12. Mollusca I Oct 12

12. Mollusca I Oct 12 - Phylum Mollusca snails, clams,...

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Unformatted text preview: Phylum Mollusca snails, clams, squids, octopus, chitons & friends 2nd largest phylum > 150,000 extant species > 50,000 fossil species Triploblastic Organ Grade Coelomate - Schizocoely - but reduced in adult Coelomate Protostomes Shared Ancestral Characters Similar basic body plan 4 Basic Body Regions: Head - cephalized Foot - muscular Visceral Mass - dorsal extension from body Mantle - cover viscera, secrete shell creates mantle cavity Head Head mouth + accessory feeding structures e.g., radula, jaws e.g., radula Sensory Structures cephalic tentacles eyes Cerebral ganglia 1 Foot Generally muscular can be very large used for crawling, burrowing secreting attachment ancestral probably flat - creeping ancestral Visceral Mass Dorsal extension of body contains major organ systems digestive reproductive circulatory excretory Mantle Covers visceral mass Secretes Shell Forms Mantle Cavity openings of: gonoducts openings gonoducts excretory system anus paired gills = diagnositc of phylum paired of = Ctenidia (singular Ctenidia (singular ctenidum) ctenidum Ctenidium 3 derivatives of larval coelom seen in adults: derivatives seen 1. Pericardial cavity - surrounds heart 1. 2. Gonads 3. Excretory organs (Renal organs, kidneys) coelomoducts originally probably served as both for nitrogenous waste and gonoducts for gonoducts Excretory Systems Remove nitrogenous waste Other functions: osmoregulation – water balance release gametes e.g., polychaetes Ducts remove waste outside body close association with coelomic fluid and/or circulatory system 2 Some extant molluscs show nice Some show linear arrangement of body linear ( Anterior - Posterior, Longitudinal Axis) Anterior however most do not Many organized around a Dorsoventral Body Axis Gastropods - TORSION Gastropods TORSION will come back to this will Unsegmented Cephalized cerebral ganglia (+ other major ganglia in body) Shell Secreted by mantle Coelom very reduced in adult Coelom pericardial cavity ducts of gonads kidney ducts Muscular body wall 3 Multilayered periostracum - outer organic covering prismatic - middle, crystalline, calcite nacreous - inner, sheet like crystal calcite Mantle Cavity and Ctenidia Mantle Ctenidia extent varies Place to hang your ctenidia Place ctenidia Respiratory Chamber (terrestrial molluscs) Respiratory molluscs Chamber for moving water getting rid of waste, gametes Chamber for feeding Digestive System Buccal Mass (muscles, aux. strucutres, mouth) Buccal cavity Radula chitinous ribbon, rows of teeth used for feeding Esophagus (but not in bivalves) Stomach a) sorting, b) grinding, c) digestion crystalline style - digestive enzymes Digestive glad - absorption, storage organ Hind gut with terminal anus Ctenidium Circulatory System - OPEN Coelom Coelom large in larva large reduced in adult remnants: remnants: gonads gonads pericardial cavity ceolomoducts/kidneys Heart, arteries Haemocoel – major body cavity (exception - cephalopods) Hydrostatic skeleton use incompressibility of fluids to generate forces to antagonize muscles and support body pigmented, hemocyanin, may also have hemoglobin 4 Excretory System Usually laterally paired metanephridia = kidneys Nervous System Circumentric nerve ring 2 pairs of nerve cords Foot Viscera & Mantle Decentralized control - several major ganglia Reproductive System Usually dioecious Primitive condition free spawn, ext. fertilization Derived retain eggs, brood copulate hermaphroditic Trochophore Larva - tiny eggs, short development Trochophore Veliger Larva - large fused cilia on lobes (velar Veliger large lobes) for swimming and feeding, shell lobes) trochophore veliger Indirect life history 5 Feeding Specializations All types of feeding Detritus – deposit Herbivores Predators Specializations of the radula for feeding material shape use The radula is the major feeding structure for molluscs except bivalves. 6 Among species Tooth shape correlated with diet Tooth shape affects performance in different environments (feeding on different types of food) 7 Radular teeth made of different materials Radular teeth Iron teeth Wood Iron teeth Calcium carbonate 8 Chitin Excavating Chitin Brush like Feeding on Sponges Conus Specialized predator Uses toxins Spears prey with hypodermic – like radular tooth Predator – Tears flesh with radula 9 ...
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