Rissoina (Rissoina) pusilla var. promyosoroides (Sacco, 1895) †
Turbo pusillus (Brocchi, 1814) † (basionym)
Rissoina pusilla (Brocchi, 1814) is an extinct species of small marine gastropod mollusc in the family Rissoinidae.[1] The species is known only from fossil material from Italy.[2]
The shell is minute, oblong, and blunt, with longitudinal folds. The whorls are weakly convex and closely spaced. The aperture is ovate, narrowing to a slightly pointed upper end. The shell length is approximately three lines (about 6–7mm).[2]
A fossil variety, Rissoina pusilla var. promyosoroides, has been described, characterized by a shorter, more pupoid shell and smaller initial whorls.[3]
Distribution
Known only from fossil deposits at San Giusto near Volterra, Italy.[2]
Additional fossil occurrences are reported from Piacenzian (Late Pliocene) deposits in Liguria, northwestern Italy, including Albenga, Rio Torsero near Ceriale, Bussana, and Bordighera, where the species was described as not rare.[3]
Taxonomy
The species was originally described by Giovanni Battista Brocchi in 1814 as Turbo pusillus based on fossil material from San Giusto near Volterra, Italy.[2] It was later transferred to the genus Rissoina, where it is currently placed.[1]
The name Rissoina pusilla var. promyosoroides, described by Federico Sacco in 1985, is treated as an unaccepted junior subjective synonym of Rissoina pusilla, representing intraspecific morphological variation rather than a distinct taxon.[1][3]
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