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Download Phylum Mollusca - Bakersfield College
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Kingdom Animalia Subkingdom Eumetazoa Bilateria Phylum Mollusca Professor Andrea Garrison Biology 3A Illustrations ©2014 Cengage Learning unless otherwise noted Phylum Mollusca • Molluscs (mollis = soft) • Chitons, clams, tusk shells, snails, octopods. Mollusca; tusk shell photo ©BIODIDAC, http://creativecommons.org/licenses/by-nc/4.0/ 2 Phylum Mollusca • Marine, freshwater, moist terrestrial habitats • Free-living • Wide range of feeding styles – Scrape plant material – Filter microscopic organisms – Predators • Triploblastic • Protostomes • Bilateral w/cephalization Mollusca 3 Phylum Mollusca • Trochophore larvae – Embryological development results in trochophore – May be followed by veliger stage before metamorphosing into adult Mollusca 4 Phylum Mollusca • Coelomates – Coelom reduced to area around heart, gonads • 1-2 metanephridia • 2 ventral nerve cords w/paired ganglia • Most with exoskeleton (shell) secreted from epithelial mantle • 3 body regions – Head – Foot – Visceral mass Mollusca 5 Phylum Mollusca • 3 body regions – Head well developed • Mouth w/ radula for scraping food or drilling through shell of prey • Sensory structures – Eyes, tentacles – Muscular ventral foot • Locomotion • May be modified – Visceral mass • Major organs Mollusca 6 Phylum Mollusca • Mantle – Part of dorsal body wall • Encloses visceral mass • Secretes shell – Usually calcium carbonate • Defines separate mantle cavity – Houses gills or lung – Aquatic species– cilia create water currents into mantle cavity Mollusca 7 Phylum Mollusca • Size requires circulatory system • Open circulatory system – Blood vessels from heart open into sinuses and bathe tissues directly – Sinuses drained by vessels that return “blood” back to heart – Molluscan “blood” is hemolymph Mollusca 8 Molluscan Body Plans Mollusca 9 Phylum Mollusca • 5 common classes – Polyplacophora; chitons – Scaphopoda; tusk shells – Gastropods; snails – Bivalvia; clams, mussels – Cephalopoda; octopods, squid, chambered nautiluses Mollusca 10 Class Polyplacophora • Chitons (poly = many; plax = flat surface) • Sedentary • Anchors to rocks • Dorsal shell divided into 8 plates – Allows it to conform to curvature of rocks and get good suction • Dioecious Mollusca 11 Class Gastropoda • Snails and slugs (gaster = belly; podos = foot) • Most abundant class – ~40,000 species • Herbivores or predators – Herbivores scraped algae or plants with radula – Predators use radula to “drill” through shell of prey or radula modified as harpoon with poison Conus geographicus Mollusca; photo by Kerry Matz, National Institute of General Medical Services http://www.nigms.nih.gov/news/findings/sept02/snails.html 12 Class Gastropoda • Head with sensory structures – Tentacles have chemical and touch receptors – Eyes light sensitive (not image forming) • Hermaphroditic or dioecious Mollusca 13 Class Gastropoda • Most with coiled shell • Larval torsion (not related to coiled shell) – During larval state, visceral mass rotates 180o so mantle cavity rests right above head – Head can withdraw into mantle cavity – Foot pulls up behind • In marine snails, foot often has operculum to close off shell Mollusca 14 Class Bivalvia • Clams, mussels, scallops (bi = two; valva = folding door) • Aquatic; most marine • Some anchored to rocks – Mussels, oysters • Some mobile – Clams – Use foot to burrow in sand or mud Tridacna gigas Mollusca; photo by Christoph Specjalski; http://commons.wikimedia.org/wiki/Commons:GNU_Free_Documentation_License,_version_1.2 15 Class Bivalvia • Two shells – Hinged dorsally w/elastic ligament – Ligament holds shell open – 1-2 adductor muscles contract to close shell • Mantle cavity inside shells – Lined by mantle, which secretes shells • Two siphons – Incurrent siphon brings water into shells and over gills – Excurrent siphon removes water and wastes from shell Mollusca 16 Class Bivalvia • No head • No radula • Gills w/cilia and mucus – Traps food particles and moves them to mouth • Palps assist food to mouth • Filters bacteria, phytoplankton, detritus Mollusca 17 Class Cephalopoda • Octopods, squids, chambered nautiluses (kephale = head; podos = foot) • Marine • Well-developed head – Image-forming eyes – Brain • Very intelligent • Shell – External—nautiluses – Internal—squid – Lacking—octopods Mollusca 18 Class Cephalopoda • Foot modified as siphon and arms and tentacles with suckers – Siphon used for jet propulsion • Very fast – Arms may be used for movement • Mouth w/beak in center of arms • Radula helps food move to back of esophagus • Camouflage – Skin color and texture – Ink cloud released through siphon • Dioecious Mollusca 19 Aquatic Respiratory Organs Gills Mollusca 20 Terrestrial Respiratory Organs Trachea Lungs Mollusca 21
