Mollusca BIO205 PDF

Phylum Mollusca Chapter 10  METAZOA Bilateria Protostomia Deuterostomia...

Phylum Mollusca Chapter 10  METAZOA Bilateria Protostomia Deuterostomia Lophotrochozoa Ecdysozoa choanofla gellates sponges cnidarians molluscs annelids flatworms nematodes arthropods echinoderms chordates Trochophore larva Mouth formed from blastopore, etc. (Org. & Syst. level) Gastrulation Bilateral symmetry Diploblasty Cephalization Triploblasty Multicellularity Blastulation Mollusca Spiral cleavage Mosaic embryo Blastopore becomes mouth Triploblasty Bilateral symmetry Cephalization Reminder: Body cavities (gut + cavity around the gut) Through embryonic development, the blastocoel of triploblasts can: c) be replaced by the true coelom (cavity forms inside the mesoderm) Triploblastic coelomate A true coelom found in earthworms, molluscs, chordates and most phyla (15- 20) Reminder: Body cavities (gut + cavity around the gut) Through embryonic development, the blastocoel of triploblasts can: c) be replaced by the true coelom (cavity forms inside the mesoderm) A true coelom found in earthworms, molluscs, chordates and most phyla (15- 20)  Phylum Mollusca “Soft animals” 90K named living spp.; 70K fossil spp. Very important size range Majority free-living, few parasites Ecologically diverse, marine, freshwater, and terrestrial Filter-feeders, carnivores and herbivorous grazers Mono or dioecious, w/without copulation  Phylum Mollusca Diverse body plans reflecting diverse lifestyles Ex: variable degrees of cephalization Ex: presence or absence of calcium carbonate shell Squids Chitons Snails Clams Octopuses Slugs Oysters Nautiluses Mussels Cuttlefishes  “Generalized” mollusc 2 main body parts: head-foot and visceral mass - Feeding - Digestion - Locomotion - Circulation - Sensory organs - Respiration - Reproduction  Phylum Mollusca Synapomorphies: 1) radula: rasping organ used in feeding (lost in bivalves)  (supporting cartilage) Ribbon-like Radula membrane à Treadmill (or Rasping, protrusible, tongue-like escalator) organ In all molluscs except bivalves  Phylum Mollusca Synapomorphies: 1) radula: rasping organ used in feeding (lost in bivalves) 2) mantle: sheath of skin extending from dorsal body wall. Mantle secretes the shell and forms mantle cavity housing gills (or lungs) Mantle and mantle cavity Mantle and mantle cavity Mantle and mantle cavity  Phylum Mollusca Synapomorphies: 1) radula: rasping organ used in feeding (lost in bivalves) 2) mantle: sheath of skin extending from dorsal body wall and secreting shell also forms mantle cavity à houses gills (or lungs).  METAZOA Bilateria Protostomia Deuterostomia Lophotrochozoa Ecdysozoa choanofla gellates sponges cnidarians molluscs annelids flatworms nematodes arthropods echinoderms chordates Radula & mantle Trochophore larva Mouth formed from blastopore, etc. (Org. & Syst. level) Gastrulation Bilateral symmetry Diploblasty Cephalization Triploblasty Multicellularity Blastulation Diversity of body plans MANTLE CAVITY GASTROPODS CHITONS Diversity of body plans MANTLE CAVITY GASTROPODS CHITONS Diversity of body plans MANTLE CAVITY GASTROPODS CHITONS Diversity of body plans MANTLE CAVITY GASTROPODS CHITONS Diversity of body plans MANTLE CAVITY GASTROPODS CHITONS  Phylum Mollusca Digestive system: Complete Complexe Highly specialized for specific feeding habits Extracellular digestion in stomach, absorption in intestine  Phylum Mollusca Reduced coelom Open circulatory system = pericardiac cavity (closed in cephalopods) 3 chambered heart 1 muscular ventricle 2 atria Simple Open  Phylum Mollusca Circulatory system: 3 chambered heart 1 muscular ventricle 2 atria Simple Open Circulatory system & coelom are fused = Hemocoel Hemocoel Bivalves Gills  (sinus = cavity or space in tissues) Few open ended vessels Organs bathed directly in blood Blood entirely enclosed in vessels (hemolymph) Exchange with organs through capillary Large sinuses form hemocoel (cavity) beds Blood circulation slow = less efficient Blood circulation fast = more efficient 25  Phylum Mollusca Respiratory system: Most have gills (or lung) linked to circulatory system for gas exchange Water flow over gills created by movement of gill cilia Importance of the mantle cavity: Protects gills Keeps humidity Mantle also involved in gas exchange Note: mantle is also involved in passive gas exchange Phylum Mollusca Gills Oxygen exchange between water and gill (% indicate saturation levels) Oxygen exchange between water and gill Most gills are designed so that the flow of water over the surface runs in the direction opposite to blood flow (counter- current exchange) Oxygen exchange between water and gill 30 Oxygen exchange between water and gill  Phylum Mollusca Excretory system: 1 pair of metanephridia. Nephridiopore More complex and efficient than protonephridia of Platyhelminthes (controls osmolarity and nitrogenous wastes) Note: mantle is also involved in excretion Platyhelminthes protonephridium Protonephridium: a type of primitive nephridium. Wastes = ammonia (NH3) Nitrogenous wastes Ammonia Urea Uric acid NH3 CO(NH2)2 C5H4N4O3 Most toxic Least toxic Platyhelminthes Molluscs (most)  Excretory system (Mollusca) Metanephridium: a type of nephridium in which the inner end opens into the coelom Waste = ammonia (NH3) 1 of a pair of metanephridia  Phylum Mollusca Nervous system: Many pairs of ganglia, connected by nerve cords Many specialized sensory organs Cephalization in some  Reproduction Most dioecious (some monoecious, especially in Gastropoda) Life cycle direct or indirect Zygote (fertilized egg) immature adult  Reproduction Most dioecious (some monoecious) NO asexual reproduction Life cycle direct or indirect  Reproduction Most dioecious (some monoecious) Life cycle direct or indirect No asexual reproduction (few exceptions in Gastropoda) With or without copulation Mollusc classes Class Solenogastres Class Polyplacophora Class Gastropoda Class Cephalopoda Class Caudofoveata Class Monoplacophora Class Bivalvia Class Scaphopoda Animalia Molluscs Gastropoda, Cephalopoda, Bivalvia, Polyplacophora 42 43  Class Polyplacophora 800 marine, most shore dwellers Shell forms 7-8 plates 2 lateral mantle cavities with gills Use radula to scrape algae off rocks Mostly dioecious with trochophore larva, no copulation (external fertilization) Trochophore larva juvenile nacre 45  Class Gastropoda 70 K living species Marine, freshwater, terrestrial Mostly monoecious with copulation, trochophore larva present in most Shell present, reduced or lost Most secondarily asymmetrical due to torsion Gastropoda Torsion: twisting of visceral mass, nerve cord and mantle cavity relative to foot and head Generalized mollusc Gastropods 47 Torsion: twisting of visceral mass, nerve cord and mantle cavity relative to foot and head Mouth Mouth Anus Mouth Anus Mantle Anus cavity Advantage: head can be retracted first Problem?: FOULING Gastropoda Coiling FOULING 49 Gastropoda Coiling: Leads to more compact, efficient use of space Animal becomes bilaterally asymmetrical In this case, the gills and metanephridium are lost on the right side Reduces fouling problem Some taxa have ‘’detorted’’ (ex: sea slugs) 50 Gastropoda Anus Gill Water flow 51  Digestive system Radula Herbivorous Rasping algae from substrate Break off pieces of seaweeds Moon snail Naticarius orientalis Scavengers Carnivorous Gas exchange in terrestrial gastropods  Gas exchange in sea slugs Some have lost their gills: Gas exchange through skin Highly ramified body surface Why?  Reproduction in Gastropoda Mostly monoecious with copulation Mollusc video #3: https://www.youtube.com/watch?v=wG9qpZ89qzc 56  Squid Nautilus Class Cephalopoda Octopus Cuttlefish Class Cephalopoda = head and foot 600 marine species 2-3 cm to 18m Giant squid  Class Cephalopoda 600 marine species All predaceous with radula and jaws, some with poison glands Dioecious with “copulation”, direct development Shell external and coiled in nautilus, internalized or absent others Very active animals (mostly pelagic) Closed circulatory system Largest invertebrate brain, complex eyes Cephalopod body plan Anterior view Cephalopod body plan (= gill) Lateral view Cephalopoda Predators à digestive and nervous system 62 Digestive system à Predators Mouth: - Strong beaklike jaws - Radula in the middle to tears off pieces of flesh Digestive system à Predators Arms: - Complex musculature - Used to catch and manipulate preys - Used for locomotion in octopuses  Class Cephalopoda Very active animals Closed circulatory system Swim by forcing water from mantle cavity through a funnel Systemic heart  Class Cephalopoda “Smart” animals largest invertebrate brain complex eyes visual communication Cephalopoda Parallelism between cephalopod and vertebrate eye convergent evolution cornea iris blind spot lense retina 67  Parallelism between cephalopod and vertebrate eye convergent evolution Outgrowth of the brain cornea iris blind spot lense retina Ingrowth of epidermis Skeletal system à Where is the shell? Shell: - Ancestor had a shell Skeletal system à Where is the shell? Shell: - Ancestor had a shell Lost in some Coiled in some (octopuses) (nautiluses) Skeletal system à Where is the shell? Shell: - Ancestor had a shell pen Internal in some (squids)  Space filled Cephalopod shell with gas Nautilus internal anatomy 72  Squid copulation Dioecious with copulation zygote Direct development immature adult Paul the Octopus Soccer Oracle 2008-2010 75  Class Bivalvia 8K aquatic species Most are sessile filter feeders; benthic habitats No radula, reduced cephalization Two shells (valves) hinged dorsally, held shut by adductor muscles Animal laterally flattened between two valves Most dioecious, no copulation Bivalve body plan Bivalve body plan Dorsal Ventral Bivalvia Filter feeders à Respiratory / Digestive system: Dorsal Right valve Posterior adductor muscle Posterior TWO OPENINGS Anterior Ventral 79 Lateral view of left side of freshwater clam Bivalvia Excurrent Incurrent siphon siphon 80 Bivalvia Digestive system: 81 Left mantle and gill removed Bivalvia Generalized bivalve reproduction External fertilization Gametes shed through excurrent opening Most dioecious, no copulation 82 Bivalve sensory structures Aequipecten irradens  Phylum Mollusca What’s new: Circulatory system more complex Heart more complex (ventricle & 2 atria) Complete digestive tract, with stomach Respiratory system more complex, with gills Cephalopoda: Most complex brain in in vertebrates Closed circulatory system Complex muscular system Skeletal system ?