SYSTEMATICS AND PHYLOGENETICS OF LATE PALEOZOIC STREPTACIDAE (GASTROPODA)

The Family Streptacidae contains small, high-spired marine gastropods with heterostrophic protoconchs. They range in age from Devonian to Triassic, but the Devonian taxa are poorly preserved and of uncertain affinity. The genera Streptacis and Donaldina are known from the USA, Europe, China, and Australia. Reported North American Streptacidae include eleven species of Donaldina and five species of Streptacis which are well described, and possibly ten additional taxa for which critical details are lacking. The genus Platyconcha is known only from Europe, and Jiangxispira and Laxella are recently described genera from China.

Meek (1872) designated Streptacis whitfieldi as the genotype. J. Donald (1898) and J. Donald Longstaff (1917) placed European Streptacids in the genus Aclisina and designated Aclisina pulchra as the genotype. Knight (1931) followed this usage, but then Knight (1933) recognized that Miller (1889) previously had designated a different genotype for Aclisina. Knight (1933) created the new genus Donaldina with the European species D. grantonensis as genotype and reassigned taxa from Aclisina as used by Donald (1898), Longstaff (1917), and Knight (1931) to Donaldina.

Some authors have placed the Streptacidae in the superfamily Pyramidelloidea; others have placed the Streptacidae in their own superfamily and maintained that the oldest true member of the superfamily Pyramidelloidea is no older than Jurassic. The superfamily Pyramidelloidea is one of the most diverse families of molluscs, with over 6,000 Recent species. Phylogenetic analysis of the family Streptacidae Knight (1931) will resolve how they evolved, the degree of relationship with Recent Pyramidellidae, and whether the Pyramidelloidea originated in the Jurassic or in the late Paleozoic.