Gastropoda are soft-bodied mollusks with usually trochospiral (3D) dextral or sinistral shells, while Cephalopoda typically exhibit planispiral (2D) coiling; gastropods serve as important index fossils (e.g., Vicarya verneulli vicassa and Turricula flammea atjehensis) and form the basis of Oostingh’s Neogene biozonation in Java.
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