Experts are divided on whether ______ should be classified as a mollusc or a 'probable bilaterian'.

______, an organism from about ______ million years ago, has sparked debate due to its ambiguous feeding structures.

Helcionellids appearance in fossil record

Helcionellids vs. Trilobites timeline

Helcionellids link to modern gastropods

As a result of this evolutionary change, more sophisticated ______ like gills were developed to aid the now enclosed organism.

Initially, the shells of the earliest ______ were likely made of a mineral called aragonite.

Fossils from the ______ period, such as Nectocaris and Plectronoceras, indicate that early cephalopods had shells.

The ______, specifically, exhibits intricate shell characteristics like septa and a siphuncle.

Despite having complex shells, early cephalopods like the Plectronoceras were not agile swimmers but ______ creatures.

Earliest bivalve fossils

Bivalves' ecological roles in modern aquatic environments

Scientists are reexamining the connections between living ______ classes and reclassifying certain ______ groups.

Molluscs, as part of the ______ superphylum, are genetically linked to ______ worms and various sea creatures.

The features of the earliest shared ______ of molluscs, like the presence of ______, are still uncertain.

Differing theories, such as the ______ and ______ models, have emerged from anatomical and genetic studies on molluscs.