Racheliella, a new mathildoid gastropod genus (Gastropoda, lower Heterobranchia) from the Late Triassic St. Cassian Formation (N Italy)

摘要

The discovery of a preserved protoconch in the Late Triassic (Carnian) gastropod species Loxonema mersai from the Late Triassic St. Cassian Formation (N Italy) shows that this species has a larval shell displaying coaxial heterostrophy. This species does not represent the Palaeozoic genus Loxonema (with Silurian type species) but a new genus - Racheliella - belonging to the lower heterobranch superfamily Mathildoidea. The presence of this new genus adds to the high diversity and disparity of lower heterobranchs including Mathildoidea in the St. Cassian Formation and suggests that this group was much more diversified in the Late Triassic than in Recent seas. A lectotype is designated for Loxonema mersai.