A new taxonomic and zoogeographic interpretation of the Diacria quadridentata group (Mollusca, Pteropoda)

Re-examination of the Diacria quadridentata species group based upon morphology of the shell and zoogeographic data, led to a new classification comprising the recent taxa: D. quadridentata, D. costata with an equatorial and a central water form, D. danae with an equatorial and a central water form, D. schmidti schmidti, D. erythra crassa and the fossil taxa D. schmidti cocidentalis and D. erythra erythra from surface sediments. A method has been developed to estimate the relative age of the population, based on the development of shell and soft parts. Shell growth in the period of minute and adult stages together does not exceed 0.2 mm, and differs from species to species.