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Phylum Mollusca, Characteristics and Classification.pptx
- 1. Dr. Muhammad Moosa Abro Phylum Mollusca 1 Evolutionary Perspective Relationships to Other Animals Molluscan Characteristics Class Gastropoda Torsion Shell Coiling Locomotion Feeding and Digestion Other Maintenance Functions Reproduction and Development Gastropod Diversity Class Bivalvia Shell and Associated Structures Gas Exchange, Filter Feeding, and Digestion Other Maintenance Functions Reproduction and Development Bivalve Diversity Class Cephalopoda Shell Locomotion Feeding and Digestion Other Maintenance Functions Learning Reproduction and Development Class Polyplacophora Class Scaphopoda Class Monoplacophora Class Solenogastres Class Caudofoveata Further Phylogenetic Considerations
- 3. 3 EVOLUTIONARY PERSPECTIVE Dr. Muhammad Moosa Abro Phylum Mollusca Octopuses, squids, and cuttlefish (Cephalopods) are some of the invertebrate world’s most adept predators. Predatory lifestyles have resulted in the evolution of large, complex sensory structures, rapid locomotion, grasping tentacles, and tearing mouthparts. Once numbering about 9,000 species, the class Cephalopoda now includes only about 550 species group has been very successful. If success is measured by numbers of species, the molluscs are twice as successful as vertebrates!
- 4. The vast majority of the nearly 100,000 living species of molluscs belongs to two classes: Gastropoda, the snails and slugs; and Bivalvia, the clams and their close relatives. Molluscs are triploblastic, Possess a coelom, although the coelom of molluscs is only a small cavity (the pericardial cavity) surrounding the heart, nephridia, and gonads. A coelom is a body cavity that arises in mesoderm and is lined by a sheet of mesoderm called the peritoneum 4 EVOLUTIONARY PERSPECTIVE Dr. Muhammad Moosa Abro Phylum Mollusca
- 5. Relationships to Other Animals 5 Molluscs are members of the Lophotrochozoa. Their lophotrochozoan relatives include the annelids, along with other phyla Dr. Muhammad Moosa Abro Phylum Mollusca
- 6. MOLLUSCAN CHARACTERISTICS Molluscs range in size and body form from the largest of all invertebrates, the giant squid (Architeuthis), measuring 18 m in length, to the smallest garden slug, less than 1 cm long. In spite of this diversity, the phylum Mollusca (L. molluscus, soft) is not difficult to characterize Characteristics of the phylum Mollusca include: 1. Body of two parts: head-foot and visceral mass 2. Mantle that secretes a calcareous shell and covers the visceral mass 6 Dr. Muhammad Moosa Abro Phylum Mollusca
- 7. MOLLUSCAN CHARACTERISTICS 3. Mantle cavity functions in excretion, gas exchange, elimination of digestive wastes, and release of reproductive products 4. Bilateral symmetry 5. Trochophore larvae, spiral cleavage, and schizocoelous Coelom formation 6. Coelom reduced to cavities surrounding the heart, nephridia,and gonads 7. Open circulatory system in all but one class (Cephalopoda) 8. Radula usually present and used in scraping food 7 Dr. Muhammad Moosa Abro Phylum Mollusca
- 8. The body of a mollusc has two main regions—the head-foot and the visceral mass (figure 11.2). The head-foot is elongate with an anterior head, containing the mouth and certain nervous and sensory structures, and an elongate foot, used for attachment and locomotion. The visceral mass contains the organs of digestion, circulation, reproduction, and excretion and is positioned dorsal to the head-foot. 8 Dr. Muhammad Moosa Abro Phylum Mollusca MOLLUSCAN CHARACTERISTICS
- 9. The mantle of a mollusc usually attaches to the visceral mass, enfolds most of the body, and may secrete a shell that overlies the mantle. The shell of a mollusc is secreted in three layers (figure 11.3). 9 Dr. Muhammad Moosa Abro Phylum Mollusca The outer layer of the shell is called the periostracum. Mantle cells at the mantle’s outer margin secrete this protein layer. The middle layer of the shell, called the prismatic layer, is the thickest of the three layers and consists of calcium carbonate mixed with organic materials. Cells at the mantle’s outer margin also secrete this layer. The inner layer of the shell, the nacreous layer, forms from thin sheets of calcium carbonate alternating with organic matter. Cells along the entire epithelial border of the mantle secrete the nacreous layer. Nacre secretion thickens the shell. MOLLUSCAN CHARACTERISTICS
- 10. Between the mantle and the foot is a space called the mantle cavity. The mantle cavity opens to the outside and functions in gas exchange, excretion, elimination of digestive wastes, and release of reproductive products. 10 Dr. Muhammad Moosa Abro Phylum Mollusca
- 11. 11 The mouth of most molluscs possesses a rasping structure called a radula, which consists of a chitinous belt and rows of posteriorly curved teeth. The radula overlies a fleshy, tonguelike structure supported by a cartilaginous odontophore. Muscles associated with the odontophore permit the radula to be protruded from the mouth. Muscles associated with the radula move the radula back and forth over the odontophore. Food is scraped from a substrate and passed posteriorly to the digestive tract. Dr. Muhammad Moosa Abro Phylum Mollusca MOLLUSCAN CHARACTERISTICS
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- 13. References 13 1. Miller, A.S. and Harley, J.B. ; 1999 , 2002., 2007, 2009, 2012 & 2016 Zoology, 4th , 5th, 6th, 7th, 8th , 9th& 10th Edition (International), Singapore : McGraw Hill. 2. Hickman, C.P., Roberts, L.C/, AND Larson, A., 2018. INTEGRATED PRINCIPLES OF ZOOLOGY, 15th Edition (International), Singapore: McGRAW-Hill