Palæos:		Mollusca
METAZOA		Cladograms

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Molluscan Cladograms

Lophotrochozoa |--MOLLUSCA | BASAL MOLLUSCA | |--Diasoma | | |--Rostroconchia | | `--BIVALVIA | | |--Protobranchia | | `--HETERODONTA | `--CYRTOSOMA | |--CEPHALOPODA | `--GASTROPODA | |--Eogastropoda | `--APOGASTROPODA | |--Caenogastropoda | `--HETEROBRANCHIA | |--Opisthobranchia | `--PULMONATA `--ANNELIDA

Working Phylogeny   Tentative Molluscan Phylogeny

Working Phylogeny

Our working phylogeny of the mollusks differe somewhat from Alan's Phylogeny below, probably because Alan actually thought about it, while we were more concerned with matters of format.  Directory structure on the web enforces a species of heirarchical, somewhat Linnean, organization which is sometimes antithetical to good phylogenetics.   It doesn't have to be this way, but we are all heirs to the legacy of DOS -- and Aristotle, for that matter.  In any event, our working phylogeny (much abbreviated and coded to match our current directory structure) looks like this:

MOLLUSCA
|
BASAL MOLLUSCA
|--Aplacophora  
`--Testaria  
   |--Polyplacophora  
   `--Conchifera (Helcionelloida)  
      |--Monoplacophora  
      `--+--Diasoma  
         |  |--Rostroconchia 
         |  `--BIVALVIA
         `--+--CYRTOSOMA  
            |  |--Scaphopoda  
            |  `--Cephalopoda  
            |     |--Nautiloidea  
            |     `--Neocephalopoda  
            |        |--Ammonoidea  
            |        `--Coleoidea  
            `--GASTROPODA (stem group) 
               |--Paragastropoda  
               `--Tergomya (grossly paraphyletic)  
                  |
                  Gastropoda (crown group)  
                  |--Eogastropoda  
                  |  |--Euomphalida  
                  |  `--Patellogastropoda  
                  `--Orthogastropoda  
                     |--Vetigastropoda  
                     `--APOGASTROPODA  
                        |--Caenogastropoda  
                        `--HETEROBRANCHIA  
                           |--Opisthobranchia  
                           `--PULMONATA  

 

Tentative Molluscan Phylogeny

The following cladogram is based on a number of sources, as well as arguments presented in these pages regarding some of the more radical placements. The position of the Bivalvia remains controversial. On the basis of molecular and some cladistic evidence, it belongs near the bottom of the conchiferan crown group, possibly prior to the Helcionellid-derived Gastropoda + Cephalopoda + Scaphopoda clade).  But on the basis of cladistic evidence from transitional Cambrian forms, Bivalvia is much closer to the Rostrochochia. The Scaphopoda are here derived from the Rostrochonchia, with the Cephalopoda very tentatively derived from related Yochelcionellid Helcionellids.

<==o MOLLUSCA
   `--+--o SOLENOGASTRES
      `--+--+-- †Acaenoplax hayae
         |  `--o CAUDOFOVEATA
         |     |-- Limifossoridae
         |     |-- Prochaetodermatidae
         |     `-- Chaetodermatidae
         `--o TESTARIA 
            `--+--o POLYPLACOPHORA 
               |  `--+--†Mattheviidae
               |     |--†Septemchitonida
               |     `--+--†Chelonida
               |        `--+--Lepidopleurida
               |            |--†Scanochitonida
               |            `--Chitonida
               `--o CONCHIFERA 
                  |--o Tryblidiida ("Tergomya" in part)
                  |  `--o Tryblidoidea
                  |     `-- Neopilinidae
                  | ?-- STENOTHECOIDA
                  `--+--?? BIVALVIA (on basis of molecular phylogeny)
                     `--o Unnamed Clade (Higher Conchifera)
                        `--o †Helcionellidae (Helcionelloida)
                           |--+--+-- †Yochelcionellidae [Helcionelloida = "Quasirostroconchs"]
                           |  |  `?-- CEPHALOPODA
                           |  | ? -- †CRICOCONARIDA  
                           |  `--+--†Stenothecidae [Helcionelloida; = "Pararostroconchs"]
                           |     |--+--+-- †Heraultipegma varensalense
                           |     |  |  `-- †Watsonella crosbyi
                           |     |  `--? BIVALVIA (on basis of transitional forms)
                           |     `--+--+-- †Taurangia paparua
                           |        |  `-- †Pseudomyona queenslandica
                           |        `--+-- †ROSTROCONCHIA
                           |           `-- SCAPHOPODA 
                           | ?-- †Palaeacmaeidae
                           |--+-- †Helcionella subrugosa
                           |  `--+--†Helcionella subrugosa comleyensis
                           |     `--o †Scenellidae (Helcionelloida)
                           |        `--+-- †Scenella reticulata
                           |           `-- †Kiringella pyramidalis "Tergomya"
                           `--+--†Coreospiridae (Helcionelloida)
                              |--+-- †Euomphalopsis involuta
                              |  `-- †Macluritella? walcotti
                              |--o †PARAGASTROPODA
                              |  |--o †Pelagielloidea
                              |  `--o †Onychochilioidea
                              |?-- †Hypseloconoidea "Tergomya"
                              `--+-- †Cyrtolites "Tergomya"
                                 `-+-- †Chippeaella patellitheca
                                   `-- GASTROPODA