Mollusca

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What is a mollusc? Fundamental organization : - shell secreted by a layer of tissue called the mantle - mouth and anus at opposite end (but in gastropods both anterior) - mantle cavity bears gills (but pulmonate gastropods have no gills) - above mantle cavity is the visceral mass with gut, nervous, circulatory and muscular system - muscular foot facilitates movement - shell is of calcium carbonate (calcite or aragonite) (but may be secondaryly lost) - shell typically external (but in some groups it became internal) - grow by accretion (calcium carbonate is added to the edge of the shell by the mantle) - generally marine (but also few freshwater and terrestrial groups) <strong>Mollusca</strong>
Typical features: Shell Strongly mineralised = hard 1-2 components (up to 8) Simple, compact shapes Usually coiled to some degree = Facilitates excellent fossil record No other animal group can compete!
Page 1 and 2: mollusks Mollusca blötdjur mollusc
Page 3: general things Mollusca Mollusca
Page 7 and 8: Typical features: Radula Most mollu
Page 9 and 10: Tryblidiida (”monoplacophorans”
Page 12: Polyplacophora (chitons) primitive
Page 15: Bivalvia (=Pelecypoda, Lamellibranc
Page 19 and 20: Scaphopoda (tusk shells) small gro
Page 21 and 22: Helcionellida (Cambrian-Ordovician)
Page 23 and 24: Rostrochonchia single, pseudobival
Page 25 and 26: Hyolitha Probable molluscs Early
Page 27: Mollusca Protostomes Part of the
Page 31 and 32: What’s the problem?
Page 33: What’s the problem? D C B A The H
Page 36 and 37: Precambrian Mollusca Mollusca
Page 38 and 39: Ediacaran Substrate Very stable sof
Page 41 and 42: Typical features: Radula Most mollu
Page 44: Helcionellida laterally compressed
Page 51 and 52: But what about the phylogeny? Molec
Page 53 and 54: Aplacophora (solenogastres) No she
Page 55 and 56:
Acaenoplax Possible caudofoveate f
Page 57 and 58:
Chancelloriids Star shaped sclerit
Page 59 and 60:
Halkieriids Articulated specimens
Page 61 and 62:
Odontogriphus
Page 63 and 64:
Halwaxiids Mollusc-like unmineral
Page 66:
Conchifera = -Bivalvia -Gastropoda
Page 69 and 70:
Tryblidiida (”monoplacophorans”
Page 71 and 72:
Rostrochonchia single, pseudobival
Page 73 and 74:
Helcionellida endogastric Mollusca
Page 75 and 76:
Hyolitha Probable molluscs Early
Page 77 and 78:
Orthothecid (Conotheca)
Page 79:
Hyoliths in stomach of Ottoia
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Mollusca

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