Phylum Platyhelminthes & Cestodes Quiz
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Questions and Answers

What is the primary mode of lifestyle for organisms in the class Cestoda?

  • Commensal
  • Free living
  • Parasitic (correct)
  • Symbiotic

    • What structure do cestodes use to attach to the host's intestinal epithelium?

  • Scolex (correct)
  • Tegument
  • Proglottid
  • Strobila

    • Which of the following is true regarding the digestive system of cestodes?

  • It is absent (correct)
  • It has a simple structure
  • It is present and functional
  • It is similar to that of Monogenea

    • What unique characteristic do proglottids possess?

    <p>Each proglottid has both male and female reproductive systems</p> Signup and view all the answers

    Where is the germinative zone located in a cestode?

    <p>In the strobila</p> Signup and view all the answers

    How many eggs can individuals of large cestode species produce in a day?

    <p>1,000,000</p> Signup and view all the answers

    What is the role of microtriches in the tegument of cestodes?

    <p>Increase surface area for nutrient absorption</p> Signup and view all the answers

    How do proglottids exchange gametes?

    <p>Between proglottids of different worms or the same worm</p> Signup and view all the answers

    What happens after shelled oncospheres are ingested by cattle?

    <p>They hatch and lyse through the intestinal wall.</p> Signup and view all the answers

    What does the cyst of a cysticercus contain?

    <p>Scolex invaginated</p> Signup and view all the answers

    Which of the following is a key feature of trematodes' life cycle?

    <p>Life cycle typically includes 5 developmental stages.</p> Signup and view all the answers

    Where does the miracidium stage develop after penetrating the first intermediate host?

    <p>Into a sporocyst</p> Signup and view all the answers

    What type of replication occurs in the first intermediate host for trematodes?

    <p>Asexual replication</p> Signup and view all the answers

    What is a characteristic feature of the egg stage in trematodes' life cycle?

    <p>It usually contains miracidium.</p> Signup and view all the answers

    How does the scolex of a bladder worm attach to the intestine when ingested by the definitive host?

    <p>The cyst wall dissolves and the scolex evaginates.</p> Signup and view all the answers

    What is the primary function of the cercariae in the life cycle of trematodes?

    <p>To penetrate the skin of the second intermediate host</p> Signup and view all the answers

    What is the primary intermediate host for trematodes in their life cycle?

    <p>Snail</p> Signup and view all the answers

    At which stage do trematodes reproduce asexually to produce more cercariae?

    <p>Redia stage</p> Signup and view all the answers

    Which of the following accurately describes the role of metacercariae in trematode development?

    <p>They are eaten by the definitive host to complete the life cycle.</p> Signup and view all the answers

    In the life cycle of Clonorchis sinensis, which stage develops directly from the cercaria?

    <p>Metacercaria</p> Signup and view all the answers

    What does the term 'definitive host' refer to in the trematode life cycle?

    <p>The host where the parasite matures into an adult</p> Signup and view all the answers

    Which developmental stage immediately follows the sporocyst stage in trematodes?

    <p>Rediae</p> Signup and view all the answers

    Which statement correctly describes the secondary intermediate host in the trematode life cycle?

    <p>It is primarily a fish that is typically consumed by the definitive host.</p> Signup and view all the answers

    What is one of the key adaptations that cercariae possess for their role in the trematode life cycle?

    <p>Presence of a muscular tail for swimming</p> Signup and view all the answers

    What is the primary composition of the strobila in cestodes?

    <p>A chain of proglottids</p> Signup and view all the answers

    Which reproductive strategy most increases the potential gene exchange in cestodes?

    <p>Gamete exchange between different proglottids</p> Signup and view all the answers

    What characteristic of the tegument aids in nutrient absorption for cestodes?

    <p>Presence of microtriches</p> Signup and view all the answers

    Which class of Platyhelminthes includes organisms with an absent digestive system?

    <p>Cestoda</p> Signup and view all the answers

    What is a defining feature of each proglottid in cestodes?

    <p>Each has both male and female reproductive systems.</p> Signup and view all the answers

    In which zone are new proglottids produced in cestodes?

    <p>Germinative zone</p> Signup and view all the answers

    Which factor contributes to the immense reproductive capacity observed in large cestodes?

    <p>Individuals can produce a high number of eggs daily.</p> Signup and view all the answers

    What is the primary purpose of the scolex in cestodes?

    <p>To attach securely to the host</p> Signup and view all the answers

    What adaptation do cestodes lacking a digestive system exhibit?

    <p>Highly developed absorption structures</p> Signup and view all the answers

    What is the significance of the reproductive structure in proglottids for cestodes?

    <p>It ensures cross-fertilization between different worms.</p> Signup and view all the answers

    What is the life cycle stage of trematodes that develops after the miracidium stage and within the first intermediate host?

    <p>Sporocyst</p> Signup and view all the answers

    In trematodes, which host is associated with high species specificity for the first intermediate host?

    <p>First intermediate host</p> Signup and view all the answers

    What is the primary function of the cysticercus in the lifecycle of cestodes?

    <p>To act as a dormant stage until ingested.</p> Signup and view all the answers

    Which statement accurately describes a characteristic of the trematodes' asexual reproduction?

    <p>It typically occurs in the first intermediate host.</p> Signup and view all the answers

    What occurs during the cyst wall's dissolution when ingested by the definitive host?

    <p>The scolex evaginates and attaches to the intestine.</p> Signup and view all the answers

    In the context of trematodes, which of the following stages occurs immediately after the sporocyst stage?

    <p>Rediae</p> Signup and view all the answers

    In which organ systems can trematodes infest their definitive hosts?

    <p>Any organ system including liver and reproductive tracts</p> Signup and view all the answers

    What is the primary role of the cercariae in the life cycle of trematodes?

    <p>To penetrate a second intermediate host</p> Signup and view all the answers

    What is a characteristic feature of eggs in the trematode lifecycle?

    <p>They contain a free-swimming miracidium.</p> Signup and view all the answers

    Which developmental stage of trematodes is responsible for asexual reproduction leading to an increased number of cercariae?

    <p>Sporocyst</p> Signup and view all the answers

    Which aspect of the trematode life cycle is typically marked by asexual replication?

    <p>In the first intermediate host</p> Signup and view all the answers

    In the trematode life cycle, what happens to cercariae after they emerge from the snail host?

    <p>They penetrate the epidermis of a second intermediate host</p> Signup and view all the answers

    Which structure allows the cercariae to attach and infect the second intermediate host?

    <p>Oral sucker</p> Signup and view all the answers

    What transformation occurs to cercariae once they penetrate into the second intermediate host?

    <p>They transform into metacercariae</p> Signup and view all the answers

    Which stage serves as the infectious form for the definitive host in the trematode life cycle?

    <p>Metacercariae</p> Signup and view all the answers

    What is the first intermediate host typically for trematodes?

    <p>Snail</p> Signup and view all the answers

    What is the role of metacercariae in the trematode life cycle?

    <p>To serve as the larval stage that infects the definitive host</p> Signup and view all the answers

    Which characteristic feature distinguishes the cercariae stage in terms of morphology?

    <p>Oral sucker and muscular tail</p> Signup and view all the answers

    What is the life cycle stage that emerges from the egg containing a miracidium?

    <p>Cercaria</p> Signup and view all the answers

    What is the primary reproductive strategy observed in cestodes that enhances gene exchange?

    <p>Gamete exchange between proglottids</p> Signup and view all the answers

    Which of the following accurately describes the structure of the strobila in cestodes?

    <p>The strobila is a chain-like structure composed of multiple proglottids.</p> Signup and view all the answers

    What role do microtriches play in the tegument of cestodes?

    <p>They are involved in the absorption of nutrients.</p> Signup and view all the answers

    In cestodes, what is the significance of the germinative zone?

    <p>It is where new proglottids are produced.</p> Signup and view all the answers

    What anatomical feature distinguishes the scolex of a cestode?

    <p>Presence of hooks or suckers for attachment</p> Signup and view all the answers

    Which statement correctly describes the reproductive systems within a single proglottid of a cestode?

    <p>Each proglottid contains both male and female reproductive systems.</p> Signup and view all the answers

    Which characteristic of cestodes aids in their survival in the host's digestive system?

    <p>A tough tegument with microtriches</p> Signup and view all the answers

    What does the immense reproductive capacity of large cestodes imply about their ecological success?

    <p>They can rapidly colonize host populations.</p> Signup and view all the answers

    What happens to gonadal material in a proglottid as it matures?

    <p>It matures as the proglottid moves posteriorly along the strobila.</p> Signup and view all the answers

    What is the primary purpose of the metacercariae stage in the trematode life cycle?

    <p>To serve as an infectious form for the definitive host</p> Signup and view all the answers

    During which stage do trematodes undergo asexual reproduction to increase progeny?

    <p>Rediae</p> Signup and view all the answers

    In the life cycle of Clonorchis sinensis, which host experiences the cercariae penetration?

    <p>Second intermediate host (e.g., fish)</p> Signup and view all the answers

    What developmental feature do cercariae possess to aid in their host penetration?

    <p>Muscular tail</p> Signup and view all the answers

    What occurs after the miracidium stage in the trematode life cycle?

    <p>Rediae develop from the sporocyst</p> Signup and view all the answers

    Which feature distinguishes the developmental stages of trematodes?

    <p>Presence of oral and ventral suckers</p> Signup and view all the answers

    Which of the following accurately describes a characteristic of the rediae stage?

    <p>They contain developing cercariae</p> Signup and view all the answers

    How do cercariae achieve infection to the second intermediate host?

    <p>By penetrating the skin of the host</p> Signup and view all the answers

    What developmental stage immediately follows cercariae in the trematode lifecycle?

    <p>Metacercariae</p> Signup and view all the answers

    In which stage do trematodes primarily infect their definitive host?

    <p>Metacercariae</p> Signup and view all the answers

    What is the primary role of the cysticercus in the life cycle of cestodes?

    <p>To attach to the intestinal wall of the definitive host</p> Signup and view all the answers

    In the life cycle of trematodes, what is the significance of the sporocyst stage?

    <p>It undergoes asexual reproduction to produce additional stages</p> Signup and view all the answers

    How is the miracidium stage crucial to the lifecycle of trematodes?

    <p>It penetrates the first intermediate host's epidermis</p> Signup and view all the answers

    What defines the adult stage in trematodes?

    <p>It must inhabit a definitive vertebrate host for maturation</p> Signup and view all the answers

    What typically follows the release of eggs containing miracidia into the environment?

    <p>Miracidia develop into sporocysts in the first intermediate host</p> Signup and view all the answers

    What is the definition of a definitive host in the context of trematodes?

    <p>A host that harbors the adult stage of the organism</p> Signup and view all the answers

    Which characteristic of the first intermediate host is crucial for the life cycle of trematodes?

    <p>It ensures a high species specificity for the larval stages</p> Signup and view all the answers

    In the life cycle of cestodes, what occurs once the cyst wall is dissolved?

    <p>The scolex evaginates and attaches to the intestine</p> Signup and view all the answers

    What key feature distinguishes the eggs of trematodes in their lifecycle?

    <p>Contain a miracidium in a dormant state</p> Signup and view all the answers

    What is the main consequence of asexual replication in the first intermediate host of trematodes?

    <p>It results in an increased number of larval stages available for hosts</p> Signup and view all the answers

    Which characteristic distinguishes the class Turbellaria from other classes in Phylum Platyhelminthes?

    <p>Free-living lifestyle</p> Signup and view all the answers

    What does the term 'triploblastic acoelomate' imply about organisms in Phylum Platyhelminthes?

    <p>They have three tissue layers but lack a body cavity</p> Signup and view all the answers

    Which statement is accurate regarding the parasitic strategies of Cestoda?

    <p>They are exclusively internal parasites</p> Signup and view all the answers

    What type of symmetry is characteristic of organisms within the Phylum Platyhelminthes?

    <p>Bilateral symmetry</p> Signup and view all the answers

    Which of the following adaptations is typically NOT found in parasitic Platyhelminthes?

    <p>Complex nervous systems with advanced sensory structures</p> Signup and view all the answers

    In which aspect do the classes Trematoda and Monogenea primarily differ?

    <p>Type of intermediate host involved in their life cycles</p> Signup and view all the answers

    What is the primary role of the myofibrils in Platyhelminthes?

    <p>Enabling locomotion through muscle contractions</p> Signup and view all the answers

    Which of the following accurately describes the digestive tract in class Cestoda?

    <p>It is completely absent</p> Signup and view all the answers

    What unique characteristic do flukes (Trematoda) possess that distinguishes them from other Platyhelminthes?

    <p>The presence of multiple suckers for attachment</p> Signup and view all the answers

    Which class in Phylum Platyhelminthes primarily comprises organisms that are free-living?

    <p>Turbellaria</p> Signup and view all the answers

    What type of cell is the flame cell characterized by?

    <p>Inverted flagellated cell</p> Signup and view all the answers

    What structure is formed by the cellular interdigitation between the flame cell and the terminal tubule cell?

    <p>Mesh cup</p> Signup and view all the answers

    What is the primary purpose of the flagellar beat produced by the flame cell?

    <p>To create negative pressure</p> Signup and view all the answers

    In the protonephridium system, what process occurs to the fluid after it is drawn through the mesh?

    <p>It undergoes ultrafiltration</p> Signup and view all the answers

    What role do nephridopores play in the protonephridial system?

    <p>They serve as excretory pores</p> Signup and view all the answers

    Which feature of the tubule end cell supports its function in osmoregulation?

    <p>Its location at the end of the excretory system</p> Signup and view all the answers

    How does the modification of fluid occur in the tubule system?

    <p>By active transport of selective molecules</p> Signup and view all the answers

    What determines the efficiency of fluid draw into the flame cell?

    <p>The beating frequency of the flagella</p> Signup and view all the answers

    What does the term 'protonephridium' imply about its functionality?

    <p>It is the earliest form of excretory system</p> Signup and view all the answers

    What is the primary role of the mesh (weir) in the protonephridial system?

    <p>To aid in fluid entry from the flame cell</p> Signup and view all the answers

    Which nerve structure is characterized as being the simplest system, resembling a diffuse nerve net?

    <p>Subepidermal nerve plexus</p> Signup and view all the answers

    What arrangement forms when nerve cords connect with nerves creating a 'ladder-type' pattern?

    <p>Nerve cords with connecting nerves</p> Signup and view all the answers

    In addition to nerve cords, what feature contributes to a primitive nervous system?

    <p>Cerebral ganglion</p> Signup and view all the answers

    What role do rhabdites play in the structure of the epidermis?

    <p>They form a mucous coat for protection and locomotion.</p> Signup and view all the answers

    Which type of muscle is NOT found in the structure of planarians?

    <p>Radial muscle</p> Signup and view all the answers

    Which group of receptors is least likely to be associated with detecting gravity?

    <p>Ocelli</p> Signup and view all the answers

    What type of nerve structure lies beneath the musculature and consists of several pairs?

    <p>Longitudinal nerve cords</p> Signup and view all the answers

    What is the primary function of the dual-gland adhesive organs?

    <p>To attach and release the epidermis from the substrate.</p> Signup and view all the answers

    Which structure aids in the movement of planarians along a surface?

    <p>Ciliated ventral surface</p> Signup and view all the answers

    Which of these sensory receptors is primarily responsible for detecting chemical stimuli?

    <p>Chemoreceptors</p> Signup and view all the answers

    What is the function of auricles in relation to other structures in the nervous system?

    <p>Detect tactile signals</p> Signup and view all the answers

    What is NOT a component of the ciliated epidermis in planarians?

    <p>Longitudinal muscle</p> Signup and view all the answers

    Which type of receptors would be primarily responsible for detecting water currents?

    <p>Rheoreceptors</p> Signup and view all the answers

    What type of cell inserts rhabdites into the epidermis?

    <p>Parenchymal cell</p> Signup and view all the answers

    Which element is crucial for the locomotion of planarians?

    <p>Contraction of longitudinal and circular muscles</p> Signup and view all the answers

    The connection between nerve cords that resembles rungs on a ladder is formed by what?

    <p>Ring commissures</p> Signup and view all the answers

    What type of cells produce adhesive secretions for locomotion in planarians?

    <p>Anchor cells</p> Signup and view all the answers

    Which system is described as having a configuration that resembles a ringlike primitive nerve net?

    <p>Subepidermal nerve plexus</p> Signup and view all the answers

    Which of the following statements about the planarian nerve cord is true?

    <p>It mediates sensory information and body coordination.</p> Signup and view all the answers

    What facilitates the anchoring process during locomotion in planarians?

    <p>Viscid cell secretions</p> Signup and view all the answers

    Study Notes

    Phylum Platyhelminthes

    • Includes four classes: Turbellaria, Trematoda, Monogenea, and Cestoda.
    • Lifestyle varies: Turbellaria are free-living, while Trematoda, Monogenea, and Cestoda are parasitic.
    • Parasitic modes differ: internal (Trematoda, Cestoda), external (Monogenea).
    • Digestive tract presence varies: present in Turbellaria, Trematoda, and Monogenea; absent in Cestoda.

    Cestodes (Tapeworms)

    • Body (strobila) is a chain of proglottids.
    • Scolex is a specialized attachment structure to the host's intestinal epithelium.
    • Each proglottid contains male and female reproductive systems.
    • No digestive system; epidermis (tegument) has microtriches for nutrient absorption.
    • Germinative zone produces new proglottids; gonadal material matures posteriorly.
    • Gamete exchange occurs between proglottids of different or same worms.
    • Immense reproductive capacity; large species produce up to 1,000,000 eggs/day.

    Taenia saginata (Beef Tapeworm) Lifecycle

    • Gravid proglottids shed in feces; shelled larvae (oncospheres) develop.
    • Shelled oncospheres ingested by cattle.
    • Larvae hatch, lyse through intestinal wall, and form cysts (cysticercus) in muscle.
    • Cyst contains an invaginated scolex.
    • When ingested by definitive host, cyst dissolves; scolex evaginates and attaches to intestine.
    • Worm matures in 2-3 weeks.

    Trematodes (Flukes)

    • Life cycle typically includes five developmental stages and two or more intermediate hosts.
    • High species specificity for the first intermediate host (usually a snail), low specificity for others.
    • Adulthood only in a definitive vertebrate host.
    • Asexual replication of developmental stages, usually in the first intermediate host.
    • Adults live in definitive hosts; infestations can occur in various organ systems.
    • Eggs containing miracidia (first stage) are released in feces and require water.
    • Miracidium is a free-living, ciliated larva penetrating the first intermediate host.

    Trematode Developmental Stages

    • Miracidium develops into a sporocyst within the intermediate host.
    • Sporocysts reproduce asexually to yield more sporocysts or rediae.
    • Rediae (sac-like structures) contain developing cercariae and reproduce asexually, increasing progeny.
    • Free-swimming cercariae emerge, penetrate a second intermediate host (e.g., fish), and encyst as metacercariae.
    • Metacercariae are ingested by the definitive host.

    Clonorchis sinensis (Chinese Liver Fluke) Lifecycle

    • Metacercariae are ingested by the definitive host.
    • Adult flukes produce eggs containing miracidia.
    • Miracidia hatch in water and penetrate snails.
    • Sporocysts and rediae develop within the snail.
    • Cercariae emerge from the snail.

    Platyhelminthes Phylum

    • Includes classes Turbellaria (free-living), Trematoda (parasitic), Monogenea (parasitic), and Cestoda (parasitic).
    • Parasitic Platyhelminthes may be internal or external parasites.
    • Digestive tracts are present in Turbellaria, Trematoda, and Monogenea, but absent in Cestoda.

    Cestode Parasitic Strategies

    • Strobila: The body of the worm, composed of a chain of proglottids.
    • Scolex: Specialized structure for attachment to the host's intestinal epithelium.
    • Proglottid: Reproductive "section" containing both male and female reproductive systems.
    • Digestive System: Absent; the tegument (epidermis) has microtriches increasing surface area for nutrient absorption.
    • Germinative Zone: Produces new proglottids; gonadal material matures as proglottids move posteriorly.
    • Gamete Exchange: Occurs between proglottids of different or the same worm.
    • Reproductive Capacity: Immense; large species can produce up to 1,000,000 eggs/day.

    Taenia saginata (Beef Tapeworm) Lifecycle

    • Gravid proglottids shed in feces, releasing shelled larvae (oncospheres).
    • Cattle ingest shelled oncospheres.
    • Oncospheres hatch, lysing through the intestinal wall.
    • Larvae (cysticerci, bladder worms with an invaginated scolex) encyst in muscle tissue.
    • When ingested by the definitive host, the cyst wall dissolves; the scolex evaginates and attaches to the intestine.
    • The worm matures in 2-3 weeks.

    Trematode Parasitic Strategies

    • Life Cycle: Typically includes five developmental stages and two or more intermediate hosts.
    • Host Specificity: High for the first intermediate host (usually a snail), low for others and definitive hosts.
    • Adulthood: Only achieved in a definitive vertebrate host.
    • Asexual Replication: Occurs in developmental stages, normally in the first intermediate host.
    • Adult Trematodes: Live in definitive hosts (all vertebrate groups) and may infest various organ systems.
    • Egg: Contains a miracidium (first developmental stage) usually released in feces.
    • Miracidium: Free-living, ciliated larval stage penetrating the first intermediate host's epidermis.
    • Sporocyst (2nd stage): Develops from the miracidium and reproduces asexually, producing more sporocysts or rediae.
    • Rediae (3rd stage): Sac-like structures containing developing cercariae; reproduce asexually.
    • Cercariae (4th stage): Free-swimming, emerging from the snail host, penetrating a second intermediate host, or waiting to be eaten.
    • Metacercariae (5th stage): Encyst in the second intermediate host (e.g., fish).
    • Definitive Host: A vertebrate animal ingests the metacercariae.

    Clonorchis sinensis (Chinese Liver Fluke) Lifecycle

    • Metacercariae are ingested by the definitive host.
    • Adult flukes produce eggs containing miracidia.
    • Miracidia hatch in water and penetrate snails (first intermediate host).
    • Sporocysts and rediae develop asexually within the snail.
    • Cercariae are released from the snail.

    Platyhelminthes Phylum

    • Includes classes Turbellaria (free-living), Trematoda (parasitic), Monogenea (parasitic), and Cestoda (parasitic).
    • Parasitic Platyhelminthes can be internal or external parasites.
    • Digestive tracts are present in Turbellaria, Trematoda, and Monogenea, but absent in Cestoda.

    Cestodes (Tapeworms)

    • Body is a strobila: a chain of proglottids.
    • Scolex: specialized attachment structure to the host's intestinal epithelium.
    • Proglottid: reproductive section containing both male and female reproductive systems.
    • No digestive system; epidermis (tegument) has microtriches for nutrient absorption.
    • Germinative zone produces new proglottids; gonadal material matures as proglottids move posteriorly.
    • Gamete exchange occurs between proglottids of different or the same worm.
    • Immense reproductive capacity; large species can produce up to 1,000,000 eggs/day.

    Taenia saginata (Beef Tapeworm) Lifecycle

    • Gravid proglottids shed in feces; shelled larvae (oncospheres) develop.
    • Shelled oncospheres ingested by cattle.
    • Larvae hatch, lyse through intestinal wall, and form cysts (cysticercus) in muscle.
    • Cyst wall dissolves upon ingestion by definitive host; scolex evaginates and attaches to intestine.
    • Worm matures in 2-3 weeks.

    Trematodes (Flukes)

    • Typically have 5 developmental stages.
    • Typically involve 2 or more intermediate hosts.
    • High species specificity for the first intermediate host (usually a snail).
    • Low specificity for other intermediate and definitive hosts.
    • Adulthood only in a definitive vertebrate host.
    • Asexual replication of developmental stages, usually in the first intermediate host.

    Trematode Lifecycle Stages

    • Adult: Lives in the definitive host; infestation can occur in various organ systems.
    • Egg: Contains a miracidium (first developmental stage); released in feces and needs water.
    • Miracidium: Free-living, ciliated larva; penetrates the first intermediate host (usually a snail).
    • Sporocyst (second stage): Develops from the miracidium; reproduces asexually to yield more sporocysts or rediae.
    • Rediae (third stage): Sac-like structure containing developing cercariae; reproduces asexually to produce more cercariae.
    • Cercariae (fourth stage): Free-swimming; emerge from the snail and penetrate a second intermediate host or wait to be eaten.
    • Metacercariae (fifth stage): Encyst in the second intermediate host; ingested by the definitive host.

    Clonorchis sinensis (Chinese Liver Fluke) Lifecycle

    • Similar to the general trematode lifecycle, with metacercariae, adult fluke, eggs (containing miracidia), cercariae, rediae, and sporocysts. The lifecycle shows the progression through these stages.

    Phylum Platyhelminthes: Introduction

    • Flatworms, flukes, and tapeworms.
    • Includes classes Turbellaria (free-living), Trematoda (parasitic), Monogenea (parasitic), and Cestoda (parasitic).
    • Exhibit bilateral symmetry, are triploblastic acoelomates, and possess tissue-organ level organization.
    • Evolutionary relationships shown in a phylogenetic tree, placing them close to Nemerteans, Gastrotricha and Rotifers in a clade separate from other phyla shown.

    Body Form and Structures

    • Planarian cross-section shows dorsal (non-ciliated) and ventral (ciliated) epidermis.
    • Ventral epidermis facilitates locomotion via cilia.
    • Muscular layers (circular, longitudinal, parenchymal) present beneath epidermis.
    • Specialized epidermal structures:
      • Rhabdites: rod-shaped structures secreted from rhabdite cells; potentially involved in mucous coat formation.
      • Dual-gland adhesive organs: mediate attachment and release from substrates, aiding in locomotion. These organs involve viscid cells producing adhesive, anchor cells bearing the strain of attachment, and releasing cells secreting detachment chemicals.

    Locomotion

    • Achieved through a combination of: ciliated ventral surface, subtle muscular contractions, and dual-gland adhesive organs.

    Osmoregulation

    • Employ protonephridia (flame-bulb systems) for osmoregulation.
    • Flame cells possess flagella that create negative pressure, drawing fluid into tubules.
    • Fluid is ultrafiltered and further modified in the tubule system.
    • Modified fluid exits through excretory pores (nephridopores).

    Nervous Tissue

    • Three types of organization:

      • Subepidermal nerve plexus: simplest, resembling cnidarian nerve nets.
      • Subepidermal nerve plexus plus longitudinal nerve cords (1-5 pairs).
      • Nerve cords (1-3 pairs), connected by ring commissures (forming a "ladder-type" pattern), and a primitive brain (cerebral ganglion).

    • Sensory structures include auricles (containing tactile, chemoreceptors, rheoreceptors, statocysts, and photoreceptors (ocelli)).

    Neuromuscular System

    • Lateral nerve net contraction enables peristaltic movements.
    • Longitudinal myofibril contraction allows body and/or tentacle shortening.

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    Test your knowledge on Phylum Platyhelminthes and the lifecycle of Taenia saginata. This quiz covers classifications, lifestyles, and the unique features of tapeworms. Enhance your understanding of their anatomy, reproductive capacities, and parasitic adaptations.

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