GASTROPODS BELONGING to the extinct family Cirridae Cossmann, 1916 are relatively rare elements of Mesozoic marine communities. The unusual change in shell coiling from dextral to sinistral during their ontogeny represents a character which makes their recognition in the fossil record easy. This shell feature is also known from members of the Paleozoic family Porcelliidae Koken inZittel, 1895, uniting the planispirally coiled Porcelliinae with the sinistrally coiled Agnesiinae Knight, 1956. This heterostrophy is not homologous with that of the Heterobranchia (Frýda and Blodgett, 2001). Shells of Porcelliinae and Agnesiinae bear an apertural slit, in contrast...

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