Evolution of Mollusca

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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