Mollusca Lecture Notes PDF

Platyhelminthes 26 Phyla of Bilaterally Symmetrical Invertebrates Gastrotricha "Ecdysozoa"...

Platyhelminthes 26 Phyla of Bilaterally Symmetrical Invertebrates Gastrotricha "Ecdysozoa" Annelida Mollusca Nemertea Oviparous Direct development Dioecious Indirect development Coelom Platyhelminthes 26 Phyla of Bilaterally Symmtrical Invertebrates Gastrotricha "Ecdysozoa" Annelida Mollusca Nemertea Oviparous Direct development Dioecious Indirect development Coelom  Cephalopoda – Pelagic and exclusively predatory Molluscs show a lot more diversity in body shape, trophic ecology, and habitat thany any group that existed prior to them Bivalvia: endobenthic filter feeders Polyplacophora Benthic herbivores Gastropoda: Benthic omnivores predators and herbivores Ancestral Mollusc (wormy, benthic, marine predator) Aplacophoran Mollusc  Phylum Mollusca >150,000 species (huge fossil record) Coverage 1. Introduction to defining characteristics 2. Introduce the Classes (only 3 will be examined in detail) 3. Shell Structure and Diversity 4. Class Gastropoda – snails and slugs Morphology Evolution of Terrestriality and loss of the shell 5. Class Bivalvia – clams, oysters Endobenthic lifestyle 6. Class Cephalopoda – squids, octopods Morphology Evolution Ecology Phylum Mollusca >150,000 species (huge fossil record) Mollusc = soft body (Latin)  Phylum Mollusca >150,000 species (huge fossil record) 1. Primitively marine and worm-like 2. Coelomate Possess a coelom zygote v age c le a  Embryogenesis coeloms mesoderm Blastopore = mouth in "protostomes" Archenteron = divestive tract Ectoderm - epidermis and nervous system in larvae and adults Mesoderm - muscles, gonads , coeloms Endoderm - digestive epithelium in larvae and adults Mesoderm forms many tissues and organs – some of those organs are coeloms = hollow cavities of mesoderm (2 or more) 1. Lined by a mesothelium Contractile epithelium 2. Coeloms full of coelomic fluid (similar to seawater) act as fluid filled bags = hydrostatic skeleton Functions of coelom vary by taxa 1. Function in locomotion (Annelida) 2. Function for circulation (Mollusca) 3. Function for excretion (Mollusca)  Phylum Mollusca >150,000 species (huge fossil record) 1. Primitively marine and worm-like 2. Coelom coelom is reduced to a cavity around the heart = (pericardial coelom) 3. Single 3-chambered heart Functions in circulation (nutrients, oxygen) and excretion (ammonia) 4. Hemocoel = body cavity where blood bathes the internal organs (not a coelom) ”open” circulatory system = not all blood is contained in vessels 5. Ctenidia – gills for respiration: necessary because of large body size Connect heart, hemocoel, and ctenidia  Phylum Mollusca >150,000 species (huge fossil record) 6. Mantle cavity – an open space where ctenidia are exposed to the environment cavity also contains anus (defecation), gonopores (gametes leave the body), nephridiopores (for excretion) Scallops can eject water from their mantle cavity to swim Ventral foot Cephalopods can eject water from their mantle cavity to swim  Phylum Mollusca >150,000 species (huge fossil record) 7. Mantle = glandular dorsal epidermis  Phylum Mollusca >150,000 species (huge fossil record) 7. Mantle = glandular dorsal epidermis Glands (shell glands) secrete hard structures (Protein + CaCO3) Shells are not a synapomorphy of Mollusca Shells are derived within the phylum Plates Shell Scales/spines Shell Shell  Phylum Mollusca >150,000 species (huge fossil record) 8. Ventral foot – region specialized for locomotion Ventral foot Ciliated in aquatic sp No cilia in terrestrial sp Most bivalves live beneath the substrate Foot is used for burrowing Ventral foot  Cephalopods – squid, octopus, Nautilus Ventral foot is modified into tentacles or arms  Phylum Mollusca >150,000 species (huge fossil record) 9. Complete digestive tract Mouth contains a Radula – tongue-like organ with teeth  Phylum Mollusca >150,000 species (huge fossil record) 9. Complete digestive tract Mouth contains a Radula – tongue-like organ with teeth  Phylum Mollusca >150,000 species (huge fossil record) 10. Excretory organs = Metanephridia (shared with Phylum Annelida) Connected to their heart Found only in adults Larvae have protonephridia 11. Dioecious (hermaphroditism is present in terrestrial species) 12. Indirect development (larva in the lifecycle of most species) 13. Ancestrally Marine – FW and terrestrial are derived