I presume it's an ermine because of the distinctive white pelage and size. I don't know the species of any of the molluscs. About half of the small specimens in "What is an Animal?" are arranged like this - no identifying tags, just a striking visual arrangement with as many unusual pairings as possible. The exhibit groups organisms by many lifestyle and structural strategies, and includes tags with IDs and information supporting the concepts being addressed, but it also involves many cases that are just decorative. Again, the museum's collections are semingly boundless and can support this - plenty of spare critters to use as decor, and it's nice to have them out of storage and on display in whatever capacity - but would it be so hard to provide a key next to these cases identifying the animals?