Euthecosomata (Mollusca, Gastropoda, Thecosomata). Taxonomic review

ABSTRACT The Euthecosomata Meisenheimer, 1905, holoplanktonic Mollusca with coiled or straight shell were respectively classified in Limacinoidea Gray, 1847 and Cavolinioidea Gray, 1850. In a biometrical analysis (Rampal 1973) a first change had occurd in this last superfamily: the conica shell genera Creseis Rang, 1828, Boasia Dall, 1889, Styliola Gray, 1850 and Hyalocylis Fol, 1875 were gathered into the Creseidae Rampal, 1973. Therefore it was necessary to carry on this study using molecular data. Our recent cladistic and molecular analyses as well as palaeontologic data led to a systematic and phylogenetic revision of the Euthecosomata: the Limacinoidea and of the Creseidae are not monophyletic, the other straight shells Euthecosomata are monophyletic (Corse et al. 2013). The Limacinoidea are invalidated; they are split into three families: Limacinidae Gray, 1847, Heliconoididae n. fam. and Thieleidae n. fam. The Creseidae Rampal, 1973 are validated but at least there are two genera Creseis Rang, 1828 and Boasia Dall, 1889; Styliola and Hyalocylis are considered incertae sedis. In the Cavoliniidae Gray, 1850 there are four subfamily: Cuvierininae Gray, 1850, Cliinae Jeffreys, 1869, Diacriinae n. subfam., Cavoliniinae Gray, 1850. The Creseidae Rampal, 1973 and the Cavoliniidae Gray, 1850 belong to the Cavolinioidea Gray, 1850. The species rank of most taxa is confirmed. New genera are proposed or reinstated: Telodiacria n. gen., Hyalaea de Blainville, 1821, Boasia Dall, 1889. The fossil Vaginella Daudin, 1800 is included within the Cuvierininae Gray, 1847. The spiral fossil Altaspiratella Korobkov, 1966 is no longer considered part of the Limacinidae Gray, 1847. Two phylogenetic hypotheses are analysed. According to molecular analyses in COI there is the double emergency of straight shell from two coiled shell lineages; in 28S there is monophyly; this last hypothesis we have kapt is the most parsimonious but requires some reserve and new investigations (Corse et al. 2013).