1. 14-1 CHAPTER 14 Flat Worms, Mesozoans and Ribbonworms: Phylum Acoelomorpha Phylum Mesozoa Flat Worms, Mesozoans and Ribbonworms: Phylum Acoelomorpha Phylum Mesozoa

2. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 14-2 General Features General Features Animals that actively seek food, shelter, home sites, and mates require a different set of strategies and body organization than radially symmetrical sessile organisms Animals that actively seek food, shelter, home sites, and mates require a different set of strategies and body organization than radially symmetrical sessile organisms Two major evolutionary advances Two major evolutionary advances Cephalization Cephalization Concentrating sense organs in the head region Concentrating sense organs in the head region Primary bilateral symmetry Primary bilateral symmetry Body can be divided along only 1 plane of symmetry to yield 2 mirror images of each other Body can be divided along only 1 plane of symmetry to yield 2 mirror images of each other Active, directed movement most efficient with an elongated body form with anterior (head), posterior (head), dorsal, and ventral sides Active, directed movement most efficient with an elongated body form with anterior (head), posterior (head), dorsal, and ventral sides

3. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 14-3 General Features Position and Biological Contributions Simplest animals with primary bilateral symmetry Simplest animals with primary bilateral symmetry Mesoderm well-defined Mesoderm well-defined Triploblastic Triploblastic Mesozoans Mesozoans No clearly defined body layers No clearly defined body layers Development does not include gastrulation Development does not include gastrulation Highly specialized parasites Highly specialized parasites Some argue this group were derived from complex free-living organisms Some argue this group were derived from complex free-living organisms

4. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 14-4 General Features Acoelomates Acoelomates Typical acoelomates have only one internal space, the digestive cavity Typical acoelomates have only one internal space, the digestive cavity Region between the epidermis and digestive cavity is filled with parenchyma Region between the epidermis and digestive cavity is filled with parenchyma Some members of Acoelomorpha are atypical acoelomates: No digestive cavity Some members of Acoelomorpha are atypical acoelomates: No digestive cavity

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6. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 14-6 General Features Developmental character suites define two metazoan clades: Protostomia and Deuterostomia Developmental character suites define two metazoan clades: Protostomia and Deuterostomia Protostomes Protostomes Spiral or centrolecithal cleavage Spiral or centrolecithal cleavage Development is mosaic Development is mosaic Embryonic blastopore becomes the mouth Embryonic blastopore becomes the mouth Coelom forms by schizocoely Coelom forms by schizocoely

7. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 14-7 Deuterostomes Deuterostomes Radial cleavage Radial cleavage Development is regulative Development is regulative Blastopore becomes the anus Blastopore becomes the anus Coelome forms by enterocoely Coelome forms by enterocoely Platyhelminth: acoelomate protostomes Platyhelminth: acoelomate protostomes Nemertea: coelomate protostomes Nemertea: coelomate protostomes General Features

8. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 14-8 Characteristics Small flat worms less than 5 mm in length Small flat worms less than 5 mm in length Typically live in marine sediments; few are pelagic Typically live in marine sediments; few are pelagic Some species live in brackish water Some species live in brackish water Most symbiotic but some parasitic Most symbiotic but some parasitic Group contains ~350 species Group contains ~350 species Members were formerly in Class Turbellaria within phylum Platyhelminthes Members were formerly in Class Turbellaria within phylum Platyhelminthes Have a cellular ciliated epidermis Have a cellular ciliated epidermis Parenchyma layer contains small amount of ECM and circular, longitudinal, and diagonal muscles Parenchyma layer contains small amount of ECM and circular, longitudinal, and diagonal muscles Phylum Acoelomorpha

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10. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 14-10 Digestion and Nutrition Some have digestive system from a mouth to a tube-like pharynx followed by a sack-like gut Some have digestive system from a mouth to a tube-like pharynx followed by a sack-like gut No anus No anus In many acoels, the gut and pharynx are absent In many acoels, the gut and pharynx are absent Mouth leads into either an endodermally derived mass of cells or syncytial mass Mouth leads into either an endodermally derived mass of cells or syncytial mass Phagocytotic cells digest food intracellularly when food is passed into temporary spaces Phagocytotic cells digest food intracellularly when food is passed into temporary spaces Phylum Acoelomorpha

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12. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 14-12 Reproduction Monoecious Monoecious Female produces yolk-filled eggs Female produces yolk-filled eggs Endolecithal eggs Endolecithal eggs Following fertilization Following fertilization Some or all cleavage events produce a duet-spiral pattern of new cells Some or all cleavage events produce a duet-spiral pattern of new cells Phylum Acoelomorpha Phylum Acoelomorpha

13. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 14-13 Nervous System Other defining features proposed for acoelomorphs Other defining features proposed for acoelomorphs Biochemical (patterns of neurotransmitters) Biochemical (patterns of neurotransmitters) Cellular ultrastructure such as formation of a network of interconnecting rootlets from epidermal cilia Cellular ultrastructure such as formation of a network of interconnecting rootlets from epidermal cilia Acoelomorphs lack a “true” brain Acoelomorphs lack a “true” brain Have a radial arrangement of nerves instead of a ladder-like pattern seen within Phylum Platyhelminthes Have a radial arrangement of nerves instead of a ladder-like pattern seen within Phylum Platyhelminthes Phylum Acoelomorpha

14. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 14-14 Phylogeny of Acoelomorpha Phylogenetic studies describe acoelomorphs as early-diverging bilaterally, symmetrical triploblasts Phylogenetic studies describe acoelomorphs as early-diverging bilaterally, symmetrical triploblasts Have only four or five Hox genes Have only four or five Hox genes Phylum Acoelomorpha Phylum Acoelomorpha

15. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 14-15 Clades within Protostomia Divided into two large clades: Lophotrochozoa and Ecdysozoa Divided into two large clades: Lophotrochozoa and Ecdysozoa Before use of molecular phylogeny studies Before use of molecular phylogeny studies Protostomes grouped on the basis of body plan Protostomes grouped on the basis of body plan Molecular phylogenies Molecular phylogenies Group acoelomate and coelomate taxa together within the protostomes Group acoelomate and coelomate taxa together within the protostomes Ecdysozoa possess a cuticle that is molted as their bodies grow Ecdysozoa possess a cuticle that is molted as their bodies grow Phylum Acoelomorpha Phylum Acoelomorpha

16. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 14-16 Lophotrochozoa Lophotrochozoa Share either an odd horse-shoe shaped feeding structure, the lophophore Share either an odd horse-shoe shaped feeding structure, the lophophoreor Larval form called the trochophore Larval form called the trochophore Trochophore larvae Trochophore larvae Minute, translucent, and roughly top-shaped Minute, translucent, and roughly top-shaped Have a prominent circlet of cilia and sometimes one or two accessory circlets Have a prominent circlet of cilia and sometimes one or two accessory circlets Occur in the early development of marine members of Annelida and Mollusca Occur in the early development of marine members of Annelida and Mollusca Assumed to be the ancestors of such groups Assumed to be the ancestors of such groups Phylum Acoelomorpha Phylum Acoelomorpha

17. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 14-17 Phylum Platyhelminthes Characteristics Commonly called flatworms Commonly called flatworms Vary from a millimeter to many meters in length Vary from a millimeter to many meters in length Some free-living; others parasitic Some free-living; others parasitic Some argue that the phylum Platyhelminthes is not a valid monophyletic phylum Some argue that the phylum Platyhelminthes is not a valid monophyletic phylum The parasitic clades The parasitic clades Share an external body covering called a syncytial tegument or neodermis Share an external body covering called a syncytial tegument or neodermis

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19. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 14-19 Platyhelminthes is divided into four classes: Turbellaria, Trematoda, Monogenea, and Cestoda Platyhelminthes is divided into four classes: Turbellaria, Trematoda, Monogenea, and Cestoda Class Turbellaria Class Turbellaria Mostly free-living forms Mostly free-living forms Most are bottom dwellers in marine or freshwater Most are bottom dwellers in marine or freshwater Freshwater planarians Freshwater planarians Found in streams, pools, and hot springs Found in streams, pools, and hot springs Terrestrial flatworms limited to moist places Terrestrial flatworms limited to moist places All members of Monogenea and Trematoda (flukes) and Cestoda (tapeworms) are parasitic All members of Monogenea and Trematoda (flukes) and Cestoda (tapeworms) are parasitic Phylum Platyhelminthes

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21. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 14-21 Form and Function Epidermis and Muscles Epidermis and Muscles Most have cellular, ciliated epidermis on a basement membrane Most have cellular, ciliated epidermis on a basement membrane Rod-shaped rhabdites Rod-shaped rhabdites Swell and form a protective mucous sheath Swell and form a protective mucous sheath Most turbellarians have dual-gland adhesive organs Most turbellarians have dual-gland adhesive organs Viscid gland cells fasten microvilli of anchor cells to substrate Viscid gland cells fasten microvilli of anchor cells to substrate Secretions of releasing gland cells provide a quick chemical detachment Secretions of releasing gland cells provide a quick chemical detachment Phylum Platyhelminthes

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24. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 14-24 Some turbellarians, and all other members of this phylum Some turbellarians, and all other members of this phylum Have a syncytial epidermis Have a syncytial epidermis Nuclei are not separated by cell membranes Nuclei are not separated by cell membranes Non-turbellarians Non-turbellarians Lack cilia and have a tegument Lack cilia and have a tegument Form the subphylum Neodermata Form the subphylum Neodermata Under the basement membrane Under the basement membrane Muscle fibers run circularly, longitudinally and diagonally Muscle fibers run circularly, longitudinally and diagonally Parenchyma cells fill spaces in the body Parenchyma cells fill spaces in the body In some, if not all, these are noncontractile portions of muscle cells In some, if not all, these are noncontractile portions of muscle cells Phylum Platyhelminthes

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26. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 14-26 Nutrition and Digestion Cestodes have no digestive system Cestodes have no digestive system Others have a mouth, pharynx, and intestine Others have a mouth, pharynx, and intestine In planarians In planarians Pharynx may extend through the ventral mouth Pharynx may extend through the ventral mouth Intestine has three branches Intestine has three branches One anterior and two posterior One anterior and two posterior Gastrovascular cavity lined with columnar epithelium Gastrovascular cavity lined with columnar epithelium Mouth of trematodes and monogeneans Mouth of trematodes and monogeneans Opens near the anterior end Opens near the anterior end Pharynx is not extensible Pharynx is not extensible Intestine ends blindly, varies in degree of branching Intestine ends blindly, varies in degree of branching Phylum Platyhelminthes

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30. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 14-30 Planaria Planaria Carnivorous and detect food by chemoreceptors Carnivorous and detect food by chemoreceptors Food trapped in mucous secretions from glands and rhabdites Food trapped in mucous secretions from glands and rhabdites Wrap themselves around prey Wrap themselves around prey Extend the proboscis to suck up bits of food Extend the proboscis to suck up bits of food Phylum Platyhelminthes

31. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 14-31 Monogeneans and Trematodes Monogeneans and Trematodes Feed on host cells, cellular debris, and body fluids Feed on host cells, cellular debris, and body fluids Proteolytic enzymes from the intestine are secreted for extracellular digestion Proteolytic enzymes from the intestine are secreted for extracellular digestion Phagocytic cells in gastrodermis complete digestion at intracellular level Phagocytic cells in gastrodermis complete digestion at intracellular level Undigested food egested out the pharynx Undigested food egested out the pharynx Cestodes Cestodes Rely on the host’s digestive tract Rely on the host’s digestive tract Absorb digested nutrients Absorb digested nutrients Phylum Platyhelminthes

32. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 14-32 Excretion and Osmoregulation Flatworms have protonephridia Flatworms have protonephridia Used for osmoregulation Used for osmoregulation Beating flagella drive fluids down collecting ducts Beating flagella drive fluids down collecting ducts Wall of the duct beyond the flame cell bears folds or microvilli to resorb ions and molecules Wall of the duct beyond the flame cell bears folds or microvilli to resorb ions and molecules Majority of metabolic wastes Majority of metabolic wastes Removed by diffusion across the cell wall Removed by diffusion across the cell wall Collecting ducts join and empty at nephridiopores Collecting ducts join and empty at nephridiopores Marine turbellarians Marine turbellarians Lack these units Lack these units No need to expel excess water No need to expel excess water Phylum Platyhelminthes

33. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 14-33 Monogeneans have two excretory pores Monogeneans have two excretory pores Open laterally near anterior end Open laterally near anterior end Flame cell protonephridia present also parasitic taxa Flame cell protonephridia present also parasitic taxa Ducts of trematodes open into excretory bladder that opens to a terminal pore Ducts of trematodes open into excretory bladder that opens to a terminal pore Cestodes have two main excretory canals on each side Cestodes have two main excretory canals on each side Metabolic wastes are removed largely by diffusion through the body wall Metabolic wastes are removed largely by diffusion through the body wall Phylum Platyhelminthes

34. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 14-34 Nervous System Subepidermal nerve plexus resembles nerve net of cnidarians Subepidermal nerve plexus resembles nerve net of cnidarians One to five pairs of longitudinal nerve cords lie under the muscle layer One to five pairs of longitudinal nerve cords lie under the muscle layer More derived flatworms have fewer nerve cords More derived flatworms have fewer nerve cords Freshwater planarians Freshwater planarians One ventral pair of nerve cords forming a ladder- type pattern One ventral pair of nerve cords forming a ladder- type pattern Brain is a bilobed ganglion anterior to the ventral nerve cords Brain is a bilobed ganglion anterior to the ventral nerve cords Phylum Platyhelminthes

35. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 14-35 Sense Organs Active locomotion favored cephalization and evolution of sense organs Active locomotion favored cephalization and evolution of sense organs Ocelli (light-sensitive eyespots) Ocelli (light-sensitive eyespots) Present in turbellarians, monogeneans, and larval trematodes Present in turbellarians, monogeneans, and larval trematodes Tactile and chemoreceptive cells Tactile and chemoreceptive cells Abundant, especially in the ear-shaped auricles Abundant, especially in the ear-shaped auricles Statocysts (equilibrium) and rheoreceptors (sense direction of water currents) in some Statocysts (equilibrium) and rheoreceptors (sense direction of water currents) in some Sensory nerve endings found in Sensory nerve endings found in Oral suckers and genital pores of parasitic groups Oral suckers and genital pores of parasitic groups Phylum Platyhelminthes

36. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 14-36 Reproduction and Regeneration Fission Fission Many turbellarians constrict behind the pharynx and separate into two animals Many turbellarians constrict behind the pharynx and separate into two animals Each half regenerates the missing parts Each half regenerates the missing parts Provides for rapid population growth Provides for rapid population growth Some do not separate immediately, creating chains of zooids Some do not separate immediately, creating chains of zooids Regeneration Regeneration If the head and tail are cut off If the head and tail are cut off Each end grows the missing part; it retains polarity Each end grows the missing part; it retains polarity Extract of heads added to a culture of headless worms prevents regeneration Extract of heads added to a culture of headless worms prevents regeneration Phylum Platyhelminthes

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38. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 14-38 Some asexual reproduction occurs in intermediate hosts Some asexual reproduction occurs in intermediate hosts Nearly all are monoecious but cross-fertilize Nearly all are monoecious but cross-fertilize Endolecithal eggs with spiral determinate cleavage are typical and ancestral Endolecithal eggs with spiral determinate cleavage are typical and ancestral Some turbellarians and all other groups have female gametes with little yolk Some turbellarians and all other groups have female gametes with little yolk Yolk is contributed by separate organs, vitellaria Yolk is contributed by separate organs, vitellaria Vitelline ducts bring yolk cells to the zygote (ectolecithal development) Vitelline ducts bring yolk cells to the zygote (ectolecithal development) A cleavage pattern cannot be distinguished A cleavage pattern cannot be distinguished Zygote and yolk cells surrounded by eggshell move into the uterus Zygote and yolk cells surrounded by eggshell move into the uterus Phylum Platyhelminthes

39. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 14-39 Male Structures Male Structures One or more testes are connected to vasa efferentia that connect to one vas deferens One or more testes are connected to vasa efferentia that connect to one vas deferens The vas deferens runs to a seminal vesicle The vas deferens runs to a seminal vesicle A papilla-like penis or extensible cirrus is the copulatory organ A papilla-like penis or extensible cirrus is the copulatory organ Turbellarians develop male and female organs opening at a common pore Turbellarians develop male and female organs opening at a common pore After copulation, eggs and yolk cells enclosed in small cocoon After copulation, eggs and yolk cells enclosed in small cocoon Attach by a stalk to plants Attach by a stalk to plants Embryos emerge and resemble little adults Embryos emerge and resemble little adults Embryos of some marine forms are ciliated, free- swimming larvae Embryos of some marine forms are ciliated, free- swimming larvae Phylum Platyhelminthes

40. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 14-40 Larval trematodes emerge as ciliated larvae Larval trematodes emerge as ciliated larvae Penetrate a snail or eaten by a host Penetrate a snail or eaten by a host Cestodes hatch only after being consumed by a host Cestodes hatch only after being consumed by a host Many different animals can serve as intermediate hosts Many different animals can serve as intermediate hosts Trematoda, Monogenea, and Cestoda Trematoda, Monogenea, and Cestoda United into a single clade called Neodermata United into a single clade called Neodermata Phylum Platyhelminthes

41. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 14-41 Class Turbellaria Mostly free-living Mostly free-living Range from 5 mm to 50 cm long Range from 5 mm to 50 cm long Except for polyclads, endolecithal turbellarians Except for polyclads, endolecithal turbellarians Simple gut or no gut and a simple pharynx Simple gut or no gut and a simple pharynx Polyclads have a folded pharynx and a gut with many branches Polyclads have a folded pharynx and a gut with many branches Larger polyclads have more highly branched intestines Larger polyclads have more highly branched intestines Phylum Platyhelminthes

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43. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 14-43 Members of order Tricladidia are ectolecithal Members of order Tricladidia are ectolecithal Have a three-branched intestine Have a three-branched intestine Very small planaria swim by cilia Very small planaria swim by cilia Others move by cilia Others move by cilia Glide over a slime track secreted by adhesive glands Glide over a slime track secreted by adhesive glands Rhythmical muscular waves pass backward from the head Rhythmical muscular waves pass backward from the head Phylum Platyhelminthes

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45. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 14-45 Class Trematoda All trematodes are parasitic flukes All trematodes are parasitic flukes Most adults are endoparasites of vertebrates Most adults are endoparasites of vertebrates They resemble ectolecithal turbellaria but the tegument lacks cilia in adults They resemble ectolecithal turbellaria but the tegument lacks cilia in adults Adaptations for parasitism include: Adaptations for parasitism include: Penetration glands Penetration glands Glands to produce cyst material Glands to produce cyst material Hooks and suckers for adhesion Hooks and suckers for adhesion Increased reproductive capacity Increased reproductive capacity Phylum Platyhelminthes

46. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 14-46 Some trematodes retain ancestral characteristic of Some trematodes retain ancestral characteristic of Alimentary canal and reproductive, excretory and nervous systems Alimentary canal and reproductive, excretory and nervous systems Sense organs are poorly developed Sense organs are poorly developed Phylum Platyhelminthes

47. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 14-47 Subclass Aspidogastrea Least well-known Least well-known Most have only a single host Most have only a single host Usually a mollusk Usually a mollusk If there is a second host If there is a second host Usually a fish or turtle Usually a fish or turtle Phylum Platyhelminthes

48. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 14-48 Subclass Digenea Indirect life cycle in most Indirect life cycle in most First intermediate host a mollusc First intermediate host a mollusc Definitive or final host Definitive or final host Vertebrate Vertebrate Organisms reproduce sexually in this host Organisms reproduce sexually in this host A 2 nd or 3 rd intermediate host may be required in the life cycle A 2 nd or 3 rd intermediate host may be required in the life cycle Parasitize a wide range of hosts Parasitize a wide range of hosts Phylum Platyhelminthes

49. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 14-49 General Digenean Life Cycle General Digenean Life Cycle Egg passes from definitive host in excreta and must reach water Egg passes from definitive host in excreta and must reach water Hatches into a free-swimming ciliated larva, the miracidium Hatches into a free-swimming ciliated larva, the miracidium Miracidium penetrates tissues of a snail Miracidium penetrates tissues of a snail Transforms into a sporocyst Transforms into a sporocyst Sporocyst reproduces asexually to form sporocysts or rediae Sporocyst reproduces asexually to form sporocysts or rediae Rediae reproduce asexually and form rediae or cercariae Rediae reproduce asexually and form rediae or cercariae Phylum Platyhelminthes

50. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 14-50 Cercariae emerge from the snail Cercariae emerge from the snail Penetrate a 2 nd intermediate host or encyst on objects Penetrate a 2 nd intermediate host or encyst on objects Develop into metacercariae (juvenile flukes) Develop into metacercariae (juvenile flukes) Metacercaria develop into adults when eaten by definitive host when Metacercaria develop into adults when eaten by definitive host when Some serious parasites of humans and domestic animals are digeneans Some serious parasites of humans and domestic animals are digeneans Phylum Platyhelminthes

51. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 14-51 Sheep Liver Fluke Fasciola hepatica Fasciola hepatica First digenean whose life cycle was described First digenean whose life cycle was described Adult fluke lives in bile passageways in the liver of sheep and other ruminants Adult fluke lives in bile passageways in the liver of sheep and other ruminants Eggs are pass out in feces Eggs are pass out in feces Miracidia hatch and penetrate snails to become sporocysts Miracidia hatch and penetrate snails to become sporocysts After two generations of rediae After two generations of rediae Cercaria encyst on vegetation and await being eaten by sheep Cercaria encyst on vegetation and await being eaten by sheep When eaten, metacercariae develop into young flukes When eaten, metacercariae develop into young flukes Phylum Platyhelminthes

52. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 14-52 Clonorchis sinensis: Human Liver Fluke Most important human liver fluke Most important human liver fluke Common in China, Japan, and Southeast Asia Common in China, Japan, and Southeast Asia Also infects cats, dogs, and pigs Also infects cats, dogs, and pigs Adult fluke is 10–20 mm long with an oral and ventral sucker Adult fluke is 10–20 mm long with an oral and ventral sucker Digestive system includes pharynx, esophagus, and two long intestinal ceca Digestive system includes pharynx, esophagus, and two long intestinal ceca Excretory system has two protonephridial tubules with branches with flame cells Excretory system has two protonephridial tubules with branches with flame cells Phylum Platyhelminthes

53. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 14-53 Nervous system Nervous system Two cerebral ganglia and longitudinal cords with transverse connectives Two cerebral ganglia and longitudinal cords with transverse connectives Males Males Testes, two vasa efferentia uniting to a vas deferens, seminal vesicle, and ejaculatory duct Testes, two vasa efferentia uniting to a vas deferens, seminal vesicle, and ejaculatory duct No cirrus No cirrus Females Females Branched ovary, and a short oviduct joined by ducts from seminal receptacle and vitellaria at the ootype Branched ovary, and a short oviduct joined by ducts from seminal receptacle and vitellaria at the ootype Ootype is surrounded by Mehlis’ gland Ootype is surrounded by Mehlis’ gland Uterus then extends to the genital pore Uterus then extends to the genital pore Phylum Platyhelminthes

54. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 14-54 Clonorchis Life Cycle Adults live in bile passageways of humans and other fish-eating mammals Adults live in bile passageways of humans and other fish-eating mammals Eggs containing a complete miracidium are shed into water with feces Eggs containing a complete miracidium are shed into water with feces The eggs hatch only when ingested by snails of specific genera The eggs hatch only when ingested by snails of specific genera Miracidium enters snail tissue and transforms into a sporocyst Miracidium enters snail tissue and transforms into a sporocyst Sporocyst produces one generation of rediae, which begin differentiation Sporocyst produces one generation of rediae, which begin differentiation Phylum Platyhelminthes

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56. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 14-56 Rediae pass into the snail liver Rediae pass into the snail liver Continue embryonation into tadpole-like cercariae Continue embryonation into tadpole-like cercariae Cercariae escape into water Cercariae escape into water Make contact a fish in the family Cyprinidae Make contact a fish in the family Cyprinidae Bore into fish muscles or under scales Bore into fish muscles or under scales Shed tail and encyst as metacercariae Shed tail and encyst as metacercariae A mammal eats raw fish A mammal eats raw fish Cyst dissolves and flukes migrate up bile duct Cyst dissolves and flukes migrate up bile duct Heavy infection can destroy the liver and result in death Heavy infection can destroy the liver and result in death Control of parasites Control of parasites Destroy snails and thoroughly cook fish Destroy snails and thoroughly cook fish Phylum Platyhelminthes

57. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 14-57 Schistosoma: Blood Flukes Over 200 million people infested with schistosomiasis Over 200 million people infested with schistosomiasis Common in Africa, South America, West Indies, and the Middle and Far East Common in Africa, South America, West Indies, and the Middle and Far East Sexes are separate Sexes are separate 3 species account for most human schistosomiasis: 3 species account for most human schistosomiasis: S. mansoni in venules of large intestine S. mansoni in venules of large intestine S. japonicum in venules of small intestine S. japonicum in venules of small intestine S. haemotobium in venules of urinary bladder S. haemotobium in venules of urinary bladder Phylum Platyhelminthes

58. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 14-58 Schistosoma Life Cycle Eggs discharged in human feces or urine Eggs discharged in human feces or urine In water, eggs hatch as ciliated miracidia In water, eggs hatch as ciliated miracidia Must contact a particular species of snail to survive Must contact a particular species of snail to survive In the snail, they transform to sporocysts In the snail, they transform to sporocysts Sporocysts produce cercaria directly Sporocysts produce cercaria directly Cercariae escape the snail and swim until they contact bare human skin Cercariae escape the snail and swim until they contact bare human skin Cercariae pierce the skin and shed their tails Cercariae pierce the skin and shed their tails Phylum Platyhelminthes

59. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 14-59 Enter blood vessels and migrate to the hepatic portal blood vessels Enter blood vessels and migrate to the hepatic portal blood vessels Develop in the liver and they migrate target sites Develop in the liver and they migrate target sites Eggs released by females are extruded through gut or bladder lining and exit with feces or urine Eggs released by females are extruded through gut or bladder lining and exit with feces or urine Eggs that remain behind become centers of inflammation Eggs that remain behind become centers of inflammation Phylum Platyhelminthes

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62. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 14-62 Eggs of S. mansoni and S. japonicum Eggs of S. mansoni and S. japonicum Damage the intestinal wall Damage the intestinal wall Eggs of S. haematobium Eggs of S. haematobium Damages the bladder wall Damages the bladder wall Control: proper disposal of human wastes Control: proper disposal of human wastes Schistosome dermatitis (swimmer’s itch) Schistosome dermatitis (swimmer’s itch) Occurs when cercariae penetrate an unsuitable host such as a human Occurs when cercariae penetrate an unsuitable host such as a human Phylum Platyhelminthes

63. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 14-63 Paragonimus: Lung Flukes Paragonimus westermani Paragonimus westermani Lung fluke that parasitizes humans, pigs, rodents, etc. Lung fluke that parasitizes humans, pigs, rodents, etc. Eggs are coughed up in sputum, then swallowed and eliminated in feces Eggs are coughed up in sputum, then swallowed and eliminated in feces Zygotes develop in water and miricidia penetrate a snail host Zygotes develop in water and miricidia penetrate a snail host Within the snail, miricidia give rise to sporocysts, which develop into rediae Within the snail, miricidia give rise to sporocysts, which develop into rediae Phylum Platyhelminthes

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65. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 14-65 Cercariae are shed into the water and ingested by freshwater crabs Cercariae are shed into the water and ingested by freshwater crabs Metacercariae develop in freshwater crabs Metacercariae develop in freshwater crabs Human infection occurs by eating uncooked crabmeat Human infection occurs by eating uncooked crabmeat Phylum Platyhelminthes

66. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 14-66 Other Trematodes Fasciolopsis buski Fasciolopsis buski Lives in human intestines Lives in human intestines contracted from eating raw aquatic vegetation contracted from eating raw aquatic vegetation Leucochloridium Leucochloridium Produces remarkably colorful sporocysts in snails’ heads Produces remarkably colorful sporocysts in snails’ heads Attracts birds to eat snails and continue the life cycle Attracts birds to eat snails and continue the life cycle Phylum Platyhelminthes

67. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 14-67 Classification of Phylum Platyhelminthes Class Turbellaria Class Turbellaria Class Trematoda Class Trematoda Class Monogenea Class Monogenea Class Cestoda Class Cestoda Phylum Platyhelminthes

68. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 14-68 Class Monogenea Monogenetic flukes were originally placed in Trematoda Monogenetic flukes were originally placed in Trematoda Some now argue they are sister taxa, both having a posterior attachment with hooks Some now argue they are sister taxa, both having a posterior attachment with hooks External parasites of fish, especially gills, but a few are found in bladders of frogs and turtles External parasites of fish, especially gills, but a few are found in bladders of frogs and turtles Have direct life cycle in a single host Have direct life cycle in a single host Oncomiracidium attaches to host by posterior hooks Oncomiracidium attaches to host by posterior hooks Phylum Platyhelminthes

69. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 14-69 Posterior hooks may become the posterior attachment organ of the adult, the opisthaptor Posterior hooks may become the posterior attachment organ of the adult, the opisthaptor Opisthaptors vary widely (hooks, suckers, clamps) Opisthaptors vary widely (hooks, suckers, clamps) Withstand the force of water flow Withstand the force of water flow Some serious economic problems in fish farming Some serious economic problems in fish farming Phylum Platyhelminthes

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71. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 14-71 Class Cestoda Tapeworms have long flat bodies with scolex Tapeworms have long flat bodies with scolex Holdfast structure with suckers and hooks Holdfast structure with suckers and hooks Scolex is followed by a linear series of reproductive units or proglottids Scolex is followed by a linear series of reproductive units or proglottids Lack a digestive system Lack a digestive system Muscles, excretory and nervous systems similar to other flatworms Muscles, excretory and nervous systems similar to other flatworms Lack sensory organs except for modified cilia Lack sensory organs except for modified cilia Phylum Platyhelminthes

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73. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 14-73

74. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 14-74 Tegument is syncytial and has no cilia Tegument is syncytial and has no cilia Entire surface of cestodes is covered with projections (microtriches) similar to microvilli seen in the vertebrate small intestine Entire surface of cestodes is covered with projections (microtriches) similar to microvilli seen in the vertebrate small intestine Microtriches increase the surface area for food absorption Microtriches increase the surface area for food absorption Phylum Platyhelminthes

75. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 14-75 Subclass Eucestoda Aside from two orders of lesser importance, all have proglottids and are polyzoic Aside from two orders of lesser importance, all have proglottids and are polyzoic Larvae have six hooks on the scolex Larvae have six hooks on the scolex Chain of proglottids is called a strobila Chain of proglottids is called a strobila Proglottids originate in the germinative zone just behind the scolex Proglottids originate in the germinative zone just behind the scolex Some practice self-fertilization, although the norm is cross-fertilization Some practice self-fertilization, although the norm is cross-fertilization Shelled embryos form in the uterus Shelled embryos form in the uterus Either expelled or the whole proglottid is shed Either expelled or the whole proglottid is shed Phylum Platyhelminthes

76. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 14-76 Proglottid formation is not “true” segmentation Proglottid formation is not “true” segmentation Replication of sex organs not equivalent to metamerism in annelids, etc. Replication of sex organs not equivalent to metamerism in annelids, etc. Nearly all cestodes require two hosts Nearly all cestodes require two hosts Adult is parasitic in the digestive tract of the vertebrate Adult is parasitic in the digestive tract of the vertebrate Over 1000 species of tapeworms known, infecting almost all vertebrates Over 1000 species of tapeworms known, infecting almost all vertebrates Most tapeworms do little harm to host Most tapeworms do little harm to host Phylum Platyhelminthes

77. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 14-77 Taenia saginata: Beef Tapeworm Lives as an adult in the alimentary canal of humans Lives as an adult in the alimentary canal of humans Juvenile form found in intermuscular tissue of cattle Juvenile form found in intermuscular tissue of cattle Mature adults can reach over 10 meters in length with over 2000 proglottids Mature adults can reach over 10 meters in length with over 2000 proglottids Scolex has four suckers but no hooks Scolex has four suckers but no hooks Gravid proglottids (with shelled, infective larvae) pass in feces Gravid proglottids (with shelled, infective larvae) pass in feces Phylum Platyhelminthes

78. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 14-78 Excretory canals run from scolex along proglottids Excretory canals run from scolex along proglottids Flame cells attach to excretory ducts Flame cells attach to excretory ducts Nerve cords from a nerve ring in the scolex run along proglottids Nerve cords from a nerve ring in the scolex run along proglottids Each mature proglottid has muscles and parenchyma plus male and female organs Each mature proglottid has muscles and parenchyma plus male and female organs This order contains vitellaria in a single vitelline gland This order contains vitellaria in a single vitelline gland Gravid proglottids usually crawl out of feces Gravid proglottids usually crawl out of feces Proglottids rupture as they dry Proglottids rupture as they dry Embryos are viable for five months and are picked up by grazing Embryos are viable for five months and are picked up by grazing Phylum Platyhelminthes

79. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 14-79 Life Cycle Cattle swallow shelled larvae that hatch as oncospheres Cattle swallow shelled larvae that hatch as oncospheres Oncospheres use hooks to burrow through the intestinal wall into blood or lymph vessels Oncospheres use hooks to burrow through the intestinal wall into blood or lymph vessels When they reach voluntary muscle, they encyst to become bladder worms (cysticerci) When they reach voluntary muscle, they encyst to become bladder worms (cysticerci) When the infected meat is eaten, the cyst wall dissolves and the scolex evaginates to attach to intestinal mucosa When the infected meat is eaten, the cyst wall dissolves and the scolex evaginates to attach to intestinal mucosa Phylum Platyhelminthes

80. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 14-80 New proglottids develop in 2–3 weeks New proglottids develop in 2–3 weeks Infected individuals expel numerous proglottids daily Infected individuals expel numerous proglottids daily Infection can be avoided by eating only thoroughly cooked beef Infection can be avoided by eating only thoroughly cooked beef Phylum Platyhelminthes

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82. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 14-82

83. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 14-83 Taenia solium: Pork Tapeworm Adults live in small intestine of humans Adults live in small intestine of humans Juveniles live in muscles of pigs Juveniles live in muscles of pigs Scolex has both suckers and hooks on the rostellum Scolex has both suckers and hooks on the rostellum If eggs or proglottids are ingested If eggs or proglottids are ingested Embryos migrate to organs and form cysticerci Embryos migrate to organs and form cysticerci Cysticercosis commonly occurs in eyes or the brain blindness, serious neurological symptoms or death Cysticercosis commonly occurs in eyes or the brain blindness, serious neurological symptoms or death Infection can be avoided by eating thoroughly cooked pork Infection can be avoided by eating thoroughly cooked pork Phylum Platyhelminthes

84. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 14-84 Diphyllobothrium latum: Fish Tapeworm Adults found in intestines of humans, dogs, cats and other mammals Adults found in intestines of humans, dogs, cats and other mammals Immature stages found in crustaceans and fish Immature stages found in crustaceans and fish Largest cestode of humans, reaching up to 20 meters in length Largest cestode of humans, reaching up to 20 meters in length Phylum Platyhelminthes

85. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 14-85 Echinococcus granulosus: Unilocular Hydatid Adults parasitize dogs and other canines Adults parasitize dogs and other canines Juveniles infest many mammals Juveniles infest many mammals Humans may serve as intermediate host Humans may serve as intermediate host Juveniles are a special cysticercus, a hydatid cyst, that grows for up to 20 years Juveniles are a special cysticercus, a hydatid cyst, that grows for up to 20 years Main cyst maintains a single chamber Main cyst maintains a single chamber Daughter cysts bud off with thousands of scolices, each able to produce a worm if eaten Daughter cysts bud off with thousands of scolices, each able to produce a worm if eaten Surgical removal is the only treatment Surgical removal is the only treatment Phylum Platyhelminthes

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87. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 14-87 Phylogeny and Adaptive Diversification Of Platyhelminthes Phylogeny Phylogeny Even excluding acoels, the taxon Turbellaria is paraphyletic Even excluding acoels, the taxon Turbellaria is paraphyletic Ectolecithal turbellarians Ectolecithal turbellarians Allied with trematodes, monogeneans, and cestodes as the sister group to endolecithal turbellarians Allied with trematodes, monogeneans, and cestodes as the sister group to endolecithal turbellarians Neodermatans (trematodes, monogeneans, and cestodes) form a monophyletic group Neodermatans (trematodes, monogeneans, and cestodes) form a monophyletic group Phylum Platyhelminthes

88. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 14-88 Features of the most recent common ancestor is debated Features of the most recent common ancestor is debated Planuloid ancestor probably gave rise to sessile branch that was radial and another branch that became creeping and bilateral Planuloid ancestor probably gave rise to sessile branch that was radial and another branch that became creeping and bilateral Bilateral symmetry provided cephalization Bilateral symmetry provided cephalization Advantage where sensory structures move to the head Advantage where sensory structures move to the head Ancestral form would have had a simple body with a blind gut Ancestral form would have had a simple body with a blind gut Body shape and metabolic requirements ideal for parasitic lifestyles Body shape and metabolic requirements ideal for parasitic lifestyles Phylum Platyhelminthes

89. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 14-89 Phylum Mesozoa Considered a “missing link” between protozoa and metazoa Considered a “missing link” between protozoa and metazoa Have a simple level of organization Have a simple level of organization Minute, ciliated, and wormlike animals Minute, ciliated, and wormlike animals All live as parasites in marine invertebrates All live as parasites in marine invertebrates Most composed of only 20 to 30 cells arranged in two layers Most composed of only 20 to 30 cells arranged in two layers Layers are not homologous to germ layers of other metazoans Layers are not homologous to germ layers of other metazoans Two classes, Rhombozoa and Orthonectida, are so different that some authorities place them in separate phyla. Two classes, Rhombozoa and Orthonectida, are so different that some authorities place them in separate phyla.

90. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 14-90 Rhombozoans Live in kidneys of benthic cephalopods Live in kidneys of benthic cephalopods Adults called vermiforms and are long and slender Adults called vermiforms and are long and slender Inner, reproductive cells give rise to vermiform larvae Inner, reproductive cells give rise to vermiform larvae When overpopulated, reproductive cells develop into gonad-like structures producing male and female gametes When overpopulated, reproductive cells develop into gonad-like structures producing male and female gametes Larvae are shed with host urine into the seawater Larvae are shed with host urine into the seawater Phylum Mesozoa

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93. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 14-93 Orthonectids Parasitize variety of invertebrates Parasitize variety of invertebrates Reproduce sexually and asexually Reproduce sexually and asexually Asexual reproduction consists of a multinucleated mass called a plasmodium Asexual reproduction consists of a multinucleated mass called a plasmodium Phylum Mesozoa

94. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 14-94 Phylogeny of Mesozoans Some consider these organisms primitive flatworms and place them in phylum Platyhelminthes Some consider these organisms primitive flatworms and place them in phylum Platyhelminthes Molecular evidence groups them with flatworms in superphylum Lophotrochozoa Molecular evidence groups them with flatworms in superphylum Lophotrochozoa However, molecular phylogeny that included an orthonectid and two species from a rhombozoan subgroup, the dicyemids, did not show members of the two classes to be sister taxa However, molecular phylogeny that included an orthonectid and two species from a rhombozoan subgroup, the dicyemids, did not show members of the two classes to be sister taxa The phylum may not be monophyletic The phylum may not be monophyletic Phylum Mesozoa

95. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 14-95 Phylum Nemertea Characteristics Often called ribbon worms Often called ribbon worms Have a long muscular tube, the proboscis Have a long muscular tube, the proboscis Over 1000 species Over 1000 species Most are less than 20 cm long Most are less than 20 cm long General body plan similar to that of turbellarians General body plan similar to that of turbellarians Epidermis is ciliated with many gland cells Epidermis is ciliated with many gland cells Excretory system has flames cells; several have rhabdites Excretory system has flames cells; several have rhabdites Mostly dioecious Mostly dioecious

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99. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 14-99 Helmet-shaped pilidium larva Helmet-shaped pilidium larva Ventral mouth but no anus resembling flatworms and trochophore larvae of annelids and molluscs Ventral mouth but no anus resembling flatworms and trochophore larvae of annelids and molluscs Adult has an anus, producing a complete digestive system that is more efficient Adult has an anus, producing a complete digestive system that is more efficient Simplest animals with a blood-vascular system Simplest animals with a blood-vascular system Most are marine Most are marine Some are found in moist soil and freshwater Some are found in moist soil and freshwater Few are commensals or parasites Few are commensals or parasites Phylum Nemertea

100. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 14-100 Form and Function Slender and fragile Slender and fragile Amphiporus is a common example Amphiporus is a common example Dorsoventrally flattened with rounded ends Dorsoventrally flattened with rounded ends Body wall is ciliated columnar cells and layers of circular and longitudinal muscles Body wall is ciliated columnar cells and layers of circular and longitudinal muscles Partly gelatinous parenchyma fills space around organs Partly gelatinous parenchyma fills space around organs Anterior end has ocelli, a mouth and a separate opening of the proboscis Anterior end has ocelli, a mouth and a separate opening of the proboscis Phylum Nemertea

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102. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 14-102 Proboscis is an eversible organ Proboscis is an eversible organ Protruded from a rhynchocoel for defense and catching prey Protruded from a rhynchocoel for defense and catching prey Proboscis is everted by fluid pressure and retracted by muscles Proboscis is everted by fluid pressure and retracted by muscles Has a sharp-pointed stylet at the tip Has a sharp-pointed stylet at the tip Phylum Nemertea

103. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 14-103 Locomotion Movement is by both musculature and cilia Movement is by both musculature and cilia Some glide on the substrate Some glide on the substrate Some use the proboscis to attach and draw the body forward Some use the proboscis to attach and draw the body forward Phylum Nemertea

104. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 14-104 Feeding and Digestion Carnivorous: Feed on dead or living prey Carnivorous: Feed on dead or living prey Slime-covered proboscis wraps around prey Slime-covered proboscis wraps around prey Stylet pierces and holds prey until it is thrust into mouth Stylet pierces and holds prey until it is thrust into mouth Pours a neurotoxin, tetrodotoxin (the toxin in puffer fishes) on its prey Pours a neurotoxin, tetrodotoxin (the toxin in puffer fishes) on its prey Complete digestive system has a dilated stomach and an intestine with lateral ceca Complete digestive system has a dilated stomach and an intestine with lateral ceca The tract is lined with ciliated epithelium and glandular cells in the esophagus The tract is lined with ciliated epithelium and glandular cells in the esophagus Food digested in the intestinal tube is absorbed into the blood-vascular system Food digested in the intestinal tube is absorbed into the blood-vascular system Phylum Nemertea

105. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 14-105 Circulation Blood-vascular system Blood-vascular system Single dorsal vessel and two lateral vessels Single dorsal vessel and two lateral vessels Blood is colorless and contains nucleated corpuscles Blood is colorless and contains nucleated corpuscles Some have colored pigments with unknown functions Some have colored pigments with unknown functions No heart No heart Blood moved by muscular walls of blood vessels and by body movements Blood moved by muscular walls of blood vessels and by body movements Phylum Nemertea

106. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 14-106 Excretion and Respiration Near the edge of body is a lateral tube with branches and flame cells Near the edge of body is a lateral tube with branches and flame cells Wastes picked up from parenchymal spaces by flame cells are carried out excretory ducts Wastes picked up from parenchymal spaces by flame cells are carried out excretory ducts Protonephridia are so closely associated with circulatory system that they are truly excretory rather than simply osmoregulatory in function as in flatworms Protonephridia are so closely associated with circulatory system that they are truly excretory rather than simply osmoregulatory in function as in flatworms Respiration occurs through the body surface Respiration occurs through the body surface Phylum Nemertea

107. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 14-107 Nervous System Brain composed of Brain composed of Four fused ganglia, one pair dorsal and one pair ventral Four fused ganglia, one pair dorsal and one pair ventral Five longitudinal nerves extend backward from the brain Five longitudinal nerves extend backward from the brain The proboscis, ocelli and other sense organs have nerves leading to the brain The proboscis, ocelli and other sense organs have nerves leading to the brain Sense organs include tactile papillae, sensory pits and grooves, and probably auditory organs Sense organs include tactile papillae, sensory pits and grooves, and probably auditory organs Phylum Nemertea

108. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 14-108 Reproduction and Development Amphiporus is dioecious Amphiporus is dioecious Gonads discharge eggs or sperm through short ducts Gonads discharge eggs or sperm through short ducts Fertilization occurs in the water Fertilization occurs in the water As eggs are produced, other visceral organs degenerate As eggs are produced, other visceral organs degenerate Cleavage is spiral and determinate Cleavage is spiral and determinate Mesoderm derived from both endoderm and ectoderm Mesoderm derived from both endoderm and ectoderm Phylum Nemertea

109. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 14-109 Rhynchocoel develops from mesoderm but is not homologous to the coelom in other coelomate phyla Rhynchocoel develops from mesoderm but is not homologous to the coelom in other coelomate phyla Pilidium larvae bears a dorsal spike of fused cilia and lateral lobes Pilidium larvae bears a dorsal spike of fused cilia and lateral lobes Phylum Nemertea

110. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 14-110 Regeneration Nemerteans regenerate readily Nemerteans regenerate readily Some fragment themselves during certain seasons Some fragment themselves during certain seasons Tail sections can regenerate a new proboscis within a short time Tail sections can regenerate a new proboscis within a short time Phylum Nemertea

111. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 14-111 Classification of Phylum Nemertea Class Enopla Class Enopla Class Anopla Class Anopla Phylogeny of Nemertea Much debate about the phylogenetic position of nemerteans Much debate about the phylogenetic position of nemerteans Larval forms vary Larval forms vary Nemertean body plan is controversial Nemertean body plan is controversial Are they coelomate or acoelomate? Are they coelomate or acoelomate? Phylum Nemertea