Questions and Answers
What does the name 'Platyhelminthes' mean in Latin?
platy = flat, helminth = worm
What is the phylogenetic diagnosis of Phylum Platyhelminthes?
- First organisms to evolve bilateral symmetry, 2. Most are dorsoventrally flattened, 3. Acoelomate with packed parenchymal cells, 4. Small degree of cephalization, 5. Three germ cell layers, 6. Undergo determinate spiral cleavage, 7. Parenchymal cells make up the mesoglea.
Describe the evolutionary advances 'pioneered' by phylum Platyhelminthes.
- Cephalization, 2. Bilateral symmetry, 3. Tripoblasty
What is primary bilateral symmetry?
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What are the characteristics of Phylum Acoelomorpha?
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Describe the general features of phylum Platyhelminthes.
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List some representatives of each class in phylum Platyhelminthes.
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Which three classes of Platyhelminthes are parasitic? Which class is non-parasitic?
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How do the body forms of parasitic and non-parasitic flatworms differ?
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What are rhabdites?
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What are the two glands of the dual-gland adhesive organ of Tubellarians?
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Which class in phylum Platyhelminthes lacks a digestive system?
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Describe the sensory capabilities of Platyhelminthes.
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How do Tubellarians reproduce?
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What is the difference between ectolecithal and endolecithal development?
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Study Notes
Phylum Platyhelminthes Overview
- "Platyhelminthes" translates to "flat worms" with "platy" meaning flat and "helminth" meaning worm.
- Characterized by bilateral symmetry, acoelomate structure, and a flattened body shape.
- Possess a region filled with parenchymal cells between the gut and epidermis, providing structural support.
Evolutionary Advances
- Cephalization allows for enhanced sensory capabilities concentrated in the head region.
- Exhibits primary bilateral symmetry, facilitating directed movement and body organization.
- Triploblastic construction, possessing three germ layers: ectoderm, endoderm, and mesoderm.
- Undergo determinate spiral cleavage during embryonic development.
General Features
- Size ranges from a few millimeters to several meters, with both free-living and parasitic species.
- Parasitic species possess a protective layer called the neodermis to guard against host digestive enzymes.
- Gas and ion exchange occur through the body surface.
Class Representatives
- Class Trematoda: Includes sheep-liver fluke, Schistoma spp., Clonorchis sinensis.
- Class Cestoda: Notable for Taenia saginata (beef tapeworm).
- Class Monogenea: Includes Polystoma integerrimum, which parasitizes amphibians.
- Class Turbellaria: Encompasses Planaria spp., recognized as free-living flatworms.
Parasitic vs Non-Parasitic Differences
- Parasitic classes (Trematoda, Cestoda, Monogenea) generally lack cilia in adulthood and possess a neodermis.
- Non-parasitic Tubellarians feature a dual-gland adhesive system, cilia throughout life, and specialized features for osmoregulation in freshwater species.
- Parasitic flatworms have higher reproductive output due to reduced energy requirements for obtaining nutrients.
Rhabdites
- Rhabdites are rod-shaped cells found in the epidermis of Turbellarians, producing mucus that enhances locomotion and prevents desiccation.
Dual-gland Adhesive Organ
- Tubellarians have two types of glands: viscid glands for attachment to substrates and releasing glands for quick detachment.
Digestive System
- Class Cestoda is unique in lacking a digestive system, whereas other classes maintain a mouth, pharynx, and intestine.
Sensory Capabilities
- Tubellarians and Monogeneans have ocelli for light detection and tactile/chemoreceptive cells for sensory perception.
- Parasitic species detect prey via nerve endings on oral suckers and genital pores, enhancing electrical sensing.
Reproduction in Tubellarians
- Tubellarians reproduce asexually through transverse fission and sexually via ectolecithal development, involving yolk provision outside the embryo.
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This quiz features flashcards about Phylum Platyhelminthes, focusing on key terms and concepts related to flatworms. Learn the meaning of 'Platyhelminthes' and explore their phylogenetic significance and anatomical features. Ideal for biology students studying invertebrates.