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Molluscs

Molluscs. Snails, Clams, Octopuses, Squid – the Phylum Mollusca Second largest Phyla behind Arthropoda. General Characteristics. Many are benthic Complete digestive tract Open circulatory system Usually separate sexes Cephalization Soft bodies; mantle secretes shell. Class Gastropoda.

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Molluscs

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  1. Molluscs Snails, Clams, Octopuses, Squid – the Phylum Mollusca Second largest Phyla behind Arthropoda

  2. General Characteristics • Many are benthic • Complete digestive tract • Open circulatory system • Usually separate sexes • Cephalization • Soft bodies; mantle secretes shell

  3. Class Gastropoda • Gastro = stomach, Pod = foot • Bodies covered by one shell • Most are benthic, herbivores • Radula contains a ribbon of flexible teeth – scrapes surfaces for algae or to cut into other shells • Snails, whelks, abalone, nudibranch, conch

  4. The Gastropods

  5. Class Pelecypoda • Two footed, two shells (valves) • Benthic, planktivores • Filter sea water through incurrent and excurrent siphon • Some sessile ( oyster) • Swimmers (Scallop) • Clams, oyster, scallop, coquina

  6. The Bivalves

  7. Class: Cephalopoda • Cephalo = head, pod = foot • Internal, clear, flexible shell • Hard beak • Most advanced brain of all invertebrates • Shy and hide in small spaces.

  8. Characteristics • Head with 8 regenerative Arms and 2 Tentacles • Mouth has a sharp beak • Moves by “jet propulsion” • Chromatophores in the skin change colors when alarmed or camouflaged • Ink gland used to escape • Eyes have cornea, lens and retina, excellent vision • Octopus has internal fertilization, sperm transferred into female’s mantle. • Female cleans, aerates and watches eggs for 30 days and usually dies after hatching

  9. Chitons • All Marine • Eight overlapping shell plates • Restricted to rocky shores

  10. Tusk Shells: scaphopods • Elongated shell, open at both ends • Live in sandy or muddy bottoms • Most common in deep water.

  11. Monoplacophorans • Limpet-like molluscs • Considered a “living fossil”

  12. Ecology • Occupy all marine habitats • Thrive on any diet • Tolerate high levels of pollution (bivalves)

  13. Mollusca (snails, clams, octopuses, tusk shells, chitons, etc.) • ..Coelomate, bilaterally symmetrical (secondary asymmetry) • ..Principle body cavity a hemocoel • ..Mantle covers body (thickened epidermis which secretes the shell, when present) • ..Shell made of calcareuos material • ..Muscular foot • ..Buccal region with radula • ..Complete gut

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