How diverse is the phylum Mollusca compared with insects and vertebrates?

The phylum Mollusca is recognized as one of the most diverse groups in the animal kingdom, alongside insects and vertebrates.1

In terms of described species, the diversity of these groups varies significantly:

• Mollusks: There are nearly 100,000 to 150,000 described species. This phylum encompasses a vast array of forms, ranging from shell-less Caudofoveata and chitons to gastropods (snails and slugs), bivalves (clams and oysters), and cephalopods (squids and octopuses).12
• Insects: As a class within the phylum Arthropoda, insects are significantly more numerous, with at least 1 million described species.3
• Vertebrates: This group comprises more than 76,000 living species.4

While mollusks exhibit immense ecological and structural variety, they represent a smaller number of described species compared to the vast diversity found within the class of insects.143