how are they classified ?
Opinions vary about the number of classes of molluscs. Some older works combine the Caudofoveata and Solenogasters into one class, the Aplacophora.
Mollusca
Opinions vary about the number of classes of molluscs; for example, the table below shows seven living classes, and two extinct ones. Although they are unlikely to form a clade, some older works combine the Caudofoveata and Solenogasters into one class, the Aplacophora. Two of the commonly recognized "classes" are known only from fossils.

Classification into higher taxa for these groups has been and remains problematic. A phylogenetic study suggests the Polyplacophora form a clade with a monophyletic Aplacophora. Additionally, it suggests a sister taxon relationship exists between the Bivalvia and the Gastropoda. Tentaculita may also be in Mollusca (see "Tentaculites").
what features of the squid are common to all members of the phylum mollusca UNANSWERABLE what are mollusca ? It is the second-largest phylum of invertebrate animals what are it different diversities ? Snails, Slugs, other gastropods clams to name a few how do they reproduce ? All produce eggs, from which may emerge trochophore larvae, more complex veliger larvae, or miniature adults.
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Mollusca [SEP] Classification
Opinions vary about the number of classes of molluscs; for example, the table below shows seven living classes, and two extinct ones. Although they are unlikely to form a clade, some older works combine the Caudofoveata and Solenogasters into one class, the Aplacophora. Two of the commonly recognized "classes" are known only from fossils. Classification into higher taxa for these groups has been and remains problematic. A phylogenetic study suggests the Polyplacophora form a clade with a monophyletic Aplacophora. Additionally, it suggests a sister taxon relationship exists between the Bivalvia and the Gastropoda. Tentaculita may also be in Mollusca (see "Tentaculites").