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Phylum Mollusca > 100,000 extant species

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Presentation on theme: "Phylum Mollusca > 100,000 extant species"— 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 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


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