Phyletic relationships and ecological implications between Pagodula vaginata (De Cristofori & Jan, 1832) and Pagodula echinata (Kiener, 1840) (Gastropoda, Muricidae)

Two closely related species, Pagodula vaginata (De Cristofori & Jan, 1832) and Pagodula echinata (Kiener, 1840), have been recently distinguished (Bauchet & Warén, 1985) on the grounds of larval shell morphology. The former has a multispiral protoconch, indicating a planktotrophic development, whilst the latter has a paucispiral protoconch, referable to a non-planktotrophic development. Both species occur in the Pleistocene deposits from Southern Italy. At that time, the two species lived in ecologically segregated populations, Pagodula vaginata being linked to deep-shelf and upper-slope bottoms, and Pagodula echinata to deeper bathyal bottoms. The extinction of Pagodula vaginata, in the upper part of the Lower Pleistocene or in the Middle Pleistocene, was probably caused by the Quaternary cooling. Pagodula echinata could then spread upward to about 100 m, attaining its present bathymetric range. The origin of Pagodula echinata is referred to Pagodula vaginata through a process involving the larval development, known as «loss of planktotrophy». Such a process probably occurred in the Mediterranean during the Middle- Upper Pliocene, within a general development of deep-sea benthos.