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Diagram of primitive mollusc viewed from left side. Hypothetical mollusc ancestor. From Encyclopædia Britannica Eleventh Edition.

The current understanding of molluscan phylogeny is shown below.

Horizontal cladogram (source: ^[1]):

Mollusca molluscs
  |
  +-- Aplacophora
  |     |
  |     +-- Solenogastres
  |     +-- Caudofoeveata
  |
  +-- Testaria
        |
        +-- Polyplacophora - chitons
        |     |
        |     +-- Palaeoloricata
        |     +-- Neoloricata
        |
        +-- Conchifera
             |
             +-- Monoplacophora
             |
             +--+
                |
                +--Cyrtosoma
                |     |
                |     +-- Gastropoda - gastropods
                |     |
                |     +-- Cephalopoda - cephalopods
                +-- Diasoma
                      |
                      +-- Rostroconchia
                      |
                      +--+
                         |
                         +-- Scaphopoda - tusk shells
                         |
                         +-- Bivalvia - bivalves

Early organisms which have been compared to molluscs include Kimberella and Odontogriphus.

References

Further reading

• From sea to land and beyond – New insights into the evolution of euthyneuran Gastropoda (Mollusca)

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