The Vetigastropoda and the systematics of streptoneurous Gastropoda (Mollusca)

Abstract

The status of the Vetigastropoda, created 1980 to unite zeugobranch and trochoid archaeo‐gastropods, is reconsidered and confirmed in the light of recent investigations. The most important synapomorphic characters of the Vetigastropoda are the ctenidial sense organs (so‐called bursicles), the epipodial sense organs, and the special structure of the oesophagus. The conditions of the archaeogastropod oesophagus are comparatively described. An examination of the relationships of the Vetigastropoda establishes the archaeogastropod nature of the Architaenioglossa. It also demonstrates the monophyletic origin of all higher gastropods, including the Caenogastropoda (s.str.) as well as the Pentaganglionata (= Euthy‐neura). The Campanilidae, Valvatidae, Rissoellidae, Omalogyridae, and the Allogastropoda (= Architectonicoidea and Pyramidelloidea) share characteristics with both of the above‐mentioned groups, but cannot be classified within any of them. These groups are regarded as subsequent offshoots between the caenogastropod and the pentaganglionate level of organization. The level of Archaeogastropoda is redefined by the hypoathroid/dystenoid nervous system and simple tentacle nerves; the remaining Streptoneura are classified as Apogastropoda with epiathroid nervous system, parapedal commissure, and bifurcated tentacle nerves.