1. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Chapter 33 Invertebrates

2. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Overview: Invertebrates – Are animals that lack a backbone – Account for 95% of known animal species Figure 33.1 Christmas Tree WormChristmas Tree Worm

3. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings A review of animal phylogeny Ancestral colonial choanoflagellate Eumetazoa Bilateria Deuterostomia Porifera Cnidaria Other bilaterians (including Nematoda, Arthropoda, Mollusca, and Annelida) Echinodermata Chordata Figure 33.2

4. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Exploring invertebrate diversity PORIFERA (5,500 species) A sponge CNIDARIA (10,000 species) A jelly PLACOZOA (1 species)KINORHYNCHA (150 species) 0.5 mm A placozoan (LM) A kinorhynch (LM) 250 µm PLATYHELMINTHES (20,000 species) ROTIFERA (1,800 species) A marine flatworm A rotifer (LM) ECTOPROCTA (4,500 species) PHORONIDA (20 species) Ectoprocts Phoronids Figure 33.3

5. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Exploring invertebrate diversity BRACHIOPODA (335 species) NEMERTEA (900 species) A brachiopod A ribbon worm ACANTHOCEPHALA (1,100 species) CTENOPHORA (100 species) An acanthocephalanA ctenophore, or comb jelly MOLLUSCA (93,000 species)ANNELIDA (16,500 species) An octopus A marine annelid LORICIFERA (10 species) PRIAPULA (16 species) 5 mm 50 µm A loriciferan (LM) A priapulan Figure 33.3

6. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Exploring invertebrate diversity NEMATODA (25,000 species) ARTHROPODA (1,000,000 + species)A roundworm A scorpion (an arachnid) CYCLIOPHORA (1 species) TARDIGRADA (800 species) 100 µm A cycliophoran (colorized SEM)Tardigrades (colorized SEM) ONYCHOPHORA (110 species) HEMICHORDATA (85 species) An onychophoran An acorn worm ECHINODERMATA (7,000 species)CHORDATA (52,000 species) A sea urchin A tunicate Figure 33.3

7. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Concept 33.1: Sponges, phylum Porifera, are sessile and have a porous body and choanocytes Sponges – Live in both fresh and marine waters – Lack true tissues and organs

8. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Sponges are suspension feeders – Capturing food particles suspended in the water that passes through their body Azure vase sponge (Callyspongia plicifera) Osculum Spicules Water flow Flagellum Collar Food particles in mucus Choanocyte Phagocytosis of food particles Amoebocyte 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. Spongocoel. Water passing through porocytes enters a cavity called the spongocoel. Porocytes. Water enters the epidermis through channels formed by porocytes, doughnut-shaped cells that span the body wall. Epidermis. The outer layer consists of tightly packed epidermal cells. Mesohyl. The wall of this simple sponge consists of two layers of cells separated by a gelatinous matrix, the mesohyl (“middle matter”). 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. Amoebocyte. Amoebocytes transport nutrients to other cells of the sponge body and also produce materials for skeletal fibers (spicules). 5 6 7 4 3 2 1 Figure 33.4

9. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Concept 33.2: Cnidarians 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. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings There are two variations on this body plan – The sessile polyp and the floating medusa Mouth/anus Tentacle Gastrovascular cavity Gastrodermis Mesoglea Epidermis Tentacle Body stalk Mouth/anus Medusa Polyp Figure 33.5

14. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Tentacle “Trigger” Nematocyst Coiled thread Discharge Of thread Cnidocyte Prey 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. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The phylum Cnidaria is divided into four major classes – Hydrozoa, Scyphozoa, Cubozoa, and Anthozoa (a) These colonial polyps are members of class Hydrozoa. (b) Many species of jellies (class Scyphozoa), including the species pictured here, are bioluminescent. The largest scyphozoans have tentacles more 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 and other large prey, is more potent than cobra venom. (d) Sea anemones and other members of class Anthozoa exist only as polyps. Figure 33.7a–d

16. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Hydrozoans Most hydrozoans – Alternate between polyp and medusa forms Feeding polyp Reproductive polyp Medusa bud ASEXUAL REPRODUCTION (BUDDING) Gonad Medusa MEIOSIS FERTILIZATION SEXUAL REPRODUCTION Egg Sperm Developing polyp Portion of a colony of polyps Mature polyp Planula (larva) Key Haploid (n) Diploid (2n) 1 mm Zygote Figure 33.8 A colony of interconnected polyps (inset, LM) results from asexual reproduction by budding. 1 Some of the colony’s polyps, equipped with tentacles, are specialized for feeding. 2 Other polyps, specialized for reproduction, lack tentacles and produce tiny medusae by asexual budding. 3 The medusae swim off, grow, and reproduce sexually. 4 The zygote develops into a solid ciliated larva called a planula. 5 The planula eventually settles and develops into a new polyp. 6

17. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Scyphozoans In the class Scyphozoa, – Jellies (medusae) are the prevalent form of the life cycle

18. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Cubozoans In the class Cubozoa, which includes box jellies and sea wasps – The medusa is box-shaped and has complex eyes

19. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Anthozoans Class Anthozoa includes the corals and sea anemones – Which occur only as polyps

20. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Concept 33.3: PlatyhelminthesPlatyhelminthes The vast majority of animal species belong to the clade Bilateria – Which consists of animals with bilateral symmetry and triploblastic development

21. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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

22. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Flatworms are divided into four classes Table 33.2

23. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Turbellarian Turbellarians – Are nearly all free-living and mostly marine Figure 33.9

24. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The best-known turbellarians, commonly called planarians – Have light-sensitive eyespots and centralized nerve nets 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. 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. Undigested wastes are egested through the mouth. 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. Gastrovascular cavity Eyespots Figure 33.10

25. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Monogeneans and Trematode Monogeneans and trematodes – Live as parasites in or on other animals – Parasitize a wide range of hosts Most monogeneans are parasites of fish

26. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Trematodes that parasitize humans spend part of their lives in snail hosts These larvae penetrate the skin and blood vessels of humans working in irrigated fields contaminated with infected human feces. Asexual reproduction within a snail results in another type of motile larva, which escapes from the snail host. Blood flukes reproduce sexually in the human host. The fertilized eggs exit the host in feces. The eggs develop in water into ciliated larvae. These larvae infect snails, the intermediate hosts. Snail host 1 mm Female Male 5 2 3 4 Figure 33.11 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

27. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Cestoda Tapeworms – Are also parasitic and lack a digestive system Proglottids with reproductive structures 200 µm Hooks Sucker Scolex Figure 33.12

28. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Concept 33.4: Mollusca Phylum Mollusca – Includes snails and slugs, oysters and clams, and octopuses and squids Molluscs have a muscular foot, a visceral mass, and a mantle 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

29. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings All molluscs have a similar body plan with three main parts – A muscular foot – A visceral mass – A mantle

30. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Mollusc anatomy Visceral mass Mantle Foot Coelom Intestine Gonads Mantle cavity Anus Gill Nerve cords Esophagus Stomach Shell Radula Mouth Nephridium. Excretory organs called nephridia remove metabolic wastes from the hemolymph. 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. The long digestive tract is coiled in the visceral mass. 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. The nervous system consists of a nerve ring around the esophagus, from which nerve cords extend. Figure 33.16

31. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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

32. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Table 33.3 There are four major classes of molluscs

33. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Chitons Class Polyplacophora is composed of the chitons – Oval-shaped marine animals encased in an armor of eight dorsal plates Figure 33.17

34. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Gastropods About three-quarters of all living species of molluscs belong to class Gastropoda A land snail (a) A sea slug. Nudibranchs, or sea slugs, lost their shell during their evolution. (b) Figure 33.18a, b

35. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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

36. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 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 Anus Mantle cavity Stomach Intestine Mouth Figure 33.19

37. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Bivalves Molluscs of class Bivalvia – Include many species of clams, oysters, mussels, and scallops – Have a shell divided into two halves Figure 33.20

38. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Anatomy of a bivalve Hinge area Gut Coelom Heart Adductor muscle Anus Excurrent siphon Water flow Incurrent siphon Gill Mantle cavity Foot Palp Mouth Shell Mantle Figure 33.21

39. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Cephalopods Class Cephalopoda includes squids and octopuses – Carnivores with beak-like jaws surrounded by tentacles of their modified foot

40. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Many octopuses – Creep along the sea floor in search of prey – Ambush prey from hiding places Figure 33.22a (a) Octopuses are considered among the most intelligent invertebrates.

41. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Squids use their siphon – To fire a jet of water, which allows them to swim very quickly Figure 33.22b (b) Squids are speedy carnivores with beaklike jaws and well-developed eyes.

42. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Concept 33.5: Annelida Annelids are segmented worms – They have bodies composed of a series of fused rings

43. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The phylum Annelida is divided into three classes Table 33.4

44. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Oligochaetes Oligochaetes (class Oligochaeta) – Are named for their relatively sparse chaetae, or bristles made of chitin – Include the earthworms and a variety of aquatic speciesearthworms

45. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Earthworms eat their way through the soil, extracting nutrients as the soil moves through the alimentary canal – Which creates pores for water and air flow, and root growth, making soils conducive to plant growth

46. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Anatomy of an earthworm Mouth Subpharyngeal ganglion Pharynx Esophagus Crop Gizzard Intestine Metanephridium Ventral vessel Nerve cords Nephrostome Intestine Dorsal vessel Longitudinal muscle Circular muscle Epidermis Cuticle Septum Anus Chaetae Giant Australian earthworm Clitellum Table 33.23

47. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Polychaetes Members of class Polychaeta – Possess paddlelike parapodia that function as gills and aid in locomotion Parapodia Figure 33.24

48. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Leeches Members of class Hirudinea – Are blood-sucking parasites, such as leeches Figure 33.25

49. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Concept 33.6: Nematoda Nematodes are nonsegmented pseudocoelomates covered by a tough cuticle Nematodes, or roundworms – Are found in most aquatic habitats, in the soil, in moist tissues of plants, and in the body fluids and tissues of animals

50. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Some species of nematodes – Are important parasites of plants and animals 50 µm Encysted juveniles Muscle tissue Figure 33.27

51. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Concept 33.7: Arthropoda Arthropods are segmented coelomates that have an exoskeleton and jointed appendages Two out of every three known species of animals are arthropods Members of the phylum Arthropoda are found in nearly all habitats of the biosphere

52. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings General Characteristics of Arthropods The diversity and success of arthropods – Are largely related to their segmentation exoskeleton jointed appendages

53. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Early arthropods, such as trilobites – Showed little variation from segment to segment Figure 33.28

54. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings As arthropods evolved – The segments fused, and the appendages became more specialized Antennae (sensory reception) Head Thorax Swimming appendages Walking legs Mouthparts (feeding) Pincer (defense) Abdomen Cephalothorax Figure 33.29

55. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The body of an arthropod – Is completely covered by the cuticle, an exoskeleton made of chitin When an arthropod grows – It molts its exoskeleton in a process called ecdysis

56. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Arthropods have an open circulatory system – In which fluid called hemolymph is circulated into the spaces surrounding the tissues and organs A variety of organs specialized for gas exchange – Have evolved in arthropods

57. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Concept 33.8: Echinodermata and Chordata Chordates and echinoderms share characteristics of deuterostomes – Radial cleavage – Development of the coelom from the archenteron – Formation of the mouth at the end of the embryo opposite the blastopore

58. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Echinoderms Sea stars and most other echinoderms – Are slow-moving or sessile marine animals A thin, bumpy or spiny skin – Covers an endoskeleton of hard calcareous plates

59. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Unique to echinoderms is a water vascular system – A network of hydraulic canals branching into tube feet that function in locomotion, feeding, and gas exchange Ring canal Tube feet Madreporite. Water can flow in or out of the water vascular system into the surrounding water through the madreporite. Branching from each radial canal are hundreds of hollow, muscular tube feet filled with fluid. Movement occurs by sequential contraction and relaxation of the tube feet. Radial canal. The water vascular system consists of a ring canal in the central disk and five radial canals, each running in a groove down the entire length of an arm. Central disk Figure 33.39 A Sea Star

60. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Brittle Stars Brittle stars have a distinct central disk – And long, flexible arms (b) A brittle star (class Ophiuroidea) Figure 33.40b

61. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Sea Urchins and Sand Dollars Sea urchins and sand dollars have no arms – But they do have five rows of tube feet that function in movement (c) A sea urchin Figure 33.40c

62. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Selected Animal Phyla Table 33.7