1. Phylum Mollusca

4. All have bilateral symmetry (at least as juveniles) All are coelomate (alternative term: eucoelomate) All have a complete digestive tract (mouth and anus) Mollusks, Annelids, and Arthropods Mollusks, Annelids, and Arthropods

6. unsegmented muscular foot (may be highly modified) mantle – membrane present in all; in most, secretes and maintains one or two calcerous valves (shells) most have a radula (rasping tongue with chitinous teeth) Mollusks (Phylum Mollusca)

7. Diverse group, over 100,000 living species (2 nd ranking in number among animal phyla) Of 7 classes, 4 classes covered: Polyplacophora (chitons) Gastropoda (gastropods) – snails, slugs, and nudibranchs (sea slugs) Bivalvia (bivalves) – scallops, oysters, clams, etc. Cephalopoda (cephalopods) – octopi, squid, cuttlefish, etc. Mollusks (Phylum Mollusca)

8. Symmetry of the Mollusk Most mollusks are bilaterally symmetrical

9. A Closer look at Mollusca The foot - a broad, flat muscular organ that is adapted for locomotion and attachment The visceral mass - contains the internal organs The mantle - a fold of tissue that drapes over the visceral mass; space between the mantle and the visceral mass is called the mantle cavity

10. Mollusks – Body plan Usually divided into two parts 1. Head-foot 2. Visceral mass Head-foot contains –Head – contains mouth –Sensory structures –Foot - large muscle used for movement Visceral mass contains –Heart –Digestive organs –Excretion organs –Reproduction organs

11. The Mantle of the Mollusk Mantle –covering of the visceral mass that secretes the shell –Positives! Protection –Negatives! Reduce surface area for gas exchange Solved by having gills for gas exchange

12. The Shell The mantle is responsible for secreting the shell. The shell is comprised of three layers: The outside of the shell is covered by an organic layer - periostracum The middle prismatic layer is characterized by densely packed prisms of calcium carbonate laid down in a protein matrix The inner nacreous layer is composed of calcium carbonate sheets laid down over a thin layer of protein

13. Nervous Tissue of the Mollusk Ganglia – –Cluster of nerve cells used for… Feeding Locomotion Sensory information –Some are incredibly intelligent, more on this later!

14. The gills of the mollusca are often indicated as one or more pairs of bipectinate gills, - flattened filaments attached to a longitudinal axis on either side Gills

15. Digestive System of the Mollusk Radula –tongue like tissue covered with sharp teeth for scraping food Complete Digestive System –Some mollusks filter feed, while others are predators

16. The Radula The mouth cavity of mollusca possesses a specialized rasping organ called the radula; sits on a cartilaginous structure - odontophore Particles of food brought into the mouth are bound in mucous secreted by the salivary glands

17. Circulation of the Mollusk Most mollusks, (except cephalopods), have an open circulatory system –Hemolymph is the fluid that is contracted into sinuses and “washes” over body organs for nutrient and gas exchange. –In other words, unlike a closed circulatory system, the blood is not kept in capillaries, veins, and arteries while it moves throughout the body

19. Reproduction of the Mollusk All Mollusks reproduce sexxually –Depending on the species of mollusk, some reproduce externally or internally –Dioecious- Have male and female –Some are hermaphroditic

20. Molluscan Larval Stages Most molluscs produce a free- swimming ciliated larvae called the trochophore larvae In some molluscs the trochophore develops into the adult, but in other molluscs (e.g., gastropods) there is a second larval stage called the veliger

21. Mollusk Larvae Trocophore Larvae –Free-swimming larval stage (first form) Veliger larvae –Free-swimming larval stage with foot, eyes, tentacles, and shell

22. Class Polyplacophora Chitons! –Many-plated mollusk –Lives in shallow marine water –Feed on algae attached to rock

23. Polyplacophora – chiton (display only): eight overlapping valves muscular foot thick mantle gills Mollusks (Phylum Mollusca)

24. Class Polyplacophora (Chitons) Common on the rocky surfaces of the intertidal zone Head is poorly developed; ventral surface occupied by a broad, flattened foot Has a dorsal shell composed of 8 overlapping plates, arranged linearly along the anterior-posterior axis Within the grooves lie many bipectinate gills

26. Class Gastropoda Single external shell Radula for scraping food Moves in wave like contractions through slime Can be hermaphrodites, though commonly not Ex) Snails, slugs

27. Class Gastropoda Snails live on land or in fresh or salt water –They have eyes on tentacles on their head Slugs live on land and Sea Slugs (a.k.a. nudibranches) live in the ocean –Slugs do not have shells –Have exchange of oxygen (diffusion) across their entire body

28. Gastropoda More active than mono and polyplacophorans –Highly cephalized: tentacles, eyes Gonochoristic Veliger larva (an advanced version of the trochophore larva)

29. Class Gastropoda Three evolutionary innovations occurred among the gastropods: changes in the shell, increased development of the head, the embryonic process of torsion 1. Changes in the Shell The shell became higher and conical with a reduced aperture The shell also became coiled Shells initially were planospiral - bilaterally symmetrical shell with the whorls lying in the same plane Modern day shells are asymmetrical - each successive coil is a little outside and offset a little above the one below

30. Torsion is unique to gastropods Most gastropods are dextral Pretorsion Post torsion

31. 3. The Embryonic Process known as Torsion During embryonic development, 1 side of the visceral mass grows at a much faster rate than the other. Causes the visceral mass to rotate 180 degrees relative to the head- foot. Advantages: head retracted first; gills receive water currents; the osphradium is now directed anteriorly Disadvantage: may cause fouling

32. Adaptations to Avoid Fouling Improved separation of inhalent and exhalent water flow In some of the more primitive gastropods (keyhole limpets), the shell contains a hole at the top through which the exhalent water stream exits In the more advanced gastropods, water is brought into the mantle cavity on the left side, passes over a single gill, and exits the right side

33. Shell Most have a single, spiraled shell and can move the entire head and foot into this shell for protection. Also, many gastropods have a hardened plate called the operculum on the back of the foot that plugs the shell aperture when the body is withdrawn

34. Nutrition Many gastropods are herbivores and use their radula scrap algae from surfaces of rocks Some gastropods are active predators and in these the radula is often highly modified, e.g., as a drill (oyster drills) or harpoon (venomous gastropods) Cone snail

35. Respiration Aquatic gastropods possess gills for respiration Terrestrial gastropods obtain oxygen via a well vascularized mantle gills Vascularized mantle

36. Pulmonata Highly vascularized mantle for gas exchange (lung) 17,000 spp: slugs, pond snails

37. Snail infestations!

38. Sea Slugs!

40. Bivalvia – clam: two valves, connected by dorsal hinge ligament adductor muscles (used by living clam to close the shell) gills in mantle cavity wedgelike foot Mollusks (Phylum Mollusca)

41. Bivalves Sessile Filter-feeders Extend the muscular foot into the sand to anchor it No specific head – but has ganglia

42. Class Bivalvia – Two Shells Three layers make up the shell of a bivalve –Inner most protects the body of the animal –Middle layer strengthens the shell with calcium carbonate –Outer layer protects against acid in the water

43. Pallial muscles insert on the underside of the shell and are attached to the free edge of the mantle; pull the mantle under the shell Muscles fused across the width (from left to right) at 1 anterior and posterior position and form adductor muscles; connect the 2 shell across their width; close the shell When relaxed, shell swings open due to elastic ligaments of the hinge

44. Class Bivalvia Shells divided into 2 equal halves or valves Mantle tissue is indented in the anterior- posterior margins, with 2 centers of calcification Shells joined at the dorsal midline by a non calcified protein ligaments called the hinge

45. Bivalves No radula sexual reproduction Incurrent and excurrent siphons –Help filter water in and out of the clam

46. Movement of the Ventilating Currents

47. Adaptive Radiation of Bivalves con’t Unattached Surface Dwellers Rest unattached on the substrate Capable of limited locomotion by rapid clapping of their valves using a powerful adductor muscle; forces a jet of water out of the mantle cavity Hard Bottom Burrowers Several species of bivalves are capable of burrowing into hard surfaces such as rock, coral, wood Use the anterior margins of their shell to chip away at the rock; some secrete chemical to breakdown rock

48. Adaptive Radiation of Bivalves

49. Reproduction Most are dioecious Marine forms usually produce free swimming trochophore and veliger larvae Many of the freshwater bivalves have a different life history pattern; produce larvae called glochidia Glochidia are housed in the outer gills; they use there outer gill as a brood camber - marsupium When the glochidia are released they parasitize the fins and gills of fishes

50. : Cephalopoda – squid: muscular foot with tentacles (with suction discs) thick mantle but no external shell (true for most cephalopods) excurrent siphon (for jet propulsion) large eyes Mollusks (Phylum Mollusca)

51. Class Cephalopoda Means “head foot” Includes octopuses, squids, cuttlefishes and chambered nautiluses Free swimming and predatory Tentacles with suction cups to grasp prey Have jaws called beaks to destroy their prey Has the largest invertebrate brain

52. Cephalopods Can learn to perform tasks Has complex eyes Closed circulatory system Are sexual - internal Have ink to confuse predators

53. Cephalopoda Swift, agile carnivores Closed circulatory system, 2 hearts Separate sexes Foot modified to form arms, tentacles, siphon Brain, cranium, complex image-forming eye 700 extant spp, 10,000 extinct spp Arose from limpet-like monoplacophorans Ergo, ventral became function anterior, etc

54. Cephalopods

55. Endocochleate cephalopds –Reduce internal shell, or shell absent –Squids, cuttlefish, octopi Cephalopoda

56. Class Cephalopoda Fast moving predators of the marine environment Cephalopods evolved following major readjustments in the mollusca body plan: Dorso-ventral axis became elongated and the anterior-posterior axis became compressed Migration of the head to the ventral part of the body where it fused to the foot The foot is modified as a series of prehensile tentacles or arms A circle of 8 or 10 tentacles surround the head; studded with suckers and are used to capture prey.

57. Class Cephalopoda Fast moving predators of the marine environment Cephalopods evolved following major readjustments in the mollusca body plan: Dorso-ventral axis became elongated and the anterior-posterior axis became compressed Migration of the head to the ventral part of the body where it fused to the foot The foot is modified as a series of prehensile tentacles or arms A circle of 8 or 10 tentacles surround the head; studded with suckers and are used to capture prey.

58. Locomotion Cephalopods are excellent swimmers: streamlined body; tentacles and fins as stabilizers Swim by means of jet propulsion, using the highly modified muscular mantle and the siphon –By relaxing the mantle the mantle cavity is expanded and water can be drawn in –By contracting the mantle water can be forced out of the mantle cavity by means of the small siphonal opening

59. Feeding Cephalopods are carnivores Have a powerful parrot like beak that is used to tear prey apart. They also have a powerful radula In some of the octopuses the salivary glands are modified poison glands

60. Shell Primitively the cephalopods possessed a shell; the fossil record indicates both coiled and non-coiled shells Extant members with coiled shells include Nautilus Some cephalopods (cuttlefishes) have an internal shell - cuddle bone The octopods have lost the shell entirely

61. Other General Features For protection, they possess an ink sacs Cephalopods have well-developed sense organs, including a camera type eye Some have well-developed brains and show a remarkable capacity for learning. Cephalopods are the only molluscan class with a closed circulatory system

66. CephalopodaCephalopoda Dorsal Ventral Posterior surface Right Left

67. FinFin ArmArm Funnel (siphon) EyeEye TentacleTentacle CollarCollar

68. Shell (Pen) CtenidiumCtenidium FunnelFunnel SystemicheartSystemicheart Branchial heart Hectocotylus (sperm-bearing arm in males) Reproduction: trochophore and veliger are bypassed and hatch into planktonic juveniles

69. eye Optic lobe statocyst Cerebral ganglion Brain is surrounded by a cranium Brachial nerves Buccal ganglia esophagus

70. Cephalopod eye IrisIris LensLens CorneaCornea RetinaRetina Optic nerves

71. Squid and octopus: basic facts A standard squid has: Two fins A mantle A head 8 arms and two tentacles, each endowed with hooks and/or suckers and sucker rings A standard octopus has : A mantle A head 8 arms endowed with one or two rows of suckers (but never hooks or sucker rings); they have no tentacles

73. Giant optopus

74. Examples of Cephalopods A giant squid (3.15-metre-long) has netted off the UK coast; first time in 15 years. The squid, believed to be female and three years old, did not survive being brought to the surface. Close-up view of an unknown species of bathypelagic squid encountered by ROV Tiburon at 3,380 meters depth off the coast of Oahu. This animal was estimated to be four to five meters in length. Different from other squids in that their eight arms and two tentacles are roughly equal in length and thickness.

75. The Mimic Octopus

76. Cephalopoda Ectocochleate cephalopods –Have external shell with internally subdivisions used for buoyancy control –This ancestral group is almost completely extinct –E.g. Nautilus

78. Nautilus is the only cephalopod with an external shell and lacking chromatophores Chromatophores (color cells) Iridocytes (reflective cells) -Millions of these allow rapid changes in color, polarized signals -Also have photophores for bioluminescence Cephalopods except Nautilus have ink sac

79. Types of Cephalopods Squids have 10 tentacles Jet propulsion through excurrent siphon to move The colossal squid is the world’s largest invertebrate Octopuses have 8 tentacles Jet propulsion to capture prey but crawl along ocean floor

82. Blue-ringed Octopus -When threatened, faint blue rings become vivid to warn predators to back off -it’s one of the most deadly venomous animals -bites prey with its jaws -injects a venomous saliva into the wound - venom contains tetrodotoxin, one of the most potent neurotoxins known -Human death from heart & respiratory failure occurs within minutes. This non-aggressive octopus only bites people in self-defense.

83. Reflection: Mollusks are some of the most diverse phyla that we have seen so far. Reflect on how the differences in adaptations across the different classes can help the individual species in each class to survive!