1. 16-1 CHAPTER 16 MolluscsMolluscs

2. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 16-2 Fluted Giant Clam

3. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 16-3 Characteristics Phylum Mollusca Over 90,000 living species and 70,000 fossil species Over 90,000 living species and 70,000 fossil species Soft body and protostomes Soft body and protostomes Include chitons, tusk shells, snails, slugs, nudibranchs, clams, mussels, oysters, squids, octopuses, and nautiluses Include chitons, tusk shells, snails, slugs, nudibranchs, clams, mussels, oysters, squids, octopuses, and nautiluses

4. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 16-4 Chiton Marine SnailNudibranch Pacific Giant Clam Octopus

5. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 16-5 Characteristics: Herbivorous grazers, predaceous carnivores, filter feeders, and parasites Herbivorous grazers, predaceous carnivores, filter feeders, and parasites Most are marine, but some are terrestrial or freshwater aquatic Most are marine, but some are terrestrial or freshwater aquatic Characteristics

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7. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 16-7 Evolution Fossil evidence Fossil evidence Indicates molluscs evolved in the sea Indicates molluscs evolved in the sea Most have remained marine Most have remained marine Some bivalves and gastropods Some bivalves and gastropods Moved to brackish and freshwater Moved to brackish and freshwater Snails (gastropods) successfully invaded land Snails (gastropods) successfully invaded land Limited to moist, sheltered habitats with calcium in the soil Limited to moist, sheltered habitats with calcium in the soil Cephalopods Cephalopods Evolved to become relatively intelligent Evolved to become relatively intelligent Characteristics

8. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 16-8 Economics Many are used as food Many are used as food Culturing of pearls is an important industry Culturing of pearls is an important industry Snails and slugs are garden pests Snails and slugs are garden pests Characteristics

9. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 16-9 Form and Function Mollusc Body Plan: Head-Foot and Visceral Mass Portions Head-foot region contains feeding, sensory, and locomotor organs (foot) Head-foot region contains feeding, sensory, and locomotor organs (foot) Visceral mass contains digestive, circulatory, and reproductive organs Visceral mass contains digestive, circulatory, and reproductive organs Mantle Cavity Mantle Cavity Space between mantle (sheath of skin) and body wall is the mantle cavity Space between mantle (sheath of skin) and body wall is the mantle cavity Mantle cavity houses the gills or a lung Mantle cavity houses the gills or a lung In most molluscs In most molluscs Mantle secretes a shell over the visceral mass Mantle secretes a shell over the visceral mass

10. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 16-10 Generalized Mollusk Anatomy

11. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 16-11 Radula Radula Unique to molluscs Unique to molluscs Found in all except bivalves Found in all except bivalves Protruding, rasping, tongue-like organ Protruding, rasping, tongue-like organ Ribbon-like membrane has rows of tiny teeth (up to 250,000) pointed backward Ribbon-like membrane has rows of tiny teeth (up to 250,000) pointed backward Radula rasps off particles of food from surfaces Radula rasps off particles of food from surfaces Serves as a conveyor belt to move particles to digestive tract Serves as a conveyor belt to move particles to digestive tract New rows of teeth replace those that wear away New rows of teeth replace those that wear away Pattern and number of teeth are used in classification of molluscs Pattern and number of teeth are used in classification of molluscs Some specialized to bore through hard material or harpoon prey Some specialized to bore through hard material or harpoon prey Form and Function

12. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 16-12 Radula

13. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Foot Foot Functions in attachment or locomotion Functions in attachment or locomotion Modifications include Modifications include Hatchet foot of clams Hatchet foot of clams Siphon jet of squids Siphon jet of squids Secreted mucus aids in adhesion or helps molluscs glide Secreted mucus aids in adhesion or helps molluscs glide Snails and bivalves extend the foot by engorgement with blood Snails and bivalves extend the foot by engorgement with blood Form and Function

14. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 16-14 Shell Shell If present, secreted by the mantle If present, secreted by the mantle Periostracum Periostracum Outer layer - wears away Outer layer - wears away Composed of hardened protein Composed of hardened protein Middle prismatic layer Middle prismatic layer Closely packed prisms of calcium carbonate Closely packed prisms of calcium carbonate Increases with animal growth Increases with animal growth Inner nacreous layer Inner nacreous layer Next to the mantle; the nacre is laid down in thin layers Next to the mantle; the nacre is laid down in thin layers Aids in Pearl formation Aids in Pearl formation Shiny layer in abalone, nautilus, and bivalve Shiny layer in abalone, nautilus, and bivalve Form and Function

15. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 16-15 A.Bivalve Shell B. Pearl Formation from a parasite or sand that enters shell into mantle, becomes covered with nacre

16. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 16-16 Reproduction and Life History Reproduction and Life History Most dioecious, some hermaphroditic Most dioecious, some hermaphroditic Egg hatches and produces a free- swimming trochophore larva Egg hatches and produces a free- swimming trochophore larva In many gastropods and bivalves In many gastropods and bivalves Trochophore is followed by intermediate larval stage, the veliger. Trochophore is followed by intermediate larval stage, the veliger. Form and Function

17. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 16-17 Trochophore larva

18. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Classes of Molluscs Class Polyplacophora - Chitons Class Gastropoda - Slugs, Snails, Nudibranch Class Bivalvia - Clams, Mussels Class Cephalopoda - Squid, Octopus, Nautilus

19. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 16-19 Class Polyplacophora: Chitons Chitons are somewhat flattened with 7or 8 dorsal plates Chitons are somewhat flattened with 7or 8 dorsal plates Most prefer rocky intertidal surfaces Most prefer rocky intertidal surfaces Chiton radula is reinforced with iron mineral Chiton radula is reinforced with iron mineral Scrapes algae from the rocks Scrapes algae from the rocks Classes of Molluscs

20. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 16-20 Mossy Chiton - hairs and bristles aid in defense

21. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 16-21 Class Gastropoda Most diverse class Most diverse class Over 70,000 living Over 70,000 living Forms range from marine forms to air- breathing terrestrial snails and slugs Forms range from marine forms to air- breathing terrestrial snails and slugs Shells, if present, are chief defense Shells, if present, are chief defense Some produce distasteful or toxic secretions Some produce distasteful or toxic secretions Use process of Torsion Use process of Torsion Classes of Molluscs

22. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 16-22 Gastropod Shells Gastropod Shells One-piece (univalve) One-piece (univalve) Apex is smallest and oldest whorl Apex is smallest and oldest whorl Whorls become larger and spiral around central axis Whorls become larger and spiral around central axis Giant marine gastropods have shell up to 60 cm long Giant marine gastropods have shell up to 60 cm long Some fossil forms are 2 meters long Some fossil forms are 2 meters long Terrestrial gastropods shells are restricted by soil mineral content, temperature, dryness, and acidity Terrestrial gastropods shells are restricted by soil mineral content, temperature, dryness, and acidity Classes of Molluscs

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24. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 16-24 Form and Function Form and Function Torsion Torsion Developmental process that changes the relative position of the shell, digestive tract and anus Developmental process that changes the relative position of the shell, digestive tract and anus Digestive tract moves so that anus lies above head Digestive tract moves so that anus lies above head Classes of Molluscs

25. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 16-25 Coiling Coiling Coiling or spiral winding Coiling or spiral winding of the shell and visceral mass not the same as torsion Classes of Molluscs

26. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 16-26 Abalone - Feed on kelp -herbivore Moon Snail - feeds on clams and mussels Radula releases chemicals to soften shell, so they can get to their prey

27. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 16-27 Conus - Extends proboscis to capture prey. Then releases Conotoxins to paralyze (lethal to Humans) Hours later regurgitate scales and bones

28. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 16-28 Internal Form and Function Internal Form and Function Respiration performed by vascular area in mantle cavity that serves as lung Respiration performed by vascular area in mantle cavity that serves as lung Most have a single nephridium (kidney) and well- developed open-circulatory and nervous systems Most have a single nephridium (kidney) and well- developed open-circulatory and nervous systems Sense organs include eyes, statocysts, tactile organs, and chemoreceptors Sense organs include eyes, statocysts, tactile organs, and chemoreceptors Eyes vary from simple cups holding photoreceptors to a complex eye with a lens and cornea. (On tentacle of some) Eyes vary from simple cups holding photoreceptors to a complex eye with a lens and cornea. (On tentacle of some) Classes of Molluscs

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30. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 16-30 Reproduction: Reproduction: Eggs emitted singly or in clusters, and may be transparent or in tough egg capsules Eggs emitted singly or in clusters, and may be transparent or in tough egg capsules Young may emerge as veliger larvae or pass this stage inside the egg Young may emerge as veliger larvae or pass this stage inside the egg Some species, including most freshwater snails, are ovoviviparous Some species, including most freshwater snails, are ovoviviparous Classes of Molluscs

31. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 16-31 Eggs - resemble grains of wheat Egg ribbon of Nudibranch Eggs of Mollusks

32. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 16-32 Major Groups of Gastropods Major Groups of Gastropods Traditional classification has recognized three subclasses of Gastropoda Traditional classification has recognized three subclasses of Gastropoda Prosobranchia, Prosobranchia, Opisthobranchia Opisthobranchia Pulmonata Pulmonata Classes of Molluscs

33. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 16-33 Diodora aspera Hole in Apex for water to leave Gastropods - Prosobranchia Includes most marine snails Includes most marine snails Have one pair of tentacles, separate sexes Have one pair of tentacles, separate sexes Flamingo Tongue Snails

34. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 16-34 Sea Hare Sea Hare’s defense mechanism- a secretion from its purple gland sea slugs, sea hares, sea butterflies, and nudibranch Opisthobranches: sea slugs, sea hares, sea butterflies, and nudibranch Marine, Shell is reduced or absent 2 tentacles,

35. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 16-35 Nudibranch - calcareous spicules for protection

36. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 16-36 Pulmonates - Snail and Banana slug 2 tentacles: posterior have eyes Opening to Mantle Cavity

37. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 16-37 Class Bivalvia Mussels, clams, scallops, oysters Mussels, clams, scallops, oysters Range in size from 1–2 mm in length to the giant South Pacific clams (1m) Range in size from 1–2 mm in length to the giant South Pacific clams (1m) Most are sedentary filter feeders Most are sedentary filter feeders Bivalves lack a head, radula, or other aspects of cephalization Bivalves lack a head, radula, or other aspects of cephalization Contain Siphons Contain Siphons Classes of Molluscs

38. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 16-38 Mussels Scallops Escaping a Sea Star

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40. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 16-40 Northwest Ugly Clams Siphons Incurrent brings in Food and Oxygen

41. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 16-41 Form and Function Form and Function 2 shells or valves are held together by a hinge ligament 2 shells or valves are held together by a hinge ligament Valves are drawn together by strong adductor muscles Valves are drawn together by strong adductor muscles Umbo is the oldest part of the shell with growth occurring outward in rings Umbo is the oldest part of the shell with growth occurring outward in rings Posterior edges of the mantle folds form excurrent and incurrent openings Posterior edges of the mantle folds form excurrent and incurrent openings In burrowing clams, mantle forms long siphons to reach the water above In burrowing clams, mantle forms long siphons to reach the water above Classes of Molluscs

42. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 16-42 Locomotion Locomotion Foot is extended out from between the valves Foot is extended out from between the valves Blood is pumped into the foot Blood is pumped into the foot Foot swells and anchors the bivalve in the mud Foot swells and anchors the bivalve in the mud Shortening of the foot pulls the clam forward Shortening of the foot pulls the clam forward Scallops clap valves to create a jet propulsion Scallops clap valves to create a jet propulsion Classes of Molluscs

43. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 16-43 Scallop - developed sensory organs along mantle edges (tentacles and blue eyes)

44. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 16-44 Gills Gills Both mantle and gills perform gaseous exchange Both mantle and gills perform gaseous exchange Siphon used in respiratory Siphon used in respiratory Water enters incurrent siphon Water enters incurrent siphon Gas diffused out Gas diffused out Exits through the excurrent siphon Exits through the excurrent siphon Circulatory - Open circulatory system Circulatory - Open circulatory system 3 chambered heart has two atria and one ventricle 3 chambered heart has two atria and one ventricle Blood vessels line gills to receive oxygen Blood vessels line gills to receive oxygen Classes of Molluscs

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46. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 16-46

47. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 16-47 Shipworm Bivalves- Burrows into wood on docks and piers

48. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 16-48 Clam - Symbiotic relationship with Algae to gain most nutrients Siphonal Area

49. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 16-49 Reproduction and Development Reproduction and Development Sexes usually separate Sexes usually separate Gametes discharged in excurrent flow Gametes discharged in excurrent flow Fertilization usually external Fertilization usually external Embryos develop as trochophore, and veliger larval stages Embryos develop as trochophore, and veliger larval stages Freshwater clams have internal fertilization Freshwater clams have internal fertilization Sperm enter the incurrent siphon to fertilize eggs in water tubes of the gills Sperm enter the incurrent siphon to fertilize eggs in water tubes of the gills Larvae develop into a bivalved glochidia stage Larvae develop into a bivalved glochidia stage Attaches to gills of passing fish where they live briefly as parasites Attaches to gills of passing fish where they live briefly as parasites “Hitchhiking” having helped distribute the species “Hitchhiking” having helped distribute the species Classes of Molluscs

50. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 16-50 Life Cycle of an Oyster

51. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 16-51 Glochidium - freshwater clam larva Attach to fish’s gills by clamping their valve closed. Stay for several weeks. Pocketbook Mussel - mimics a small minnow, when a Smallmouth Bass comes to dine, it releases its glochidia

52. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 16-52 Class Cephalopoda Squids, octopuses, nautiluses, and cuttlefish Squids, octopuses, nautiluses, and cuttlefish All marine predators All marine predators Foot is in the head region Foot is in the head region Modified for expelling water from mantle cavity Modified for expelling water from mantle cavity Range from 2 cm to the giant squid (60 ft) Range from 2 cm to the giant squid (60 ft) Largest invertebrate Largest invertebrate Nautilus - only one with external shell Nautilus - only one with external shell Series of gas chambers in shell helps maintain neutral buoyancy Series of gas chambers in shell helps maintain neutral buoyancy Classes of Molluscs

53. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 16-53 Nautilus A. Feed on a Fish B. Showing Gas filled chambers

54. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 16-54 Cuttlefish

55. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 16-55 Locomotion Locomotion Cephalopods swim by forcefully expelling water through a ventral funnel or siphon Cephalopods swim by forcefully expelling water through a ventral funnel or siphon Control direction and force of the water, thus determining its speed Control direction and force of the water, thus determining its speed Lateral fins of squids and cuttlefishes are stabilizers Lateral fins of squids and cuttlefishes are stabilizers Nautilus swims mainly at night Nautilus swims mainly at night Octopuses mainly crawl on the bottom but can swim Octopuses mainly crawl on the bottom but can swim Some with webbing between their arms swim with a medusa-like action Some with webbing between their arms swim with a medusa-like action Classes of Molluscs

56. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 16-56 Squid - Pen is only remains of shell

57. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 16-57 Respiration and Circulation Respiration and Circulation With higher oxygen demands, cephalopods have a muscular pumping system to keep water flowing through the mantle cavity With higher oxygen demands, cephalopods have a muscular pumping system to keep water flowing through the mantle cavity Circulatory system has a network of vessels conducting blood through gill filaments (Closed Circulatory System!!) Circulatory system has a network of vessels conducting blood through gill filaments (Closed Circulatory System!!) Classes of Molluscs

58. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 16-58 Nervous and Sensory Systems Nervous and Sensory Systems Cephalopod brain is the largest of any invertebrate Cephalopod brain is the largest of any invertebrate Squids have giant nerve fibers Squids have giant nerve fibers Sense organs are well-developed Sense organs are well-developed Eyes are complex, complete with cornea, lens, and retina Eyes are complex, complete with cornea, lens, and retina Can learn by reward and punishment, and by observation of others Can learn by reward and punishment, and by observation of others Cephalopods lack a sense of hearing but have tactile and chemoreceptor cells in their arms Cephalopods lack a sense of hearing but have tactile and chemoreceptor cells in their arms Classes of Molluscs

59. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 16-59 Cuttlefish Eye

60. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 16-60 Communication Communication Use chemical and visual signals to communicate Use chemical and visual signals to communicate Chromatophores are cells in the skin that contain pigment granules Chromatophores are cells in the skin that contain pigment granules Contractions of the muscle fibers attached to the cell causes the cell to expand and change the color pattern Contractions of the muscle fibers attached to the cell causes the cell to expand and change the color pattern Color patterns can be changed rapidly Color patterns can be changed rapidly Deep-water cephalopods have elaborate luminescent organs Deep-water cephalopods have elaborate luminescent organs Ink sac empties into rectum; (Not in Nautiloids) Ink sac empties into rectum; (Not in Nautiloids) Contains ink gland that secretes sepia (dark fluid) when animal is alarmed Contains ink gland that secretes sepia (dark fluid) when animal is alarmed Classes of Molluscs

61. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 16-61 Reproduction Reproduction Sexes are separate Sexes are separate In male seminal vesicle, spermatozoa are packaged in spermatophores and stored In male seminal vesicle, spermatozoa are packaged in spermatophores and stored One arm of male is modified as an intromittent organ, the hectocotylus One arm of male is modified as an intromittent organ, the hectocotylus Removes a spermatophore from mantle cavity and inserts it into female Removes a spermatophore from mantle cavity and inserts it into female Fertilized eggs leave oviduct and are attached to stones, etc. Fertilized eggs leave oviduct and are attached to stones, etc. Large, yolky eggs undergo meroblastic cleavage (not full cleavage) Large, yolky eggs undergo meroblastic cleavage (not full cleavage) Hatch into juveniles with no free-swimming larval stage Hatch into juveniles with no free-swimming larval stage Classes of Molluscs

62. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 16-62 Copulation in Cephalopods - Male Octopus uses modified arm