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General Characteristics

General Characteristics. Contains 110,000 living species and 40,000 fossil species This phylum has all organ systems present Bilateral symmetry. General Characteristics. Ventral body wall modified into a muscular foot with various modifications but generally used for locomotion.

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General Characteristics

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  1. General Characteristics • Contains 110,000 living species and 40,000 fossil species • This phylum has all organ systems present • Bilateral symmetry

  2. General Characteristics • Ventral body wall modified into a muscular foot with various modifications but generally used for locomotion

  3. General Characteristics • Dorsal body wall forms the mantle which encloses the mantle cavity and is modified into the gills or lungs and also serves to secrete the shell (shell is absent in some species)

  4. General Characteristics • Eucoelomate body cavity – (have both peritoneal lining and mesentery) • Mollusca means soft-bodied • Reproduction is dioecious in some species and monoecious in some • Some molluscs are herbivorous grazers, some are carnivores and some are filter feeders or parasites • Most species are marine, but some are terrestrial or freshwater

  5. General Characteristics • This is a large phylum and includes the snails, slugs, chitons, nudibranchs, clams, mussels, oysters, squid, octopus and nautilus

  6. General Characteristics • Chiton

  7. General Characteristics • Nudibranch

  8. General Characteristics • Clam

  9. General Characteristics • Mussel

  10. General Characteristics • Oyster

  11. General Characteristics • Squid Saltwater Fly Squid

  12. General Characteristics • Octopus

  13. General Characteristics • Nautilus

  14. General Characteristics • This phylum is of some economic importance: • Many are used for food • Mother of Pearl buttons / jewelry are produced from shells of bivalves • Pearls both natural and cultured are produced from marine oysters • Shipworms are destructive, doing damage to wooden ships and wharves • Snails and Slugs can do great damage to gardens • Snails are intermediate hosts for many serious human parasites

  15. Form & Function • Mollusc body plan: head-foot and visceral mass • The head-foot provides for feeding, senses and locomotion

  16. Form & Function • The visceral mass contains digestive, circulatory, respiratory and reproductive organs

  17. Form & Function • Mantle Cavity: • Two folds of skin from the dorsal body wall form the mantle cavity • The mantle cavity holds the gills or lungs • In most molluscs, the mantle secretes a protective shell over the visceral mass for protection

  18. Form & Function • Head-Foot: most molluscs have a well-developed head region • Simple to complex eyes • Tentacles may be present • Posterior to mouth is the foot which is the organ of locomotion

  19. Form & Function • Radula is found in all molluscs except the bivalves, which are filter-feeders • The radula is a protruding rasping organ • Has tiny rows of teeth which point backward

  20. Form & Function • Radula rasps off fine particles of food from surfaces and then acts like a conveyor belt to move them backward to the digestive system

  21. Form & Function • Foot is usually ventral • Functions as an attachment organ or for locomotion • Free-swimming forms have modified the foot into wings or fins

  22. Form & Function • Shell: • When present, the shell is secreted by the mantle and lined by it • Made of three layers • Periostracum – outer horny layer made of tanned protein • Prismatic layer – middle layer made of Calcium Carbonate • Nacreous layer – inner lining made of thin layers of CaCo3formed continuously throughout life, this forms pearls in some Asian sea species.

  23. Mantle Layers

  24. Mollusca Comparative Forms Foot – Shell – Mantle – Visceral Mass

  25. Form & Function • Internal Structure and Function of Organs • Circulatory system: • Gastropods (Snails & Slugs) and bivalves (Clams and Oysters) have an open circulatory system consisting of a pumping heart, vessels and sinus • Squid, octopuses and nautilus have a closed circulatory system consisting of a heart, vessels and capillaries

  26. Form & Function • Reproduction • Most molluscs are dioecious but some are hermaphroditic • In most marine and freshwater species, the egg hatches into a larvae and then grows into an intermediate stage, the veliger which has the beginning of a head, foot and shell • In cephalopods, snails, and some freshwater bivalves, there is no larval stage and the egg hatches in a juvenile Veliger (larval form)

  27. CLASSES OF MOLLUSCSTHERE ARE SEVEN CLASSES BUT WE WILL ONLY STUDY THREE • Class Gastropoda-the largest and most diverse class of phylum Mollusca • Contains 40,000 living species and 15,000 fossil species • Includes snails, slugs, limpets, whelks, conchs, sea slugs, sea hares, and sea butterflies. • They range from primitive marine forms to highly developed air breathing terrestrial snails and slugs

  28. slugs snails whelks conchs limpets

  29. Sea slugs Sea hares Sea butterflies

  30. GASTROPOD SHELLS D. 1. one piece shell sometimes coiled or twisted 2. the apex is the smallest and oldest whorl 3. the shell may be a right-handed spiral (dextral) or left-handed spiral(sinstral) direction of coiling is genetically determined. 4. In many snails, the shell is closed by an operculum a small trap door. E. Terrestrial gastropods are restricted by mineral content, Temperature, dryness, and acidity

  31. TORSION F. In phylum Mollusca, only gastropods undergo the strange phenomenon of Torsion. 1. torsion is caused by the muscles of the left and right sides of the body grow at different rates. 2. torsion causes the organs to shift through a 90 degree to 180 degree rotation while in the veliger stage. 3. this causes the anus to move over the mouth and head 4. the nervous system is twisted into a figure eight.

  32. DIAGRAM OF TORSION IN GASTROPODS

  33. ADVANTAGES AND DISADVANTAGES OF TORSION 5a. The advantage is that the head can be retracted into the shell because of the space available in the mantle cavity. 5b. The disadvantages are that waste is released by the anus over the head and mouth and this could lead to a serious fouling problem. Also, one gill or lung, auricle of heart, and kidney is lost in this process, in most species. Usually, the absence of one gill solves the problem of fouling. The anus empties on that side.

  34. COILING OF THE SHELL • Coiling of the shell is a different process, but it happens in the larval stages. • All Gastropods evolved from tortedand coiled ancestors, even ones like slugs H. Feeding Habits 1. All possess a Radula 2. many are herbivores, some scavenge on decaying flesh and others are active predators that tear prey with the radula. 3. some collect debris in a mucus ball 4. some eat bacteria that collects in their slime trails

  35. MAJOR GROUPS OF GASTROPODS • 1. Prosobranchsinclude Abalone, conchs, whelks, limpets and murex a. have one pair of tenacles, are dioecious b. usually have an operculum abalone whelks murex

  36. MAJOR GROUPS OF GASTROPODS, CONTINUED 2. OPISTOBRANCHS Include sea slugs, sea hares, and sea butterflies a. all are marine b. live in shallow water c. two pairs of tenacles d.aremonoecious e. the shell is reduced or absent Sea hares Sea slugs sea butterflies

  37. MAJOR GROUPS OF GASTROPODS, CONTINUED 3. PULMONATESare all the terrestrial and most freshwater snails and slugs a. gills are modified into a lung b. are all monoecious c. aquatic forms have one pair of retractable tentacles and terrestrial forms have two pair of tentacles with the posterior pair carrying a set of eyes d. there are thousands of species of land snail

  38. GENERALIZED GASTROPOD ANATOMY

  39. Class Bivalva 1. This class includes mussels, clams, scallops, oysters and shipworms

  40. Class Bivalva Oysters Clams Mussels Shipworms Scallops

  41. Class Bivalva 2. They range in size from 2mm up to the Giant Clam of the South Pacific with a size of 1 meter in length and 650 kg

  42. Class Bivalva 3. Most are filter feeders • Most are marine, some live in brackish water • The most endangered group of molluscs are freshwater clams, where of more than 300 species, 12 are extinct, 42 endangered and 88 threatened • Zebra mussels are a problem in the waterways of the U.S. Zebra Mussels

  43. Form & Function • The organism is made up of 2 shells called valves held together by a hinge ligament

  44. Form & Function B. The oldest part of the shell is called the umbo with the growth outward in rings

  45. Form & Function C. The shell is produced by the mantle 1.)Pearls are produced when an irritant is lodged between the shell and the mantle

  46. Locomotion • Occurs when the muscular foot is protruded between the shells and it can pull the shell forward • Some shellfish can clap their shell together and move through jet propulsion

  47. Feeding Habits • Most are filter feeders and draw in organic material with an incurrent and excurrent siphon

  48. Feeding Habits B. Shipworms excavate particles of wood & feed on them C. One group, draws in small crustaceans by creating a flow of water into the shell

  49. Sense Organs • Some bivalves have tentacles on the edge of the mantle • Some have blue eyes around the edge of the mantle

  50. Reproduction • Sexes are usually separate (dioecious) • Gametes are carried out the excurrent siphon • Fertilization is external • Embryos develop both trochophore and veliger larval stages • Freshwater clams have internal fertilization where the sperm is drawn into the female’s body with incurrent flow of water – eggs hatch inside the shell & veliger larvae are discharged by excurrent flow

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