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 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 3. Broad, ventral foot
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 cm long
Largest is Epimenia verrucova; 30 cm
All marine
Mostly deep waters, 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