Mollusca		Eogastropoda
GASTROPODA		Euomphalida

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Euomphalida

Gastropoda (crown group)  
|--EOGASTROPODA  
|  |-?OPHILETOIDEA
|  `--+--MACLURITOIDEA
|     `--+--EUOMPHALIDA  
|        |--PLATYCERATOIDEA  
|        |--NEOMPHALIDA  
|        `--Patellogastropoda
`--Orthogastropoda  

Introduction

o Eogastropoda
`--o Ophiletidae
   |--+-- Macluritoidea
   |  |  ? --Omphalocirridae 
   |  |--o Helicotomidae
   |  |  `--+--o Anomphalidae
   |  |      `--o Euomphalidae
   |  |         `--o Pseudophoridae
   |  |  ? --Omphalotrochidae
   |  `--o Lesueurillidae
   |  ? --Planitrochidae
   `--+-- "Lytospiridae"
      `--o Euomphaloidea (in part)
         `--o Raphistomatidae
            `--o Platyceratoidea
               `--o Holopeidae
                  `-- Platyceratidae
            ? --Metoptomatidae
                ? -- Patellogastropoda
                    ? --Cocculiniformia

The Euomphalids (originally Euomphalacea or Euomphalina ) are an important Paleozoic clade of low-spired to planispiral gastropods, some of which, like the macluritids, are hyperstrophic. They are very abundant in some Paleozoic formations and include useful index fossils.  Moore, et al. (1952). Some lived lifestyles like modern gastropods, others it seems were sedentary filter-feeders.

The group was originally considered a superfamily of Archaeogastropoda, and according to Knight et al. (1954), evolved from macluritids, with which they seem to be clearly related. Linsley & Kier (1984) tentatively place them, along with the Macluritoidea, in the Paragastropoda.  But Wagner (1999) derives both groups from ophiletids, although they seem to have diverged very early.

The group as originally defined had two peaks of development, one in the Devonian and another in the Triassic (finally dying out in the Cretaceous) , but these would seem to be actually two distinct stocks.  Moore, et al. (1952).  The Palaeozoic forms are true Euomphalids, whereas the Mesozoic taxa appear to be derived trochoids.  Bandel (1988).  Examination of shell mineralogy, larval shells, and teleoconchs (adult shells) confirm that the Euomphalacea/Euomphaloidea, like the Bellerophontida and other extinct taxa, are polyphyletic.  Wagner (2001).

Not only are many species formerly considered Euomphalids not really related, but it seems that other forms that have previously been thought of as having different origins actually are. Studies also indicate that many Paleozoic Palaeotrochoidea (placed in the Trochina -- now included in the Vetigastropoda -- by Knight, et al., 1960) are a polyphyletic assemblage related to the euomphaloids.  Wagner (2001).  Ponder and Lindberg (1996, 1997) suggest that palaeotrochoids and vet gastropod trochoids are only distantly related. According to Wagner (1999), both palaeotrochoids and traditionally placed euomphaloid planispiral taxa arose at least six times each in the Ordovician and Silurian, mostly within the same clade.  Wagner (2001).

note: in keeping with the convention of the Treatise authors of the volumes on Gastropoda and Cephalopoda, the suffix -ina is used for suborders, and -ida for orders. Since the Euomphalida are here considered of ordinal rank, the previous suffix -ina has been changed accordingly

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