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Phylum Mollusca

Phylum Mollusca. Molluscan diversity. Adapted from Lesser Known Protostome Phyla. SICB 2001. J.R. Garey. Porifera. Cnidaria. Ctenophora. Platyhelminthes. Gastrotricha. Gnathostomulida. Cycliophora. Rotifera. Annelida. Mollusca. Sipuncula. Nemertea. Bryozoa. Brachiopoda. Phoronida.

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Phylum Mollusca

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  1. Phylum Mollusca

  2. Molluscan diversity

  3. Adapted from Lesser Known ProtostomePhyla. SICB 2001. J.R. Garey. Porifera Cnidaria Ctenophora Platyhelminthes Gastrotricha Gnathostomulida Cycliophora Rotifera Annelida Mollusca Sipuncula Nemertea Bryozoa Brachiopoda Phoronida Arthropoda Onychophora Tardigrada Nematomorpha Nematoda Priapulida Kinorhyncha Loricifera Echinodermata Hemichordata Chordata Possess trochophore larvae Mollusca and Annelida are closely allied phyla

  4. Arthropoda Mollusca Chordata Platyhelminthes Nematoda Annelida Porifera Echinodermata Other Sarcomastigophora Apicomplex Ciliophora 93,000 species of described molluscs (extant) + 70,000 more species from fossil record

  5. Defining characteristics of Mollusca • Bilateral symmetry, cephalization • Coelom (around heart) • Mantle • draped over viscera • secretes shell • Complete digestive tract, Radula • Trochophore larvae (often also veliger larvae) • Locomotion by muscular foot • Heart, liver, gills (ctenidia), kidney

  6. Phylum. Mollusca Class. Aplacophora Class. Polyplacophora Class. Monoplacophora Class. Gastropoda Class. Cephalopoda Class. Bivalvia Class. Scaphopoda

  7. Monoplacophora Cephalopoda Gastropoda Bivalvia Scaphopoda Polyplacophora Aplacophora

  8. Mollusc origins? Platyhelminthe-like ancestor with spicules on dorsal surface, cilia on ventral surface, and dorsoventral musculature.

  9. Mollusc origins? Spicules fuse to form dorsal shell, cilia on ventral surface, and dorsoventral musculature.

  10. Mollusc origins? Spicules fuse to form dorsal shell, cilia on ventral surface, dorsoventral musculature, gonads and excretory pores in mantle cavity

  11. Mollusc origins? Spicules fuse to form dorsal shell, cilia on ventral surface, dorsoventral musculature, gonads, excretory pores, and ctenidia, in mantle cavity.

  12. HAM: Hypothetical ancestral mollusc Pericardial cavity Metanephridium Mantle cavity Gonad Ctenidium Radula Foot Stomach and digestive gland

  13. Dorsal mantle covers the visceral mass. Secretes the shell

  14. Mollusc shell Periostracum Prismatic layer Nacreous layer Mantle epithelium Mantle lobes

  15. Pearl formation Periostracum Prismatic layer Nacreous layer Developing pearl Epithelium

  16. Ctenidium (Respiration)

  17. Ctenidium (gill) Interlamellar junctions Exhalent water Ostium Blood vessel Frontal cilia

  18. Paired ventral nerve cords

  19. Complete digestive system

  20. Radula

  21. Radula

  22. Aplacophora Mouth Gill folds Pedal pit Pedal groove

  23. Class Aplacophora • 320 spp, all marine • No fossil record (!) & poorly studied • Calcareous spines and scales in epidermis (no true shell) • Radula used for grasping • Burrow in the substrate • Eat cnidarians

  24. Polyplacophora

  25. Polyplacophora Mouth Mantle cavity Ctenidium Foot Anus

  26. Polyplacophora Stomach Gonad Digestive gland Pericardial cavity Mouth Nephridium Anus

  27. Polyplacophora • The “chitons” • 800 spp, marine • Typically, shell = 8 dorsal plates • Ctenidia use counter-current gas exchange • Commonly encountered in the intertidal zone

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