Mollusca		CONCHIFERA
Basal Mollusca		Cladogram

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Helcionelloida (Basal Conchifera) Cladogram

BASAL MOLLUSCA |--APLACOPHORA `--TESTARIA |--POLYPLACOPHORA `--CONCHIFERA (Helcionelloida) |--Scenellidae `--+--Helcionellidae |?-Yochelcionellidae |?-Stenothecidae |?-Coresopiridae |--MONOPLACOPHORA `--+--DIASOMA | |--ROSTROCONCHIA | `--Bivalvia `--Cyrtosoma

Helcionelloid Phylogeny      Wagner Cladogram      Modified Cladogram   References

Helcionelloid Phylogeny

Wagner Cladogram

The following cladogram is gives the relationship between Helcionelloids and derived taxa according to
Peter Wagner's cladistic analysis. While the helcinelloids fit together well enough, there is clearly something wrong with the relationship between the derived taxa. Whereas both cladistic and molecular evidence (Waller, 1998; Steiner & Dreyer, 2002) indicates (Bivalvia, (Gastropoda (Scaphopoda, Cephalopoda))), what we see here - assuming the current interpretation that Scaphopods and Cephalopods both developed from laterally compressed helcionelloids, is (Helcionelloida (Bivalvia (Scaphopoda, Cephalopoda)) (Gastropoda )).

<==o HELCIONELLOIDA
   `--o-- Helcionellidae
      |-- Helcionella subrugosa
      |-- Oelandia rugosa
      |--+-- Latouchella merino
      |  `--+--+--Latouchella accordionata
      |     |  `--Latouchella penecyrano
      |     `--+--o Yochelcionellidae
      |        |  |--Eotebenna arctica
      |        |  `--+--Eotebenna pontifix
      |        |     |--Eotebenna papilio
      |        |     `--+--Eotebenna viviannae
      |        |       `--+--Yochelcionella daleki
      |        |            `--+--Yochelcionella cyrano
      |        |               `--Yochelcionella ostentata
      |        |            ?--o Crown Group CYRTOSOMA
      |        |               |-- SCAPHOPODA 
      |        |               |-- CRICOCONARIDA
      |        |               `-- CEPHALOPODA
      |        `--o DIASOMA
      |           `--o Stenothecidae
      |              |--Enigmaconus parvus
      |              |--Anabarella simesi
      |              `--+--Anabarella argus
      |                 `--+--Mellopegma georginensis
      |                    `--+--Eurekapegma cooperi
      |                       |-- ROSTROCONCHIA
      |                       `-- BIVALVIA
      `--o Stem Group CYRTOSOMA
         `--+--+-- Coreospiridae
            |  |-- Coreospira rugosa
            |  `-- Sinuella minuata
            |--+-- Unnamed Clade
            |  |-- Euomphalopsis involuta
            |  `-- Macluritella? walcotti
            |-- PARAGASTROPODA
            `--+-- "Tergomya"
               `-- GASTROPODA  (Crown Group CYRTOSOMA)

Modified Cladogram

The next cladogram modified the above by putting the earliest known genus, Latouchella at the base of the tree, and rejecting the Cyrtosoma-Diasoma hypothesis in favor of a seperate origin for the Bivalvia. The Cephalopoda are tentatively derived from yochelcionellid-like forms (Pojeta, 1980 suggests that a yochelcionellid-like Helcionelloid would be a good ancestor for the cephalopods). Following Runnegar & Jell (1976), Helcionella is considered an atypical member of the family Helcionellidae. Scenella is derived from Helcionella subrugosa comleyensis, and Kiringella is closely related to Scenella. Further, the Tergomya are not only paraphyletic but polyphyletic. This gives the following:

<==o HELCIONELLOIDA
   `-o Helcionellidae
     `--+-- Latouchella korobkovi
        |--+-- Latouchella merino
        |  `--+--+--Latouchella accordionata
        |     |  `--Latouchella penecyrano
        |     `--+--o Yochelcionellidae
        |        |  |--Eotebenna arctica
        |        |   `--+--Eotebenna pontifix
        |        |      |--Eotebenna papilio
        |        |      `--+--Eotebenna viviannae
        |        |         `--+--Yochelcionella daleki
        |        |            `--+--Yochelcionella cyrano
        |        |                `--+--Yochelcionella ostentata
        |        |                   `?-- CEPHALOPODA
        |        |    ?-- CRICOCONARIDA
        |        `--o Stenothecidae
        |           |--Enigmaconus parvus
        |           |--Anabarella simesi
        |           `--+--Anabarella argus
        |              `--+--Mellopegma georginensis
        |                 `--+--Eurekapegma cooperi
        |                    `--+-- ROSTROCONCHIA
        |                       `-- SCAPHOPODA 
        |-- Oelandia rugosa
        |--+- Helcionella subrugosa
        |  `--+--Helcionella subrugosa comleyensis
        |     `--o Scenellidae
        |        `--+-- Scenella reticulata
        |           `--o "TERGOMYA" (endogastric)
        |              `-- Kiringella pyramidalis
        `--+--+-- Coreospiridae
           |  |-- Coreospira rugosa
           |  `-- Sinuella minuata
           |--+-- Unnamed Clade
           |  |-- Euomphalopsis involuta
           |  `-- Macluritella? walcotti
           |-- PARAGASTROPODA
           `--+-- "TERGOMYA" (iexogastric)
              |--o Hypseloconoidea
              `--+-- Cyrtolites
                 `--+-- Chippeaella patellitheca
                    `--+-- Pretorted Bellerophontina
                       `-- GASTROPODA 

References