Phylum Platyhelminthes: Flatworm Overview

Phylum Platyhelminthes Overview

• Comprised of flatworms, known for their flattened body shape.

Characteristics of Platyhelminthes

• Triploblastic: three germ layers (ectoderm, mesoderm, endoderm).
• Acoelomate: lack a body cavity.
• Exhibits spiral cleavage during embryonic development.
• Contains a sac-like gut for digestion.
• Cephalization present, with a distinct head region.
• Displays bilateral symmetry, flattened dorsoventrally.
• Protonephridia function as a primitive excretory system.
• Includes both parasitic and free-living species.
• Primarily hermaphroditic, possessing both male and female reproductive structures.

Structural Features

• Cerebral ganglion serves as a simple neural aggregation, functioning like a brain.
• Protonephridia function in excretion, resembling a basic kidney system.
• Body wall consists of epidermis, basement membrane, mesoderm, gland cells, and rhabdoids, providing structure and function.
• Bodies are covered with cilia aiding in locomotion and feeding.
• Nervous system designed like a ladder, also includes nerve cords and ganglia.

Mesoderm and Endoderm

• Mesoderm in Platyhelminths includes circular, diagonal, longitudinal, and dorsoventral muscle fibers aiding movement.
• Endodermal structure features a single cell layer, phagocytic cells, enzymatic glands, and can exhibit extracellular digestion.

Nephridiopores

• Structures that excrete waste water, functioning similarly to urine in higher organisms.

Sensory Organs

• Retinular cells detect light intensity, though they do not form images.
• Rheoreceptors sense mechanical stimuli in the environment.
• Chemoreceptors detect chemical signals, aiding in food detection and predator avoidance.

Classifications within Phylum Platyhelminthes

• Class Turbellaria:

  • Primarily free-living aquatic organisms with a ciliated epidermis.
  • Includes taxa such as Order Acoela (no permanent digestive cavity) and Order Polycladida (branched gut).

• Class Monogenea:

  • Ectoparasitic organisms with a life cycle in one host, featuring specialized attachment structures.

• Class Trematoda:

  • Endoparasitic species with complex life cycles involving multiple hosts.
  • Notable examples include Paragonimus westermani (Japanese lung fluke) and Schistosoma mansoni, which causes schistosomiasis.

• Class Cestoda:

  • Known for flat, ribbon-like form and absence of a digestive system, with the anterior scolex for attachment.
  • Includes Taenia saginata (beef tapeworm), transmitted through proglottids in feces.

Health Implications

• Schistosomiasis causes severe outcomes such as diarrhea, abdominal pain, liver damage, and impaired growth due to infection from schistosome species.
• Hosts for schistosomes include snails with a skin-penetrating free-living stage.

Reproduction

• Hermaphroditic condition allows for both male and female gamete production, enhancing reproductive success in various environments.

This quiz provides flashcards covering essential aspects of the Phylum Platyhelminthes, commonly known as flatworms. Explore their characteristics, structure, and classification. Ideal for students studying invertebrate zoology or related fields.