Mollusca

1413 Presentation

1. Mollusca

2. Phylum Mollusca Diversity - 90,000 species (Hickman et al. 2017) 8 classes: Caudofoveata, Solenogastres, Polyplacophora, Monoplacophora, Gastropoda, Bivalvia, Scaphopoda, Cephalopoda

3. Phylum Mollusca

4. Phylum Mollusca

5. Phylum Mollusca

6. Phylum Mollusca

7. General Characteristics Most versatile body plan of all animals Divided into 8 classes Most diversity is in two (Gastropoda and Bivalvia) Microscopic to 20m in length Most are less than 10 cm Sessil to fast swimmers Occupy marine, fresh, and terrestrial biospheres Only Gastropoda and Bivalvia in freshwater Only gastropoda in terrestrial areas Must be moist and with calcium in soil

8. General Characteristics Form and Function Despite wide variety of body plans, some basic features shared Mantle - secretes shell (or becomes outer body covering) Visceral mass - most internal organs (embedded in tissue) Shell - external or internal Radula - specialized feeding organ Foot - used for locomotion

9. General Characteristics Body in two parts Head-foot Visceral mass

10. General Characteristics Body in two parts Head-foot More active region of a mollusc Contains feeding, sensory, and locomotor organs Radula - tongue-like rasping organ Present in all except bivalves and solenogastres File-like, may have 250,000 teeth New teeth continually produced Supported on cartilage-like rod - odontophore Works like a conveyor belt to deliver food to digestive tract

11. General Characteristics Radula

12. General Characteristics Radula

13. General Characteristics Body in two parts Head-foot Foot is present in all molluscs (used for locomotion) Creeping movements Slime trail Digging Attachment Byssal threads For some, modified into proboscis

14. General Characteristics Body in two parts Head-foot Foot is present in all molluscs (used for locomotion) Creeping movements Slime trail Digging Attachment Byssal threads For some, modified into proboscis

15. General Characteristics Body in two parts Head-foot Foot is present in all molluscs (used for locomotion) Creeping movements Slime trail Digging Attachment Byssal threads For some, modified into proboscis

16. General Characteristics Body in two parts Head-foot Foot is present in all molluscs (used for locomotion) Creeping movements Slime trail Digging Attachment Byssal threads For some, modified into proboscis

17. General Characteristics Body in two parts Head-foot Foot is present in all molluscs (used for locomotion) Creeping movements Slime trail Digging Attachment Byssal threads For some, modified into proboscis

18. General Characteristics Body in two parts Visceral mass - contains digestive, respiratory, and reproductive organs Depends primarily on ciliary tracts for functioning Mantle - body wall of molluscs. Made of epidermis May have sense organs and glands Glands secrete mucus, cement, and shell (some) Mantle may create mantel cavity Cavity houses respiratory organs For some, mantle cavity may offer protection

19. General Characteristics Mantle and mantle cavity

20. General Characteristics Mantle and mantle cavity

21. General Characteristics Mantle and mantle cavity

22. General Characteristics Body in two parts Visceral mass - contains digestive, respiratory, and reproductive organs Shell - secreted by mantle Much variability in form and structure Made of calcium carbonate 3 layers Periostracum Outer, thick in freshwater; thin or absent in marine Prismatic Middle, very dense Nacreous Inner, glossy and secreted throughout life

23. General Characteristics

24. Homeostatic Structures and Functions Respiration Most molluscs have folded, ciliated gills (ctenidia) Used for feeding in bivalves Bivalves may have extended siphon Some molluscs respire through skin Many terrestrial snail lack gills (pulmonates) Mantle is modified into saclike lung for breathing air Pneumostome present

25. Homeostatic Structures and Functions Respiration

26. Homeostatic Structures and Functions Respiration

27. Homeostatic Structures and Functions Respiration

28. Homeostatic Structures and Functions Circulation Most have an open circulatory system Blood is not entirely contained within vessels Adequate for slow moving animals Cephalopods have closed circulation Heart is simple and has few vessels 2 auricles and 1 ventricle Coelom is reduced and becomes haemocoel surrounding heart Blood has both oxygen carrying cells and white blood cells No thrombocytes Haemocyanin (Cu) - most, blue in color Hemoglobin (Fe) - fewer, red in color

29. Homeostatic Structures and Functions Circulation

30. Homeostatic Structures and Functions Circulation

31. Homeostatic Structures and Functions Feeding and Digestion Detritus feeders, burrowers, borers, grazers, carnivores, filter feeders, etc. Radula aids in feeding Most digestive organs are embedded in visceral mass Complete digestive system Foregut Midgut Hindgut

32. Homeostatic Structures and Functions Feeding and Digestion Foregut - receives and prepares food Buccal cavity Mouth Radula Salivary glands Esophagus

33. Homeostatic Structures and Functions Feeding and Digestion Midgut - storing region, crushing region Stomach Digestive glands Crystalline style Grinds food in some

34. Homeostatic Structures and Functions Feeding and Digestion Crystalline style

35. Homeostatic Structures and Functions Feeding and Digestion Hindgut - absorption of nutrients, formation of feces Intestine

36. Homeostatic Structures and Functions Excretion 1 pair of metanephridia Term kidney is used, but different from vertebrate kidney) Some excretion through body walls and gills

37. Nervous System Central nervous system - ring of ganglia in head area Paired ganglia extend to other parts of the body Nervous system is simple compared to vertebrates Cephalopods rival some mammals in reasoning and learning

38. Reproduction and development Most are dioecious Many gastropods (snails and slugs) are monoecious Marine formes produce larval stage known as trochophore For some, a secondary larval form (veliger) will form Cephalopods have direct development

39. Class Polyplacophora Where found Generally on rocky surfaces in intertidal regions Move very little over lifetime Clings to rocks with broad foot Capable of rolling up like armadillo or pangolin for protection At low tide, can press margin of mantle against substrate Lessens water loss

40. Class Polyplacophora General morphology Small, 2-5 cm Dorsoventrally flattened Convex dorsal surface 7 to 8 plates on dorsal side (mantle may cover) Generally dull in color Head reduced Mantle cavity extended along sides of foot

41. Class Polyplacophora Feeding Complete digestive tract Use radula to scrape algae Magnetite in radula makes stronger One predaceous species

42. Class Polyplacophora Reproduction Sexes are separate in most Larva produced as trochophore No veliger stage

43. Class Gastropoda General characters Largest and most diverse class of molluscs Variety of body forms and names Snails, limpets, slugs, whelks, conchs, periwinkles, sea slugs, sea hares, sea butterflies. Generally slow moving or sedentary with heavy shells

44. Class Gastropoda General characters Shells Always univalve (single piece) May be coiled or uncoiled Top is apex and contains the oldest and smallest whorl Whorls become larger as they spiral down the columella (central axis) Open is aperture and may be covered by an operculum

45. Class Gastropoda General characters Shells Always univalve (single piece) May be coiled or uncoiled Top is apex and contains the oldest and smallest whorl Whorls become larger as they spiral down the columella (central axis) Open is aperture and may be covered by an operculum

46. Class Gastropoda General characters Shells Dextral or sinistral Right or left handed coiling Genetically controlled and right predominates

47. Class Gastropoda Torsion Process whereby the anus, shell, and mantle cavity containing the gills moves from the posterior to anterior Occurs during development, but may not remain into adulthood (detorsion)

48. Class Gastropoda Torsion Consequences Torsion prevents growth in length; gastropod must grow upward into shell Anus now over mouth Fouling What favored torsion? Most likely the advantage of withdrawing the head into the mantle cavity Provides protection

49. Class Gastropoda Coiling Ancestral gastropods has a planispiral (planospiral) shell All whorles stacked on top of one another. Bulky arrangement; snail became much taller as it grew Solution was coiling

50. Class Gastropoda Feeding habits Varied, but all utilize the radula in some fashion Herbivores - algae scrapers, grazers, browsers

51. Class Gastropoda Feeding habits Varied, but all utilize the radula in some fashion Herbivores - algae scrapers, grazers, browsers Borers - bore into other mollusc shells

52. Class Gastropoda Feeding habits Varied, but all utilize the radula in some fashion Herbivores - algae scrapers, grazers, browsers Borers - bore into other mollusc shells Predators - use radula to help capture food

53. Class Gastropoda Feeding habits Varied, but all utilize the radula in some fashion Herbivores - algae scrapers, grazers, browsers Borers - bore into other mollusc shells Predators - use radula to help capture food Conus - conotoxin

54. Class Gastropoda Internal form and function Respiration Mostly by ctenidium (two gills) located inside mantle cavity Pulmonates lack gills, but have highly vascularized region Pneumostome

55. Class Gastropoda Internal form and function Excretion - single nephridium (kidney) Circulatory - open Nervous - well developed Three pairs of ganglia Photoreceptors, statocysts, tactile organs, chemoreceptors

56. Class Gastropoda Major groups of gastropods Prosobranchs - marine snails and some freshwater and terrestrial groups Opisthobranchs - sea slugs, sea hares, sea butterflies, bubble shells Nearly all marine Pulmonates - land snails and freshwater snails Ctenidia lost

57. Class Bivalvia General characters Most will feed by creating ciliary currents that draw water and suspended food particles over gills (filter feeding) Lack head, radula, and cephalization (concentration of sensory structures)

58. Class Bivalvia General characters Shells always in two parts Hinge ligament at dorsal side Drawn together by adductor muscles Umbo is oldest part of shell

59. Class Bivalvia Body and Mantle Visceral mass suspended from dorsal midline Muscular foot attached to visceral mass Ctenidia (gills) hang on either side of visceral mass and foot Mantle covers gills Gills lie in mantle cavity Shell to mantle to gill to visceral mass to gill to mantle to shell Mantle may be extended into long siphons Always forms some siphon (excurrent and incurrent)

60. Class Bivalvia Locomotion Most initiate movement by extending the foot through the gap of the valves Blood is then pumped into the foot causing it to swell Acts as anchor Longitudinal muscles shorten the foot and pull the animal forward.

61. Class Bivalvia Locomotion Most initiate movement by extending the foot through the gap of the valves Scallops move by jet propulsion Rapidly open and close valves to create a jet of water

62. Class Bivalvia Gills Gas exchange occurs over both gills and mantle Gills appear as elongated “Ws” Form lamellae Water drawn in through incurrent siphon Passes through pores into tubes and then to suprabranchial chamber and out excurrent siphon

63. Class Bivalvia Gills Gas exchange occurs over both gills and mantle Gills appear as elongated “Ws” Form lamellae Water drawn in through incurrent siphon Passes through pores into tubes and then to suprabranchial chamber and out excurrent siphon

64. Class Bivalvia Feeding Most are filter feeders As water is drawn in, mucus is secreted Entangles food particles Mucus and food slide down gillsto food groove at base of gills Mucus and food travel along the groove towards labial palps Palps direct food into mouth

65. Class Bivalvia Feeding

66. Class Bivalvia Feeding Floor of stomach is folded into ciliary tracts for sorting food particles In most, a styl sace secretes the crystalline style Constantly rotting Dissolves its surface layer and rolls the mucus mass Dislodged food particles are sorted by the base of the stomach Large particles to intestine Small to digestive gland

67. Class Bivalvia Feeding

68. Class Bivalvia Circulation Three-chambered heart with open circulation Excretion Pair of U-shaped kidneys (nephridial tubes) Empty into suprabranchial chamber Nervous system Three pairs of ganglia; poorly developed sense organs Scallops have eyes

69. Class Bivalvia Reproduction Sexes usually separate For many, fertilization is external and gametes are shed into water Freshwater forms have internal fertilizations Many produce glochidia larvae Live parasitically on gills of fish Some discharge glochidia into water Others attract fish and cast glochidia directly at fish gills

70. Class Bivalvia Reproduction

71. Class Cephalopoda Squids, octopuses, nautiluses, devilfish, cuttlefish, and extinct ammonites All are marine; all are active predators

72. Class Cephalopoda General characters Foot is merged with head Forms funnel for expelling water and a crown of tentacles May be small (2-3 cm) or large (19 m) Ancestrally, shell was present and straight Derived forms have curved, coiled, reduced, or absent shell Found at great depths and shallow intertidal zones

73. Class Cephalopoda Shell Coiled in Nautiloids and extinct ammonoids Although heavy, made buoyant by gas-filled chambers Chambers walled-off from one another and only last is inhabited Cord of living tissue, siphuncle, connects through all chambers

74. Class Cephalopoda Shell Internal and curved in cuttlefish Squids reduced to the pen Absent in octopuses

75. Class Cephalopoda Locomotion Squids and cuttlefish are excellent, fast swimmers Nautiloids are much slower Octopuses are capable of rapid, backward movement, but are better built for crawling among rocks

76. Class Cephalopoda Respiration All cephalopods (except nautiloids) have one set of gills Gills lack cilia Rather, water is drawn over by changes to the shape of the mantle cavity Circulation Circulatory system is closed Systemic heart served body Branchial hearts increase blood pressure at gills

77. Class Cephalopoda Nervous system More elaborate than other molluscs Largest brain of any invertebrate Senses are well developed Eyes are single-lens, large, and complex No color vision; but superb underwater resolution

78. Class Cephalopoda Communication Through chromatophores Cells will pigments Cell shape can be changed, thus the amount of pigment shown can also be changed Allows for rapid change in appearance

79. Class Cephalopoda Reproduction Sexes are separate Spermatozoa encased in spermatophores Males with specializes tentacles to retrieve spermatophore and pass it to female Development is direct