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Marine Molluscs: Diversity and Ecology

Explore the fascinating world of marine Mollusca, including snails, clams, and octopuses. Learn about their unique characteristics, diverse habitats, and ecological roles. Discover the astonishing diversity within this phylum and their adaptation strategies to thrive in various marine environments.

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Marine Molluscs: Diversity and Ecology

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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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