Belongs within: Heterobranchia. The Architectonicoidea are a group of marine gastropods uniting the Architectonicidae with related fossil families. The Architectonicidae, sundails, have discoidal or depressed-conical shells with a rather flat base, often with a very widely open umbilicus within which the coiled whorls are visible, and a sculpture of beaded spiral and radial ribs (Wilson… Continue reading Architectonicoidea