species of molluscs • Belong to class Gastropoda

  46. Most gastropods • Are marine, but there are also many freshwater and terrestrial species • Possess a single, spiraled shell • Slugs lack a shell • Or have a reduced shell

  47. Stomach Mantle cavity Intestine Anus Mouth Figure 33.19 • The most distinctive characteristic of this class • Is a developmental process known as torsion, which causes the animal’s anus and mantle to end up above its head

  48. Figure 33.20 Bivalves • Molluscs of class Bivalvia • Include many species of clams, oysters, mussels, and scallops • Have a shell divided into two halves

  49. Hinge area Coelom Gut Mantle Heart Shell Adductor muscle Mouth Anus Excurrent siphon Palp Water flow Foot Incurrent siphon Mantle cavity Gill Figure 33.21 • The mantle cavity of a bivalve • Contains gills that are used for feeding as well as gas exchange

  50. Cephalopods • Class Cephalopoda includes squids and octopuses • Carnivores with beak-like jaws surrounded by tentacles of their modified foot

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