Die systematische Stellung der Euomphalidae (Gastropoda)

Abstract

The core group of Euomphalidae with the genera Euomphalus, Straparollus, Serpulospira, Phymatifer, Schizostoma, Nodeuomphalus n. g. (Devonian to Permian) are characterized by a cyrtoconic, openly coiled, planispiral protoconch. This character distinguishes them from members of the four extant subclasses of the Gastropoda (Archaeogastropoda, Neritimorpha, Caenogastropoda and Heterostropha) and places the Euomphaloidea at a similarly high taxonomic level, the new subclass Euomphalomorpha. With Euomphalopsis the group may have made its first appearanee in the Late Cambrian, and it is certainly present from the Mid Devonian to Late Permian and thus the range is about 300 million years in duration. Throughout the existence of the Euomphaloidea other gastropod units developed convergent shell forros which can be detected by the morphology of the protoconch and, in well preserved fossils, the mineralogical and stmctural composition of the she[l. The new taxa Euomphalomorpha n. subclassis, Nodeuomphalus n, g., N. paffrathianus n. sp., and "Ptanerotinus "" scheeri n. sp. are describe& K e y w o r d s : Gastropoda, Euomphalidae, taxonomy, protoconch, Paleozoic. Kurzfassung[Die systematische Stellung der Euomphalidae (Gastropoda).]-Den Kernbereich der Familie Euomphalidae stellen die Gattungen Euomphalus, Straparollus, Serpulospira, Phymatifer, Schizostoma und Nodeuomphalus aus dem Zeitraum Devon bis Perro. Sie werden durch einen Protoconch gekennzeichnet, der mit einer eif'6rmigen Anfangskalotte ausgestattet ist, an die sich eine erste offene Windung anschlieBt. Dadurch verbleibt eine zentrale Offnung im Inneren der ersten planspiraligen Windung sichtbar im Apex der Schale. Dieser Protoconch unterscheidet die neue Unterklasse Euomphalomorpha von den auch heute noch existenten Unterklassen der Gastropoda, den Archaeogastropoda, Neritimorpha, Heterostropha und Caenogastropoda. Mit Euomphalopsis war m6glicherweise schon ira sp/iten Kambrium ein Vertreter der Euomphalomorpha present. Vertreter der Gruppe sind vom Mitteldevon bis zum spfiten Perm gesichert nachzuweisen. Schon seit dem Ordovizium treten innerhalb anderer Gastropoden-Taxa konvergente Arten auf, so daB nur bei einer Erhaltung des Protoconches, oder auch der Schalenstruktur, Euomphalomorpha gesichert erkannt werden k6nnen. Die neuen Taxa Euomphalomorpha n. subclassis, Nodeuomphalus n. g., AL pafJ?athianus n. sp., and ,, Planerotinus" scheeri n. sp. werden beschrieben.

An Evaluation of the Recently Proposed Palaeozoic Gastropod Subclass Euomphalomorpha

“…The protoconch of modern archaeogastropods was discussed by Bandel (1982) and Haszprunar (1993); the latter referred to it as the trochoid condition. Generally, the concept of the classical archaeogastropods is currently more that of a grade rather than a clade (Hickman 1988;Haszprunar 1993).…”

“…Generally, the concept of the classical archaeogastropods is currently more that of a grade rather than a clade (Hickman 1988;Haszprunar 1993). Bandel (1982) showed that modern archaeogastropods, unlike all other Recent gastropods, have an unmineralized, bilaterally symmetrical shell, which is mechanically deformed and then mineralized. This commonly results in a characteristic irregular spiral shape and the presence of pouches, which are typical for many archaeogastropod protoconchs.…”

Gastropods from the Early/Middle Jurassic transition of Franconia (Southern Germany)

“…-Szabó (2009) discussed the systematic placement of discohelicids in detail and placed this group in Euomphalina and Euomphalina in Vetigastropoda (see also Bandel & Frýda 1998, Nützel 2002a). The present representative Discohelix guembeli adds no new information about the debated relationships of Palaeozoic euomphalids and Mesozoic discohelicids.…”

Crystallographic texture of Late Triassic gastropod nacre: evidence of long-term stability of the mechanism controlling its formation

“…Thus all living vetigastropods lacking nacre originated after the Paleozoic time. The phylogenetic position of the extinct Euomphaloidea is uncertain (Bandel & Frýda 1998;Nützel 2002;Frýda et al , 2008a. There is no reason to place them, together with all other extinct Paleozoic archaeogastropod families, within the Vetigastropoda because the latter clade is diagnosed by anatomic features that cannot be examined in extinct groups.…”

“…Paleozoic Euomphaloidea as well as Macluritoidea may represent basal or sister taxa to the Archaeogastropoda (also including Vetigastropoda) as shown by their protoconch morphology (Frýda & Rohr 2006). The members of the first group lack nacre (Bandel & Frýda 1998), but there are no shell microstructure data for macluritoidean gastropods.…”