Final answer:
In the class Gastropoda, both slugs and nudibranchs lack a shell. They are unique within the class as most gastropods have a spiraled or coiled shell, but these two do not.
Step-by-step explanation:
In the class Gastropoda, nudibranchs, snails, slugs, and conches are all considered gastropods. However, among these options, it is slugs and nudibranchs that lack a shell. Gastropods can include shell-bearing species such as snails and conches, as well as species without shells like slugs and nudibranchs.
Gastropods exhibit a diverse range of habitats from land to freshwater bodies and marine environments. They may use their foot to crawl and have a well-developed head with eyes and tentacles. While most shelled gastropods possess a spiraled or coiled one-piece shell, slugs and nudibranchs do not have this characteristic, making them unique within the class.
So, the answer to the question, 'In class gastropoda, what lacks a shell?' would be A. Nudibranchs and C. Slugs.