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Molluscs and Annelids

Molluscs and Annelids. (Mollusks) https://www.southplainscollege.edu/biology/swages/HICKMAN%20PP/MOLLUSCS_files/frame.htm. PHYLUM MOLLUSCA. THE MOLLUSCS . 2. What is a mollusk?. Basic answer: Slugs, snails, and animals that once lived in shells in the ocean or on the beach are all mollusks.

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Molluscs and Annelids

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  1. Molluscs and Annelids (Mollusks) https://www.southplainscollege.edu/biology/swages/HICKMAN%20PP/MOLLUSCS_files/frame.htm

  2. PHYLUM MOLLUSCA THE MOLLUSCS 2

  3. What is a mollusk? • Basic answer: • Slugs, snails, and animals that once lived in shells in the ocean or on the beach are all mollusks.

  4. INTRODUCTION • Mollusca means “soft.” Most molluscs have shells for protection • Eight diverse classes of molluscs with more than 100,000 named species • Includes snails, clams, squids, octopuses, nautiluses, etc • Found in almost all habitats. The need for calcium is a major limiting factor

  5. Characteristics of Mollusk: • An advanced nervous system • Many types of feeders, including, carnivores, herbivores, filter-feeders and grazers. All but one class have a radula, a ribbon-like structure with teeth of chitin that scrapes, cuts or tears food • Most molluscs are dioecious. They have a free-swimming trochophore larva; many also have a veliger larva stage

  6. CHARACTERISTICS, Cont. • An advanced nervous system • Many types of feeders, including, carnivores, herbivores, filter-feeders and grazers. All but one class have a radula, a ribbon-like structure with teeth of chitin that scrapes, cuts or tears food • Most molluscs are dioecious. They have a free-swimming trochophore larva; many also have a veliger larva stage

  7. CHARACTERISTICS, Cont. • Durable shells • found in marine, freshwater, and terrestrial habitats • One of the most successful of all phyla – only arthopods have more terrestrial species • Important food source for humans • Coelom – very important • 2 body opeings

  8. Economic importance • – pearls mother –of –pearl jewelry and other jewelry • Food source • Not entirely beneficial • - shipworms – destructive to timber submerged in sea • slugs, terrestrial snails can cause extensive damage to flowers, gardens an crops • hosts to intermediate stages for many serious diseases

  9. Body size

  10. External body plan • Some mollusks have shells • Some are adapted to live without a hard covering (slugs and squids) • Bivalve – 2 shelled mollusks (clams oysters, scallops)

  11. External body plan - bivalve • Umbo • Growth lines • Ventral side – • Dorsal side

  12. UMBO tells direction Anterior Posterior Dorsal Ventral

  13. NO CEPHALIZATION (No head) Shell = valve (Bivalves = 2 shells) Growth rings Adults = sessile (stay in one place)

  14. Distinct bilateral symmetry Visceral mass Muscular foot Mantle gills Siphon Exhalent Inhalent Adductor muscle Internal body plan - bivalve

  15. THE MOLLUSCS 15

  16. VISCERAL MASS Contains heart, digestive, excretory, reproductive

  17. INCURRENT & EXCURRENTSIPHONS move food up toward mouth CILIA on gills pull in water

  18. Describe the function of gills

  19. GILLS Trap food (PALPS move it forward) Ridges for more surface area (like typholosole) Gas exchange Diffusion moves oxygen & carbon dioxide across membrane

  20. Mollusc shell • Secreted by mantle • Protects the 2 underlying layers form erosion • Pearls

  21. THE MOLLUSCS 22

  22. Describe the different functions of the mantle • ( include the role of the continuous stream of water) • Some molluscs can withdraw into mantle davity for protection • In aquatic molluscs a continuous stream of water is passed into and out of this cavity by the cilia on the gills • This action brings in oxygen and in the case of bivalves food • Carries out waste material • In squids and octopuses the mantle cavity has been modified to create the jet propulsion system that enables these animals to move rapidly through the water.

  23. ADDUCTOR MUSCLES Turn POSTERIOR END toward doorCut your adductor muscles to open shell

  24. Functions of the foot

  25. Describe how molluscs obtain food

  26. Circulatory system in molluscs • Open system of circulation • Closed circulatory system • heart

  27. OPEN CIRCULATION • Blood flows loose inside coelom and tissue spaces • Reduced Coelom = pericardial cavity (space around heart)

  28. Excretion in molluscs • REFER TO PREVIOUS DIAGRAM

  29. Respiration in molluscs

  30. NERVOUS SYSTEM https://www.student.loretto.org/zoology/Graphic%20webs/Clam-%20nervous%20system.htm 3 pairs of ganglia 2 pairs of nerve cords

  31. Reproduction in Molluscs TROCHOPHORE LARVA VELIGER LARVA BACK THE MOLLUSCS 32

  32. CLASSIFICATION • Of the 8 mollusc classes, we’ll look at 3: • Class Polyplacophora- the chitons • Class Scaphopoda- the tooth shells • Class Gastropoda- the snails • Class Bivalvia- the clams, oysters • Class Cephalopoda- octopuses, squids

  33. Three main classes of molluscs

  34. Gastropoda

  35. CLASS GASTROPODA • The snails, slugs, whelks, limpets, conchs, periwinkles and others • Largest, most diverse group of molluscs • One-piece shell, usually coiled • Mostly herbivores; radula for feeding • Land and freshwater gastropods have lungs

  36. THE MOLLUSCS 37

  37. THE MOLLUSCS 38

  38. THE MOLLUSCS 39 SEA SLUG: CLASS GASTROPODA

  39. Bivalvia

  40. CLASS BIVALVIA • Have 2 shells • Includes clams, oysters, scallops and mussels • Sedentary filter-feeders. The only molluscan group with no radula

  41. THE MOLLUSCS 42 A GIANT CLAM

  42. THE MOLLUSCS 43

  43. Cephalopoda

  44. CLASS CEPHALOPODA • The squids, octopuses and nautiluses • Among the most advanced of all invertebrates • Active predators living in the ocean, which requires them to be fast, smart, coordinated and possess good eyesight • They have a funnel-like structure allowing for movement by jet propulsion • Arms and/or tentacles for grasping. The tentacles have suckers

  45. CEPHALOPOD SHELLS • Only the members of the genus Nautilus possess an external shell. Unlike the shells of gastropods nautiloid shellsare divided by septa into a series of chambers. The animal lives only in the outer chamber • Cuttlefish have an internal chambered shell • Squids have a small internal sheet-like shell • Octopuses have no shell

  46. CEPHALOPOD EYESIGHT • Nautiloids have relatively poor eyesight compared to other cephalopods • Other cephalopods have image-forming eyes similar to mammals, but they evolved separately (convergent evolution). Cephalopod eyes possess structures similar to mammalian eyes, but they focus differently

  47. THE MOLLUSCS 48

  48. SQUID THE MOLLUSCS 49

  49. THE MOLLUSCS 50 AN OCTOPUS

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