1 / 42

Phylum Mollusca

Phylum Mollusca. > 100,000 extant species At least 45,000 extinct species Nice fossil history based on shells Fossils from Pre-Cambrian Importance? Shells - collectors, jewelry food. Mollusca characteristics:. 1. Foot 2. Mantle 3. Secretes shell. Shell: 3 layers.

hayward
Download Presentation

Phylum Mollusca

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Phylum Mollusca • > 100,000 extant species • At least 45,000 extinct species • Nice fossil history based on shells • Fossils from Pre-Cambrian • Importance? • Shells - collectors, jewelry • food

  2. Mollusca characteristics: • 1. Foot • 2. Mantle • 3. Secretes shell

  3. Shell: 3 layers

  4. Periostracum: horny protein, conchiolin in some

  5. Prismatic layer: calcite crystals w/membranes between

  6. Nacreous layer: CaCo3

  7. Mollusca characteristics: • 1. Foot • 2. Mantle • 3. Secretes shell • 4. External surfaces - ciliated epidermis w/ mucous glands • Food capture, feeding, locomotion, cleaning body surfaces

  8. Cilia move mucous and create water flow • Gas exchange + bring food in • Sorting surfaces separate food particles by size

  9. Cilia over gill surface • Water movement opposite of blood flow

  10. 5. Coelom is reduced • Only pericardial cavity

  11. 6. Open circulatory system • Blood sinuses (no capillaries) • Heart = one or two auricles • collecting chambers • one ventricle • pumping chamber

  12. More circ. system • Hemocyanin pigment in blood (copper) • Blood w/ O2 = blue • Blood w/o O2 = colorless • Pulmonate gastropods have hemoglobin • Cephalopods have closed circulatory system

  13. 7. Digestive system • Sclerotized buccal cavity • Tubular esophagus • Cone-shaped stomach • Long, coiled intestine

  14. Radula • Chitin-toothed • Rasping organ for scraping algae

  15. Stomach • Contains style sac, rotates contents • Pulls strands of mucous from esophagus • Mucous viscosity decreases w/ low pH • Stomach wall is chitinized • Crystalline rod = hyaline mucoprotein • Style has hydrolase digestive enzymes

  16. Stomach, cont. • Sort food particles by size • Intracellular digestion in digestive gland walls • Some extracellular dig. in stomach • Carnivores have no style

  17. Sorting in stomach

  18. Intestine • Fecal compaction • Anus opens into mantle cavity

  19. 8. Nitrogenous waste • Pair of coelomoducts • Open to pericardial cavity • Discharge into mantle cavity via nephridiopores • Probably not homologous to annelid metanephridia (annelid origin = mesoderm; mollusk origin = ectoderm)

  20. Waste product? • Ammonia in aquatic molluscs • Uric acid in terrestrial molluscs

  21. 9. Nervous system - varied • Polyplacophora (chitons) - decentralized, no ganglia • Cephalopods - as developed as in vert’s • Primitive gastropods: • Nerve ring around esophagus, 2 pair of major nerve cords

  22. Reproduction and development • Pair of gonads in coelom • Eggs + sperm into pericardial cavity, outside via coelomoducts • Fert external in sea water • Molluscs mostly dioecious, some gastropods hermaphroditic

  23. Most gastropods, all cephalopods: • Sperm transferred to female’s mantle cavity • Internal fertilization • Hermaphroditic gastropods do reciprocal cross-fertilization

  24. Development • Trochophore larvae = free-swimming eye stomach prototroch ciliated band mouth intestine protonephridium anus

  25. Trochophore larvae • Archaeogastropoda • Polyplacophora • Aplacophora • Most marine bivalves • Develops into veliger larvae • Foot, shell, other structures appear

  26. Phylogenetic significance of trochophore larvae • Hatschik (1878) • Present in molluscs, annelids, other phyla • Promotes ctenophora - trochophore theory of bilateral animals from radial ancestors • body shape, apical sense organs, statocysts, nervous systems

  27. Problem with ctenophora-trochophore connection • Flatworms don’t fit • Degenerate annelids?

  28. 7 mollusca classes • Polyplacophora • Aplacophora • Monoplacophora • Gastropoda • Scaphopoda • Bivalvia • Cephalopoda

  29. Class Polyplacophora • Chitons and oval-flattened beasts - mostly in rocky intertidal zones • All marine, ~ 800 spp. • Mostly 2 - 12 cm • Largest (30 cm)is Cryptochiton stelleri from N. Pacific coast of N. America = Pacific gumshoe chiton

  30. Chiton characteristics: • Most feed on algae and micro-organisms on rock surfaces • Few are predators on small inverts • 1. Rudimentary head • No tentacles or eyes

  31. Characters • 2. Mantle covers dorsal surface • Secretes 8-piece shell • 3. Broad, ventral foot • 4. Many paired gills in mantle cavity • 5. Anterior mouth with radula

  32. Repro: • 6. Dioecious • trochophore larvae, no veliger • external fert. in sea water mouth Gills in mantle cavity mantle foot

  33. Classification of Polyplacophora - 2 orders • Order Lepidopleurida: few genera, Hanleya NE coast • Order Chitonida - most chitons • Chaetopleura (New England - Fl) • Chiton (gulf coast) • Katherina (N. Pacific coast) • Cryptochiton (N. Pacific coast) • Mopalia • Ishnochiton

  34. Class Aplacophora • Solenogasters are worm-like molluscs 0.5 - 30 cm long • Largest is Epimenia verrucova; 30 cm • All marine • Mostly deep waters, 20 - 9000 m • Some crawl and feed on hydroids and corals • Poorly known, seldom seen, ~ 250 spp.

  35. Characteristics: • 1. Worm-like body shape • 2. No shell, mantle, or foot • 3. Cuticle w/layers of imbedded calcareous spicules • 4. Ventral surface has longitudinal pedal groove • 5. Hermaphroditic • 6. Radula well-developed

  36. Pedal groove cloaca

  37. Class Monoplacophora • Originally known only from fossils • Living Neopalina from 3600 m in Pacific Ocean coast of Costa Rica (1952) • Two genera • Neopalina (7 spp.) and Vema

  38. Characteristics: • 1. Dorsal surface covered by flat conical shell. • 2. Ventral surface with mantle, paired gills and foot. • 3. Multiple paired gills, coelomoducts, heart chambers, gonads, and retractor muscles.

  39. Neopalina: Dorsal Ventral

  40. Dissection: bivalve umbo anterior

  41. Remove valve

More Related