Mathildoidea (Gastropoda, Heterostropha) from the Late Triassic St Cassian Formation
In the St Cassian fauna of Late Triassic (Early Carnian) age gastropods with protoconch coiled in opposite direction to the teleoconch are common and belong to a number of quite different taxa. Twenty nine of these are here described, 11 of them for the first time: Promathilda misurinensis sp. nov., Turrithilda cassiana sp. nov., T. dockeryi sp. nov., Tirolthilda seelandica gen. et sp. nov., T. nuetzeli sp. nov., Tofanella cancellata sp. nov., Cristalloella cassiana gen. et sp. nov., C. sinuata sp. nov., C. delicata sp. nov., Stuorilda cassiana gen. et sp. nov., and S. tichyi sp. nov. All are newly defined and placed in the Mathildoidea. This connects the Triassic species of that superfamily with the modern Heterostropha (= Heterobranchia). In the family Mathildidae the genera Mathilda and Promathilda are differentiated, two species of Turrithilda described, and Tirolthilda and Schroederilda are included as new genera, with the type species T. seelandica gen. et sp. nov. and Pseudotritonium millierense Zardini, 1978, respectively. The new family Anoptychiidae holds the genera Anoptychia, Turristylus and Camponella gen. nov. (type species Coelostylina pianozensis Zardini, 1985). Here the juvenile ornament resembles that of the Mathildidae but differs from the later smooth teleoconch. Protoconch morphology differentiates the new families Tofanellidae, Trachoecidae and Ampezzanildidae. In contrast to the Mathildidae, Dolomitellidae and Anoptychiidae, the sinistral shell of the protoconch changes its direction of coiling within the larval part of the shell and not at the transition from larval shell to teleoconch. The Trachoecidae with the genera Trachoecus and Vallandroella gen. nov. (type species Tyrsoecus antorni Zardini, 1985) have a fusiniform shell. The Tofanellidae, with the genera Tofanella gen. nov. (type species Turritella decussata von Münster, 1841), Cristalloella gen. nov. (type species C. cassiana gen. et sp. nov.) and Camponaxis gen. nov. [type species Cerithium (?) lateplicatum Klipstein, 1843], differ from the Ampezzanildidae, with the genera Ampezzanilda gen. nov. (type species Promathildia aialensis Zardini, 1980), Cassianilda gen. nov. (type species Turritella margaritifera von Münster, 1841) and Stuorilda gen. nov. (type species S. cassiana gen. et sp. nov.), by the ornament of their protoconch. A key differentiates all described species, and the evolutionary history of the group is discussed.
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Bandel, K. (1995). Mathildoidea (Gastropoda, Heterostropha) from the Late Triassic St Cassian Formation. Scripta Geologica, 111, 1–83.