rostroconchians

Rostroconchians were an extinct class of marine mollusks that lived from the Cambrian period to the late Permian period. They are characterized by a single, conical shell that grew progressively longer and narrower. Unlike other mollusks, they lacked a distinct anterior and posterior end to their shell, and it appears they did not have a foot for locomotion in the way that gastropods do. Their shell shape suggests a burrowing lifestyle, where they likely anchored themselves in sediment. Fossil evidence indicates that some larger species may have had a coiled or twisted shell, though the basic conical form is the most common. Their internal anatomy is not well understood due to the scarcity of well-preserved specimens. Rostroconchians are considered a primitive group within the Mollusca, and their exact phylogenetic position has been debated by paleontologists. They are an important part of understanding early marine invertebrate evolution and the diversification of mollusks.